IB Psychology: A Student's Guide (Second Edition) - Preview

IB PS YCHOLOG Y A

Student’s Guide

Travis Dixon

For my fellow teacher geeks who want to teach students cool stuff that one day they will use.

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Travis Dixon and Themantic Education™, 2024

All rights reserved. No part of this publication may be reproduced, scanned, stored or reprinted without the prior permission in writing from the author.

First published 2024

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ISBN: 978-0-9951390-1-5

IB PS YCHOLOG Y

A Student’s Guide

Travis Dixon

SECOND EDITION

PREFACE TO THE SECOND EDITION

Dear Student,

If you can google everything, why do you need this textbook? Why not choose any topic you like? Well, most students agree it’s more fun studying and discussing the same topics. Your teacher and I also know a lot about psychology. In this book, I have carefully selected topics and content that are the most interesting for students. We can save you the time of wading through the boring and irrelevant bits. By learning these facts first, hopefully you will be inspired to go and do more of your own research and learn more about psychology.

You’ll also be better off studying the content in this book because it’s the most effective way to learn, become an excellent psychologist, and do well on your exams.

Good luck,

Mr Dixon

Dear Teacher,

If the answer to any question can be googled or answered by AI, we don’t need to know anything. Students should be taught skills and critical thinking instead.

Unfortunately, this idea has pervaded teaching. Knowledge is undervalued. Courses and curriculums are designed around abstract ideas and concepts, with little regard for content or facts. This, I believe, is the fundamental problem facing schools, teachers and students.

The arguments against this sentiment are simple. Firstly, you can’t think critically about something you know nothing about. Therefore, all critical thinking begins with knowledge. This book is written with this simple truth in mind. All lessons are designed around three questions that get progressively more challenging, beginning with basic comprehension of content and moving into thinking critically about that content. Secondly, you can’t ask questions about something you know nothing about. Student-centred learning fails when students are given too much freedom too early. And the final reason is because knowledge is sticky. We learn new things by connecting it to things we already know. If we don’t know anything, we can’t learn anything.

This book is designed using our themantic model of curriculum design (thematic + semantic): using themes to improve semantic memory of content. It’s goal is to give you relevant and interesting content for students to love their introduction to psychology and do well on their exams.

I hope it helps,

Travis

CONTENTS

Introduction

Chapter 1: Criminology

Chapter 2: Cults

Chapter 3: Couples

Chapter 4: Memory

Chapter 5: Manipulation

Chapter 6: Depression

Chapter 7: Addiction

Chapter 8: Morality

Chapter 9: Personality

Chapter 10: Research Methods I

Chapter 11: The IA

Chapter 12: Technology (HL)

Chapter 13: Culture (HL)

Chapter 14: Motivation (HL)

Chapter 15: Research Methods II

Chapter 16: Exam Review

Glossary

References (HL)

Introduction

Welcome to the wonderful world of psychology – the scientific study of individual human behaviour and cognition. Psychologists observe people’s actions, look for patterns of behaviour and wonder why they happen. They also study cognition – the internal mental processes that happen inside our minds, like memory, thinking and decision-making.

The big question in psychology is “how and why do people think and act the way they do?” As you’ll learn in this course, there’s no easy answer to this question. It’s complicated. If you finish this textbook with more questions than answers, you’ve become an excellent psychologist.

Psychologists explain why things happen, but we can’t explain the why if we don’t know what it is we’re explaining. For example, our first lesson is about behaviour, so we’ll begin by finding out what a “behaviour” is. With this in mind, I like to use three levels of questions in Psychology. You’ll see these questions in every lesson. The first question usually begins with “What is…?” Then we get to the “How and why….” And then the final question challenges your critical thinking by making you think deeper about the subject.

You can become an excellent psychologist by mastering the basics first. The goal of this textbook, therefore, is to help you with the basic knowledge, develop a deep understanding of why things happen and then provide probing questions to challenge your critical thinking.

PREVIEW

Lessons

1. Behaviour

2. Cognition

3. Approaches

4. Psychological Research

5. Effects, Theories and Models

6. Course Overview

Critical Thinking Concepts: Bias, Causality, Change, Measurement, Perspective and Responsibility

This course has six general concepts that will develop your critical thinking.

• Measurement

• Causality

• Bias

• Change

• Responsibility

• Perspective

Each chapter will focus on one concept. For example, in “Criminology”, we’ll focus on “Causality.” Each lesson in this book ends with one specific key term related to the broader concept. These terms will be used to help develop your critical thinking and conceptual understanding. Challenge yourself to be able to answer these critical thinking questions at the end of each lesson.

1. Behaviour

What is behaviour?

Why do psychologists study behaviour?

Why is it difficult to study the prevalence of some behaviours?

Psychologists study behaviour – observable actions - things people do. Let’s look at two examples you’ll study in this course: conformity and compliance.

Conformity is when someone goes along with the group. They change their behaviour so they’re doing the same as everyone else. It can lead to terrible consequences like the Jonestown massacre.

Real World: Jonestown, 1978

In 1978, over 900 people committed mass-suicide in Jonestown, Guyana. These people were members of the Peoples Temple cult, led by Jim Jones. The cult started in 1954 in Indiana, USA. It had origins in positive Marxist and Christian ideals, like social equality. By the 1970s, Jones had a loyal following and moved his cult to Guyana, South America. He promised his followers a utopian society, but he became an authoritarian dictator. In the end, he tragically convinced all his followers to drink from a barrel of Kool-Aid which was laced with deadly cyanide.

PREVIEW

Jonestown is an extreme and tragic, real world example of conformity. Examples like this motivate psychologists to understand why people do the things they do. Another example that inspired a lot of research was the holocaust in World War II. This prompted psychologists to ask questions like, “how can ordinary people commit such horrible crimes?” While Nazism might have been a result of conformity, it was also a result of compliance –behaving in a particular way because someone has asked you to. Armies are based on rank and complying with orders from higher ranking officers. Some Nazi soldiers gave the reason, “we were just following orders.” This inspired social psychologists to design experiments to test the limits of compliance. You’ll learn more about the Stanley Milgram’s famous compliance experiments later in this course.

Once we know the causes of behaviours like compliance and conformity, we can use that knowledge in the real world. For instance, psychological theories of compliance can be used to influence behaviour in a positive way. Governments and businesses use compliance strategies to promote behaviour like recycling and conserving water.

In this lesson you’ve learned what we mean by the study of behaviour. In the next lesson we’ll look at cognition.

Psychologists study why people are compliant. Symbols of authority, like uniforms, are one reason.

Critical Thinking Concept: Change and prevalence

An example of a specific key term relevant to “change” is prevalence Psychologists study the prevalence of some behaviours, which means how common they are. For example, the prevalence of obesity is increasing in many countries. This means that more and more people are becoming obese (overweight). Psychologists research why this happens. They then publish their findings in studies like this Indonesian one in 2021 called “The correlation between sleep quality and the prevalence of obesity in school-age children.”

A related concept is prevalence rate – this is a percentage. It’s usually the percentage of people who have a particular health problem or disorder. For example, in 2013, a Chinese study reported a childhood obesity prevalence rate of 10.4%.

Some behaviours and problems are easier for psychologists to study than others. Why do you think this is? For example, do you think it’s as easy to measure the prevalence rate of conformity and compliance? Why?

PREVIEW

2. Cognition

What is cognition? Why do scientists study cognition? Why is it difficult to study cognition?

Psychology is the scientific study of how and why we think and act certain ways. Actions are behaviour, thinking is cognition – the internal mental processes.

It can be difficult to comprehend the term “cognition,” so here are some examples to help:

• Memory

• Decision making

• Perception

• Judgement

• Attention Cognition can be loosely defined as “thinking”. It’s what’s happening in our minds.

Can you see these things happening? No. I can’t see you remembering, or what you’re paying attention to or the decisions you’re making. This is why cognition is also called internal mental processes. They are the things happening within the mind. Think of it this way, if behaviour is the actions performed by the body, cognition is the mental processes performed by the mind. Let’s look at memory, decision making and attention to get a better understanding.

Memory is probably the most studied cognitive process. As a result, it’s been divided into many different types. For example, we have short-term memory and long-term memory. You can remember the words you’re reading right now in your short-term memory. If you think hard, you might remember something stored in your long-term memory like your first day of school. How much information you can keep in your short-term memory can affect your exam scores and academic success. Some people have amnesia and remember nothing while others have hyperthymia and remember everything. Psychologists have discovered this and dig deeper to find out why.

Similarly, the decisions we make shape our lives. Those decisions, however, can also be shaped by outside influences. This is one reason why psychologists study decision-making. One theory of decision-making is that we either think fast or slow when making a decision. If we think fast, we’re more likely to make a mistake. If we stop and think a bit longer, we’re more likely to make an accurate decision. This knowledge has been used in behavioural economics – the study of psychology in economics. For instance, the next time you’re shopping online, your decisions might be influenced by companies using behavioural economics to get you to buy their products.

Key Study: Gandhi and Anchoring Bias

Kahneman and Tversky designed an experiment to see how irrelevant information could affect people’s decision-making. They asked people to guess how old Indian leader Mahatma Gandhi was when he died. However, before people guessed they asked a question. One group was asked, “Was Gandhi older or younger than 9 years old when he died?”. The other group was asked, “Was Gandhi older or younger than 140 years old when he died?”. The lownumber group guessed he was 50 years old, while the high-number group guessed he was 67. This study demonstrates anchoring bias – the influence of an irrelevant number on judgement.

PREVIEW

Cognitive psychology seems to be growing in popularity alongside the increased use of technology in our lives. One cognitive process relevant here is attention – focusing on a particular thing. Like memory, it’s been divided into different parts, like selective and sustained attention. Selective attention means blocking some things out so you can concentrate on one thing, whereas sustained attention is the ability to focus on one thing for a long time. Both are important for some things. For example, when you write your Extended Essay for the IB Diploma, you want sustained attention. When you’re trying to read this textbook in a noisy classroom, you’ll need selective attention. Technology seems to be affecting our attention. Could the rise of ADHD be a result of technology? This is another thing cognitive psychologists study.

Just like with behaviour, if psychologists can understand and influence these cognitive processes, they can use them in applied fields of psychology, such as educational, clinical and health psychology, as well as in other areas like behavioural economics.

Exam Tip: Paper 1, Section A:

In this 4-mark question, you need to include an example to support your answer. Your example could be a real study, or a real-world example. This book includes one study and one realworld example for every topic so you can choose.

Critical Thinking Concept: Bias

A cognitive bias is a way of thinking that increases our chances of making mistakes. One example is the IKEA effect – the tendency for people to place a higher value on things they’ve assembled themselves (like kitset or flatpack furniture bought from IKEA). Another common bias is confirmation bias – people’s tendency to focus on and remember information that confirms their existing beliefs.

You can look online to find more examples. In fact, psychologists have identified over 100 specific cognitive biases. Why do you think these biases (or other cognitive processes) are difficult to study?

3. Approaches

PREVIEW

What are the different approaches in psychology?

Why do psychologists use different approaches?

What is the problem with dividing psychology into approaches?

Why do we do the things we do? Why do people commit crimes? Why do people fall in love, get married and then get divorced? Why do people go along with the group? It’s complicated. This is why psychologists take different approaches to study the same behaviours. For instance, a psychologist might take a biological approach by seeing how biological factors like genes and our brain affect behaviour. Another psychologist might take a sociocultural approach by looking at environmental factors, such as childhood and cultural influences. The cognitive approach looks at our thoughts and how they affect our actions. These are the three main approaches covered in the IB Psychology course. There are others, like the behaviourist approach (a.k.a. behaviourism) and the psychodynamic approach based on Sigmund Freud’s theories. Behaviourists believed that all behaviour was learned through conditioning whereas Freud believed our childhood experiences shaped our personality and affected our behaviour through subconscious forces.

What do we mean when we say a psychologist takes a particular approach? It’s usually referring to psychology professors at universities conducting research. They observe an interesting behaviour they want to study, ask questions why it happens and then narrow their focus to a particular range of explanations. Some might focus on biological factors, for instance, whereas others might focus on social or cultural ones.

Which approach do you think would be the most effective for studying criminal behaviour?

Let’s use two examples of famous psychologists to demonstrate. Adrian Raine is a British psychologist who studies criminology. He tries to find out why humans commit acts of violence. He wrote a popular book called An Anatomy of Violence: The Biological Roots of Crime. From the title, you can see what approach he prefers to explain crime – the biological approach. Raine looks at genes, hormones and the brain to explain violence.

Albert Bandura, on the other hand, focused on a different explanation for violence. Bandura became famous in the 1960s when he proposed his social learning theory of behaviour. This theory suggested that violent behaviours were learned by observing others and imitating them. His famous Bobo doll studies show that young children will act more violently after watching a violent adult. This seems like common sense now, but his theory contradicted the dominant theories of the time. By focusing on societal influences on behaviour, Bandura was taking a sociocultural approach.

Real World: Prison Populations

In the field of criminology, psychologists observe interesting patterns in the data and ask, “Why?” Take the following data from the UN Office of Drugs and Crime (UNODC):

• Approximately 90% of prisoners around the world are men.

• Most criminals commit their first crimes before the age of 25.

• Most criminals are young men.

• The rate of female criminals is increasing faster than that of male criminals.

PREVIEW

• The Americas have the highest number of prisoners, and Africa the lowest.

How would psychologists like Raine and Bandura take different approaches to investigate these patterns?

It’s useful to think of the distinct approaches when you’re first studying psychology. However, by the end of the course, you should see that the categories aren’t black-and-white. Many psychologists can’t be placed into a neat category. They prefer to focus on the behaviour and combine approaches to understand it. Bandura, for example, changed his theory in the 1980s to reflect our understanding of behaviour being a combination of biology and the environment. You’ll also see that none of these approaches can fully explain human behaviour, but they can all play a part.

Critical Thinking Concept: Perspective

The psychological approaches are sometimes called psychological perspectives. A perspective is a way of seeing something. In psychology, different psychologists have different perspectives. It’s easy for us to think of psychology in different perspectives (or approaches). However, this has problems. Think about the major topics we’ll study in this course like criminology, depression and memory. What is one problem with psychologists taking only one perspective or approach to study these behaviours? You could use the example of young men in prison.

4. Psychological Research

What is the scientific method?

Why do psychologists use the scientific method?

What is one limitation with using quantitative data in psychology?

Gathering data is essential in the scientific method.

PREVIEW

If one driving question in psychology is, “How and why do humans think and act the way they do?”, another is, “How do we know?” This brings us to the scientific study of behaviour and cognition. To be a science, psychology must use the scientific method. This means we don’t rely on faith, gut instinct or ancient wisdom, but we objectively gather data and draw conclusions from that data. This is why psychological studies are important – they are how we discover new knowledge.

The scientific method generally goes like this:

Make an observation >

Ask a question > Create a hypothesis > Test the hypothesis and gather data > Analyse the data > Draw conclusions > Publish result.

Here’s an example.

One day in 1964, two social psychologists called John Darley and Bibb Latane were reading a story about a woman who was murdered in New York City. They observed something strange about the story: there were 38 witnesses to the murder, but no one helped. They asked, why did no one help? They made a hypothesis that it was because there were other people around who also didn’t help. They predicted that if only one person saw the murder, that person would have been more likely to help. Darley and Latane designed an experiment to test their hypothesis They used a classroom in a university and had participants fill out a questionnaire. While that was happening, they slowly filled the room with smoke through an air vent. There were three different situations. A participant was either alone, with another participant, or with two actors pretending to be participants who were told to ignore the smoke. Researchers gathered data by timing how long it took the participant to leave the room and tell someone about the smoke. They analysed this data and found that when people were alone, they were much faster at getting help than when they were with someone else. They were slowest when there were two paid actors. Darley and Latane concluded that the more people there are around, the less likely they are to help. The smoky room study was published and became famous in psychology. It identified the bystander effect – the more people around in an emergency, the less likely they are to help.

Most psychological studies are quantitative. This means they are measuring things that can be represented as numbers. Averages can be calculated and results can be displayed on a graph. For example, to test how stressed out someone is, psychologists can give the “Perceived Stress Scale.” This is a questionnaire using Likert scales that gives a stress score out of 40. Or they might measure the levels of cortisol in their blood – this is the hormone released when you’re stressed. You’ll learn about a lot more methods of quantifying human thinking and behaviour throughout the course.

Likert scales are questions that ask participants to select a number along a range.

For example, “Are you enjoying psychology? 1 – Not at all, 2 – Not really 3 – Undecided, 4 – Somewhat, 5 – Very much.”

Critical Thinking Concept: Measurement

The key word in the scientific method is data. For us to get quantitative data, we need to measure something. The concept of measurement, therefore, is very important in psychological studies. For example, the severity of psychological disorders like depression, PTSD and eating disorders are measured using quantitative data. Patients answer questionnaires with Likert scale questions and each answer gets a score. The total scores are counted and the psychologist knows how severe someone’s disorder is. Can you see any limitations with trying to understand psychological disorders using only this quantitative data?

PREVIEW

5. Effects, Theories and Models

What are psychological theories and models?

How are theories and models connected to studies?

How can we evaluate theories and models?

A theory is a proposed explanation for why something happens. A psychological theory, therefore, is a proposed explanation for why people think or act the way they do. Let’s look at two famous theories from social psychology: social learning theory and realistic group conflict theory to demonstrate.

Social learning theory (SLT) was created in the 1960s by Albert Bandura. According to SLT, behaviour can be learned by observation. The reason we do the things we do, Bandura proposed, is because we’ve watched others do it and we copy them. For example, some kids might grow up to be more violent if they’ve observed and copied their violent parents or played a lot of violent video games. It seems like a simple explanation nowadays, but at the time it challenged other existing theories of behaviour.

SLT is a theory that can cover a wide range of behaviours. Other theories focus on specific behaviours. For example, realistic group conflict theory (RCT) tries to explain why people get into conflict with each other. According to this theory, groups of people get into conflict with each other when they are competing for limited resources. With these two examples, we can see how psychological theories work. They give a possible explanation for people’s behaviour.

Generally speaking, a theory explains why something happens, whereas a model summarises how it happens. A psychological model, therefore, shows how a psychological process or behaviour happens. A famous model is the multi-store model of memory. This is a summary of how memories are made. Another famous model is the dual processing model of decisionmaking. Dual means two, so this model shows how using two different types of thinking can lead to different decisions.

Psychological effects are patterns of behaviour that are very predictable because they have been observed in numerous studies. You already learned about the bystander effect. Other examples include the anchoring effect, the misinformation effect and the Google effect. One of the oldest and most famous examples is the Stroop Effect.

PREVIEW

Key Study: The Stroop Effect

John Ridley Stroop identified this effect almost 100 years ago in 1935. His famous experiment shows how we have automatic and controlled cognitive processes which interfere with each other. In the experiment’s congruent condition, the colour of the word and the name are the same (e.g. BLUE is written in blue ink). In the second, incongruent condition, the name and colour are different (e.g. BLUE is written in red ink). Participants are timed to see how fast they can read the ink colour. Consistently, people are slower in the incongruent condition. This is the Stroop Effect.

A good acronym to remember when evaluating an effect, theory or model is DEAL. First, describe the theory, then analyse the evidence, look at the applications and then consider other limitations

This is a sample from a Stroop test. Which one is easier?

Theories, models and effects are closely related to studies. If a study supports a theory or model, it will be more credible. This is one way we can evaluate the validity of theories and models – we can look at the supporting or contradictory evidence of their claims.

Similarly, a psychological model or theory is only as useful as its real-world applications. Therefore, the strength of any theory is how much it’s been used to help people in the real world. To evaluate a theory, we look at the value and extent of its applications. This brings us to our next lesson on the different fields of psychology.

Critical Thinking Concept: Causality

A psychological theory is only as good as its supporting evidence. In this course, you’ll learn how to evaluate the validity of psychological evidence. One way is to consider causality – when one variable is directly responsible for the change in another. Experiments test causality. For example, Bandura’s famous experiment showed observing aggressive models caused an increase in aggression in children. Throughout this course, you will learn to evaluate theories and psychological studies like Bandura’s. Can you see any problems with using Bandura’s study on American three-year-olds in the 1960s to conclude that aggression is caused by watching other violent people?

PREVIEW

6. IB Psychology Course Overview

The IB Psychology course is designed around the 3Cs: Content, Contexts and Concepts. This is confusing at first, but this textbook covers the 3Cs logically and systematically. How the course content fits with exam questions is covered in more detail in the “Exam Preparation” chapter. By the time you’re ready for exams, it won’t feel so overwhelming.

The Contexts

There are four contexts. Your understanding of these contexts is assessed in Paper One.

• Learning and cognition

• Human relationships

• Health and wellness

• Human development

The Content

In IB Psychology, content knowledge is divided into two parts:

• Approaches: biological, cognitive and sociocultural.

• Research methodology: methods, sampling, data analysis and interpretation. The approaches are mixed into the four contexts. For example, in “Addiction,” you’ll learn about biological, cognitive and sociocultural explanations for why people abuse drugs like opioids. In criminology, you’ll focus on the biological approach for interpersonal aggression. Research methods are also mixed into the contexts. Each context has one practical investigation. In this investigation, you’ll learn about the research method, data analysis and interpretation. You will also learn more about research methods when you’re completing the Internal Assessment (IA).

Chapters in the IB Contexts

Human Relationships Learning and Cognition

Group Behaviour Cults

Interpersonal RelationshipsAggression Criminology

Social Relationships Couples*

*Practical Survey / Questionnaire

Thinking and Learning Manipulation

Cognitive Processes Memory*

*Practical Experiment

Health and Wellness Human Development

Health Problems Addiction Development of Self Personality

Mental Health Depression* Models of Development Morality

*Practical Interview

This table shows how the chapters of this textbook map onto the different contexts and topics in the IB Psychology course.

The Concepts

*Practical Observation

PREVIEW

There are six concepts in the IB Psychology course. To simplify things, this textbook focuses on one concept per chapter. Next to each concept, I have a suggested learning. These outcomes are not stated in the IB Psychology Guide. I have created them to make it easier for you to study. They apply to psychological research and practice.

• Bias: Evaluate methods used to reduce bias.

• Causality: Evaluate methods used to understand causality.

• Change: Evaluate methods used to change human behaviour.

• Measurement: Evaluate methods used to accurately measure behaviour.

• Perspective: Evaluate different perspectives for understanding behaviour.

• Responsibility: Evaluate methods used to conduct responsible research and practice.

You’re probably feeling overwhelmed. That’s OK. There is a lot to learn in IB Psychology. Imagine we’re building a tower of psychological knowledge in your brain. Right now, we’re standing on an empty building site. We’re only going to build this tower one block at a time. Every new word you learn in this course is a building block. By adding these blocks into your brain, you’ll find them easier to connect to other blocks you’ve already got.

You’re not going to build anything if you stand and stare at the blocks. You won’t learn anything if you don’t pick up a pen and this textbook and start working. Use your highlighter, take notes in the margin, keep a workbook for your notes. The more you do, the more you’ll think and the more you’ll learn. It’s that simple.

IB Psychology: A Student’s Guide (Second Edition) PRE-ORDERS ONLY

Chapter 1: Criminology

Are violent criminals born or made? The nature versus nurture debate has raged in criminology for 150 years. In this chapter, we’ll focus on the “nature” side of the debate. You’ll learn about the major biological factors that cause criminal behaviour. These include:

• Brain abnormalities

• Genetics

• Chemical messengers

We’ll focus on explanations for two types of aggression. The first is impulsive aggression – when someone reacts violently without thinking. The second type is premeditated aggression – when someone carefully plans out their violent acts. Most of the explanations in this chapter are for impulsive aggression.

The focus concept in this chapter is causality. In psychology, causality is when one factor is responsible for a direct change in another. Once you understand the key terms and biological explanations of behaviour, see if you can use causality to critically evaluate what you’ve learned.

LESSONS

1. The Criminal Brain

1.1 Localisation of Function

1.2 Neuroplasticity

1.3 Brain Imaging

2. Chemical Messengers

2.1 Hormones: Testosterone

2.2 Testosterone and the Brain

2.3 Neurotransmitters: Serotonin

2.4 Serotonin and the Brain

3. Genetics

3.1 The Warrior Gene

3.2 Animal Models: MAOA Knockouts

4. Research

4.1 Biological Reductionism

4.2 Ethics in Animal Research

1. The Criminal Brain

1.1 Localisation of Function

What are the functions of the amygdala and the prefrontal cortex (PFC)?

Why do abnormalities in the PFC and amygdala increase aggression?

Why is causality difficult to prove in criminal brain studies?

The brain affects behaviour. More specifically, different parts of the brain will influence different behaviours. This is because of localisation of function – the fact that different functions of the brain are localised in specific areas. For crime and aggression, the prefrontal cortex (PFC) and the amygdala are two important regions.

The Prefrontal Cortex

PREVIEW

The PFC is located at the very front of our brain. Its primary functions are related to thinking and decision-making. For example, it allows us to predict the consequences of our actions. It also helps inhibit impulsive behaviour. It’s like the brain’s brakes – it stops us doing stupid stuff.

The link between the PFC and behaviour was first shown in the famous case of Phineas Gage, an American railroad worker. In 1848, Gage suffered an accident while exploding rocks with dynamite. The three-foot iron bar he was using sparked the dynamite powder and the bar shot out of his hands, up under his left eye, through his skull and out his head. Remarkably, Gage survived and didn’t even lose consciousness. He was a medical marvel, but it’s what happened after that’s relevant for psychology. After the accident, Gage’s personality and behaviour changed. He had a hard time controlling himself and he was fired from his job. The doctor who treated Gage noticed that after the accident his “… mind was radically changed, so decidedly that his friends and acquaintances said he was ‘no longer Gage.’” This was the first observation of how brain damage can change behaviour. Since then, we’ve learned how violent criminals also have abnormalities in their PFCs that affect their behaviour.

Phineas Gage with the iron bar that shot through his prefrontal cortex.

The Amygdala

While the PFC is the thinking centre, the amygdala is the emotional centre. It is the centre of emotions like empathy, fear and anger. It also detects threats in our environment and activates our fight-or-flight response. A hyper-responsive amygdala is easily activated. This can cause impulsive aggression or increased anger. If someone has a hypo-responsive amygdala (less activity), on the other hand, they might lack empathy or fear.

Real World: Charles Whitman

Brain abnormalities and their link to violent behaviour can be seen in the case of Charles Whitman. In 1966, Whitman climbed to the top of the observation tower overlooking the University of Texas in Austin. He had a large case packed with guns, ammunition and supplies to last for days. For no apparent reason, Whitman started shooting innocent people on the ground below. He killed 14 people and injured 30 others. Before the shooting, Whitman also killed his wife and his mother. In his suicide note, Whitman stated, “I cannot rationally pinpoint any specific reason for doing this.” He asked for an autopsy to be conducted on his brain because he was suffering from “overwhelming violent impulses.” After Whitman was shot and killed, an autopsy was performed. They found a tumour impacting his amygdala. Coincidence? You can read more about Whitman on our blog: “Mass shootings in the US: The Case of Charles Whitman.”

PREVIEW

The PFC, amygdala and the hippocampus are the three parts of the brain you’ll learn most about in this course.

We have two amygdala on each side of our brains and the plural for amygdala is amygdalae.

Abnormalities in the PFC and amygdala affect aggression. Different damage causes different types of aggression like premeditated or impulsive aggression. Serial killers, for example, tend to have fully functioning and developed PFCs. They can think and plan their actions so they don’t get caught. Their amygdalae,

however, might be smaller and hypo-functioning, which is why they have no fear and lack empathy for their victims. An impulsive murderer who kills someone in a fit of rage, on the other hand, may have a smaller or underdeveloped PFC and a hyper-responsive amygdala. They’re quick to anger and lack the ability to inhibit their impulsive, aggressive reaction.

Critical Thinking Concept: Causality and Alternative Explanations

Causality is when one thing leads to a direct change in another. We can conclude causality when there are no alternative explanations. In this course, try to think critically by looking for alternative explanations. Take Phineas Gage, for example. What is one alternative explanation for why his behaviour changed after the accident? Similarly, you have just learned there are links between brain abnormalities and violence. Why do you think causality is difficult to prove in modern criminal brain studies?

1.2 Neuroplasticity

What is neuroplasticity?

How and why do abuse and neglect change the PFC and amygdala?

Why are natural experiments useful when studying neuroplasticity?

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After 150 years of research, we know that abnormalities in the amygdala and the prefrontal cortex are strongly linked with aggression and crime. But what causes these abnormalities? Criminologists originally believed it was simply genetics – criminals are born with bad brains. However, we now know it’s more complicated. The environment can shape brain development. This is known as neuroplasticity – the brain’s ability to change because of experience. Two powerful environmental factors that cause neuroplastic changes are childhood abuse and neglect.

Neglect and the PFC

Childhood neglect leads to underdeveloped PFCs because a developing brain needs lots of stimulation. We’re born with around 85 billion brain cells (called neurons). At first, they’re a cluttered, disconnected mess. However, if we have lots of stimulation, the neurons make connections with each other and brain regions develop. If a child is severely neglected, they lack the stimulation needed for their brain to develop properly. This results in reduced volume in the PFC and other areas.

Abuse and the Amygdala

Extreme childhood abuse causes the amygdala to be hyper-responsive. This neuroplastic change is a survival adaptation. The amygdala keeps us safe by detecting threats and activating our fightor-flight response. A kid in a violent household has a better chance of survival if their amygdala is hyper-responsive. They become hypervigilant – ready to react to any sign of danger. One of the most consistent findings in studies on brain development is that abusive parenting is correlated with amygdala hyper-responsivity.

Our brains develop by individual brain cells, called neurons, connecting with other neurons. Abuse and neglect cause damage to the brain because they affect these connections.

Key Study : Childhood Abuse and the Amygdala (McCrory et al.)

The aim of this study was to see how abuse influences amygdala activity. Two groups of London teenagers were recruited. The first group had been abused from a young age. The second group was a control group, similar in age, socioeconomic status and ethnicity. The children had their brain activity scanned using a brain scanner called an fMRI. While in the machine, pictures of angry or happy faces flashed on the screen. As predicted, the maltreated group had higher amygdala activity when shown the angry faces. This shows how the abuse has prepared their brain to respond faster to threats in their environment. The researchers concluded that the brain adapts to childhood abuse.

Abuse and neglect also shrink the PFC and amygdala because of stress hormones like cortisol. Cortisol is a stress hormone like adrenaline. In short bursts, it’s helpful. However, chronic release of cortisol from the stress of abuse and neglect can damage neurons and result in atrophy (shrinking) of the brain.

Fun Fact: The amygdala detects threats before we are consciously aware of danger. In McCrory’s study, the faces were only shown for 16 milliseconds. Even though their amygdalae were activated, the participants wouldn’t have known what they saw.

Critical Thinking Concept: Causality in Natural Experiments

McCrory’s study on London kids is an example of a natural experiment - when the independent variable in an experiment is naturally occurring. This means participants can’t be randomly allocated to conditions and the IV is beyond the control of the researchers. In this study, the independent variable is childhood abuse. This happened naturally in the kids’ homes. The study also used a matched-pairs design. This is when each person in the experimental group is matched with someone else who is similar in many ways, like age, gender and socioeconomic status. This helps control for these extraneous variables. Why do you think natural experiments are useful in studying the possible causal relationship between childhood maltreatment (abuse and neglect) and brain development? Can you see any limitations with making causal conclusions from natural experiments?

1.3 Brain Imaging

What do MRIs and fMRIs measure?

Why was the invention of brain imaging technology valuable in psychology?

What is one limitation of brain imaging studies?

Brain imaging is a valuable tool in neuropsychological studies. The most common are MRI and fMRI. These technologies are valuable in many fields, including neuroplasticity.

The magnetic resonance Imaging (MRI) machine was first invented in the 1970s. TheiMRI measures brain structure – the size and shape of the brain. It’s like getting an X-ray of the brain, but instead of bones, it shows brain matter. MRI is used to identify tumors and other brain damage. If Charles Whitman were alive today, he wouldn’t have needed to have an autopsy to study his brain. His tumor could have been identified using MRI machines, perhaps saving himself and his innocent victims.

Functional MRI (fMRI) was developed from MRI in the 1990s. It measures the level and location of brain activity in specific brain regions. Psychologists place people in fMRI machines, get them to perform a task and measure their brain activity.

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Both MRI and fMRI technologies have been invaluable in neuroplasticity experiments. Beforehand, psychologists relied on animal experiments, which required euthanizing and dissecting animal brains to see neuroplastic changes. Now, they can scan human brains before and after an experiment to see neuroplasticity in action without harming animals.

Brain imaging is especially valuable in neurocriminology – the use of neuroscience and brain imaging to understand criminal behaviour. Neurocriminologists can use MRI to design natural experiments that study the relationship between the brain and criminal behaviour.

Key Study: MRI Imaging of the Criminal Brain (Saious-Turner et al.)

Psychologists gathered data from over 800 male criminals. They used MRI brain scans and psychological tests to find three specific groups: homicide (i.e. murderers), violent non-homicide (e.g. assault) and non-violent criminals (e.g. drunk drivers). They controlled for age, IQ, drug use, psychotic disorders and time in prison. The results showed distinct differences in the brains of the murderers compared to the other two groups. The homicide group had reduced grey matter in parts of their PFCs, including the ventromedial PFC (vmPFC) and the dorsolateral PFC (dlPFC). These regions help us understand other people’s emotions, as well as how we control our own emotions and behaviour. The study was the first to show how brain abnormalities in murderers are distinct from other violent and non-violent criminals.

An MRI scan image. MRIs show the size and structure of the brain.

fMRI shows levels of activity in the brain. It can tell what parts are activated during particular tasks.

Studies on the brains of criminals show the value of MRIs in designing natural experiments. Without fMRIs and MRIs, it’s impossible to see the structural and functional differences in criminal brains without waiting for them to die and conducting post-mortem dissections. This is why the invention of brain imaging technologies like MRI and fMRI have increased the quantity and quality of neuropsychological research.

Critical Thinking Concept: Causality and Brain Imaging

fMRIs are limited in what they can measure. Participants must lay completely still. Any movement affects the results. If we want to understand aggression and violence, why is this a big limitation?

MRI studies, like the criminal brain study, are also limited. The participants are gathered after they have committed a crime. The researchers themselves admitted this prevents them from proving causality. Why?

2. Chemical Messengers

2.1 Hormones: Testosterone

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What is a chemical messenger? What is testosterone?

Why does testosterone affect aggression?

Why do psychologists use correlational studies?

Chemical messengers are chemicals that flow through our blood and brain sending messages. The messages they send affect our behaviour. Two examples are hormones and neurotransmitters

Hormones are chemicals that travel through our bloodstream. They send messages throughout the body, affecting our biology and changing our behaviour. The system of glands that release hormones is called the endocrine system. Testosterone is the male sex hormone linked with aggression, status seeking and libido (sex drive). Testosterone is produced in the testes of males and in the ovaries of females. Psychologists have long hypothesized that men are more aggressive than women because of testosterone. Evidence for this comes from animal studies.

You can read about a rat study on testosterone on our blog:“Key Study: Testosterone and aggression in rats (Albert et al. 1986).”

The first study to show testosterone affects aggression was in 1849. Arnold Berthold castrated young roosters and observed changes in their physical appearance and behaviour. He also transplanted and reinserted testicles to see what would happen. He found that castration reduced aggression. When testicles were reinserted, the aggressive behaviour returned. This suggests that testosterone, which is produced in the testes, causes this aggression. More recent animal studies show consistent findings. Researchers follow the same procedure of changing testosterone levels through castration and then artificially injecting testosterone to see what happens. They also find that castration reduces aggression and injecting

testosterone increases it. This shows the link between testosterone levels and aggression.

But what about humans? It’s difficult to find male volunteers for castration studies. However, researchers can conduct correlational studies. They find a group of males, measure their testosterone and aggression levels and see if they’re correlated. For example, psychologists measure aggression and testosterone in prisoners. One study found that prisoners who committed the most violent acts had the highest testosterone. Similar results have been found in studies of sexual violence including one that investigated several groups of sex offenders, including rapists and child molesters, and the most violent offenders had higher testosterone levels than those who committed less violent crimes. This is one reason why chemical castration of sex offenders is used to reduce violent sexual crimes in several countries.

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Real World: Castrating Convicts

Castration is a punishment used around the world for violent sex offenders, particularly pedophiles and child molesters. This could be surgical castration, where the testicles are surgically removed. More commonly, however, it’s chemical castration – using drugs or chemicals to stop the production of testosterone. Cyproterone acetate is the common drug used in chemical castration. It reduces sex crimes by eliminating testosterone and reducing aggression and libido. Cyproterone has also been used in the treatment of other aggressive behaviours. For example, it was given to one 82-year-old male patient with dementia to control his aggression.

This might explain why most violent criminals are young men – testosterone levels are highest in males 15 to 29 years old. In the next lesson, we’ll find out why testosterone influences aggression.

Critical Thinking Concept: Correlation vs Causation

In psychological studies, causation means that one factor causes a direct change in another. For example, increases in testosterone levels will cause an increase in aggression. Correlation, on the other hand, means that as one thing changes, so does the other. For example, as testosterone increases, so does aggression. However, we don’t know which one is causing the change in the other. For example, studies on violent prisoners show that they have higher testosterone levels than less violent prisoners. This could mean that the testosterone is causing the violence, or perhaps their history of violence has resulted in higher testosterone levels.

If understanding causality is the goal in psychology, why do you think psychologists use correlational studies?

Different glands throughout the body release different hormones. As levels of hormones change, they can affect our behaviour.

2.2 Testosterone and the Brain

What is social threat?

Why does testosterone affect aggression?

How does a randomised controlled trial (RCT) demonstrate causality?

Human studies have shown a correlation between testosterone and aggression. However, these findings are inconsistent and sometimes the correlations are weak. Psychologists argue it’s because they measure baseline testosterone. They don’t account for constantly changing hormone levels. For example, your testosterone levels can change based on your sleep, diet, exercise and when you’ve just won or lost a competition. Understanding how sudden fluctuations in testosterone affects aggression is more helpful than baseline measures.

One possible reason testosterone increases aggression is because it increases the reactivity of the amygdala. As well as sparking negative emotions, the amygdala also detects threats in our environment. Once a threat is detected, our stress response is triggered and stress hormones are released. Depending on the threat, the amygdala might also spark emotions like fear and anger. An important type of threat is social threat – this is when someone poses a challenge to us that’s scary or dangerous. A social threat might also challenge our social status. The amygdala helps detect social threats. Therefore, if someone has increased activity in their amygdala due to high testosterone, they might get angrier and aggressive faster to threats than other people.

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How do we know? Researchers give participants either testosterone or a placebo, place them in an fMRI brain scanner and expose them to pictures of happy, angry and neutral faces. They measure their brain activity and compare the data. The results of these studies show that testosterone increases amygdala reactivity to angry faces. Researchers assume the testosterone is helping the amygdala detect threats in our environment. The following study shows that motivation to approach or avoid the threat also matters.

People with anger and aggression problems, like those with antisocial personality disorder (ASPD), tend to have more reactive amygdalae. Men are three times as likely as women to have ASPD, which could be the result of testosterone.

Key Study: Testosterone and the Amygdala (Radke et al.)

The aim of this fMRI study was to see if testosterone affects amygdala reactivity to angry faces when someone is motivated to approach or avoid an angry face. The researchers used a double-blind, placebo-controlled randomised experiment. They gave a sample of healthy women some testosterone or a placebo and then put them in the fMRI. While in the fMRI, they were shown angry or happy faces and asked to either approach or avoid the face by pushing a joystick to make the face larger (approach) or pull the joystick to make the face smaller (avoid). The results showed that those in the testosterone group had the highest amygdala activation when approaching the angry faces. These results show how testosterone pushes us towards dealing with threats in our environment by increasing amygdala activity. This increases the chances of an aggressive reaction to a threat.

Radke et al.’s study shows that testosterone affects the amygdala when dealing with a social threat. Aggression is one way to deal with threats, as well as to obtain and maintain high social status. Testosterone might also drive behaviours that deal with social threats in other ways. For example, other studies have found testosterone can increase generosity and cooperation. Therefore, it might not be as simple as higher testosterone causes aggression. Instead, higher testosterone may drive status-seeking behaviour, with individuals behaving differently depending on the best way to increase status.

Interestingly, testosterone replacement therapy (TRT) has been used to help people with depression and anxiety. Maybe it works because it helps people confront their fears, rather than avoid them.

A social threat is when someone poses a potential challenge that’s scary, dangerous or challenging to our social status. Testosterone helps us deal with these threats.

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Critical Thinking Concept: Causality and Randomised, Controlled Trials

Radke et al.’s study was a randomised, placebo-controlled, double-blind true experiment. This is the “gold-standard” in psychological research when trying to establish causality. It’s sometimes more simply called a randomised controlled trial (or RCT). An RCT prevents extraneous variables affecting the results. Randomised means participants were randomly selected to go into the testosterone or placebo group. Placebo-controlled means one group was given a placebo to compare with the experimental group (who got testosterone). Double-blind means both the participants and the researcher collecting the data did not know which group each participant was in. How does a randomised controlled trial (RCT) show causality? Tip: Plan your answer using flow charts and diagrams first.

2.3 Neurotransmitters: Serotonin

What is neurotransmission?

Why does neurotransmission affect behaviour?

All behaviour starts with brain cells called neurons. These neurons communicate with each other through a process called neurotransmission. At the heart of the neurotransmission process are other chemical messengers called neurotransmitters

How can researchers establish causality by controlling for the placebo effect? Our brain is made up of billions of neurons (about 86 billion, to be precise). Everything we do is based on how these neurons communicate with each other through neurotransmission.

The process of neurotransmission is as follows:

1. Neurotransmitters are built in the neuron’s cell body then grouped together into sacs called vesicles.

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2. The vesicles travel down the axon to the axon terminals where the neurotransmitters are released into the synaptic cleft – the space between two neurons.

3. Neurotransmitters bind to receptor sites on the postsynaptic neuron. Each neurotransmitter has specific receptor sites it can bind to. It’s like a “lock and key” and only the right key (the neurotransmitter) will unlock the right lock (the receptor site).

4. After a neurotransmitter binds to the receptor, it’s released back into the synaptic cleft. Here, it’s digested by enzymes and flushed out of the system or reabsorbed into the presynaptic neuron to be recycled and reused (this is called reuptake).

Neurotransmitters

There are over 100 different neurotransmitters. Each have specific functions and affect different behaviours. Three commonly studied neurotransmitters are serotonin, dopamine and glutamate. Serotonin affects mood, dopamine affects pleasure and motivation, and glutamate affects memory. Changes in these neurotransmitters will change your behaviour. This is why drugs affect your behaviour – they are influencing neurotransmission.

Real World: Blackout Drunk

Alcohol increases dopamine and serotonin. This is why people feel good after a couple of drinks. However, when someone drinks too much, they have a blackout –their brain can’t form new memories, and they wake up not remembering what they’ve done (or so I’ve been told). This is because alcohol binds to glutamate receptors and prevents them from working properly. This reduces glutamate binding and glutamate can’t perform its memory-making functions. With lots of alcohol, the glutamate is inhibited and no new memories are made. This results in a blackout.

Understanding the process of neurotransmission has many applications. If neurotransmitters affect behaviour, then psychologists can change behaviour by altering different steps in the process. Examples of this are explained in the chapter on depression.

Critical Thinking Concept: Causality and the Placebo Effect

Psychologists know drugs affect behaviour from animal experiments. For example, they can give a rat alcohol and test their maze-learning abilities. However, it’s more difficult with humans because of the placebo effect. This is when something has an effect simply because someone believes it will have an effect. For example, people might get tipsy if they think they’re drinking alcohol, even if it’s 0% beer. Pills can cure illness even if they’re made from sugar. They work because of the amazing power of the mind to change the body. Imagine you wanted to test a new drug that you think will improve memory. How would you stop the placebo effect from ruining your results? Tip: Consider an RCT.

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2.4 Serotonin and the Brain

What is the serotonin deficit hypothesis of aggression?

Why does serotonin affect aggression? What moderating variables might affect serotonin’s causality?

Serotonin is a neurotransmitter that influences our mood. Most people know about serotonin because of its connection with depression. In the 1960s, psychologists proposed the monoamine hypothesis of depression because they thought monoamine neurotransmitters (like dopamine and serotonin) were the cause of depression. So many studies linked serotonin to depression that the hypothesis became known as the serotonin hypothesis of depression.

However, psychologists have also proposed a serotonin deficit hypothesis of aggression. This theory posits that low levels of serotonin cause aggression. This hypothesis is supported by a range of studies on children, animals and violent criminals. For example, criminals and teenagers with a history of antisocial behaviour tend to have less serotonin than other people. In animals, psychologists have created genetically modified rats with low serotonin and find they’re more aggressive. Similarly, researchers have found that injecting serotonin into the amygdala of rats reduces their aggression. The supporting evidence for the serotonin deficiency hypothesis is such that “…one widely cited author called the inverse relationship between serotonin activity and aggression ‘perhaps the most reliable finding in the history of psychiatry’”.

We’ve established that serotonin influences aggression. We can now explore more deeply the reasons why. Let’s look at two factors: cognition and the brain.

Serotonin could affect aggression because of its impact on thinking and brain activity.

Serotonin and the PFC

Cognitive Explanation: Inhibitory Response Control

There are two major categories of aggression: reactive and premeditated. Premeditated aggression means that the person has planned out their actions. For example, serial killers premeditate their murders. They plan carefully so they don’t get caught. Low serotonin might not explain this kind of aggression. Serotonin is more closely linked to impulsive, reactive aggression. This is when someone flies off the handle in a rage and reacts aggressively without thinking. This could be because they lack inhibitory response control – the ability to think carefully about their responses and to inhibit any that may have negative consequences. Serotonin influences inhibitory response control. Someone with low levels of serotonin, therefore, might not be able to stop themselves from reacting violently when provoked.

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Serotonin might affect thinking because it affects the brain. Inhibitory response control happens in the prefrontal cortex (PFC). The PFC is the brakes on our behaviour. It allows us to stop and think through the consequences of our actions. Low serotonin can reduce activity in the PFC. This means someone with low serotonin might not have the brain power to perform inhibitory response control and they will react with impulsive aggression. Low serotonin can also disrupt the neural pathways between the amygdala and the PFC. The amygdala is where anger and aggression can come from. It’s the fire. The PFC can put out this fire by top-down processing –for example, by thinking about the consequences of an aggressive reaction. But if low serotonin disrupts that connection, the fire in the amygdala might rage while the PFC can’t put it out.

Key Study: Serotonin and the PFC (Passamonti et al.)

The aim of this fMRI study was to see how serotonin levels affect brain activity when viewing angry faces. To reduce serotonin levels, the researchers used “acute tryptophan depletion.” Tryptophan is an amino acid that helps build serotonin, so without it, serotonin levels drop. Participants consumed either a placebo drink or one that reduces tryptophan (and thus serotonin). The results showed that when viewing angry faces in the fMRI, participants with lower serotonin had reduced function in their PFC. The results also showed a disruption in communication between the amygdala and the PFC when viewing angry faces. The researchers concluded that serotonin influences the PFC and PFC-amygdala connectivity, which is why low serotonin might influence aggression.

Serotonin changes behaviour. But what changes serotonin? Genes play a role, and so does diet. That’s because monoamine neurotransmitters like serotonin are built from amino acids like tryptophan, which can be found in food. Omega-3 fatty acids also help serotonin production. This means we can naturally boost our serotonin levels by eating healthy foods rich in omega-3 fatty acids and tryptophan. In fact, the link between serotonin, diet and aggression is well-established. This has prompted prisons to experiment with giving inmates better food and nutritional supplements, including omega-3s. In one UK prison, researchers found giving inmates nutritional supplements reduced violent offenses in the prison by 30%. Similarly, a Norwegian prison used multivitamins and had a 34% reduction in misconduct offenses. In Singapore, one randomized controlled experiment was conducted with omega-3 supplements. They found reductions in aggression, especially impulsive, reactive aggression. These reductions in aggression could be because the diets increased serotonin production. These studies show the importance of studying origins of behaviour. If we know how diet affects the brain and how the brain affects behaviour, we can create effective intervention strategies based on diet to reduce antisocial behaviour and promote prosocial behaviour.

If serotonin is made from healthy food, then improving the diets of prisoners could increase serotonin and reduce violence.

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Critical Thinking Concept: Causality and Moderating Variables

The relationship between serotonin and aggression is more complex than simply saying if you increase someone’s serotonin, then they will become less aggressive and vice-versa. There are numerous moderating variables that make this relationship complex. A moderating variable is a third variable that influences the relationship between two factors, like serotonin and aggression. For example, activity in the prefrontal cortex is one moderating variable in the serotonin-aggression relationship. Everyone has different PFCs, so it makes it more complicated than simply A > B.

Can you think of any other factors that might influence the serotoninaggression relationship? What other factors might affect someone’s serotonin in the first place?

3. Genetics

3.1 The Warrior Gene

What is the warrior gene (MAOA)?

Why does the MAOA-L variant affect aggression?

Why are natural experiments useful when studying aggression?

You’ve learned how hormones, neurotransmitters and brain activity all contribute to criminal behaviour. Let’s now look at genetics.

Twin Studies

Concordance rates in twin studies are how psychologists study the extent behaviours are genetically inherited. A concordance rate is the frequency that two twins concur (or match up) with each other on a specific behaviour. The concordance rates of identical twins (monozygotic – MZ) are compared with non-identical twins (fraternal or dizygotic twins – DZ). MZ twins have 100% of their genes in common, while DZ twins share about 50%. If a behaviour is 100% genetic, then the concordance rate should be 100% in MZ twins.

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The first ever criminology twin study was way back in 1929 by Joannes Lange. He found 30 pairs of twins in different prisons – 13 MZ and 17 DZ . In the MZ group, 10 of the 13 pairs of twins were both in prison. This means the concordance rate for criminal behaviour was 77% (10/13). In the DZ group, the concordance rate was only 12% (2/17). This suggests a strong influence of genes on crime. Several following studies used similar methods, and the average concordance rates of these studies was 75% for MZ twins and 25% for DZ twins.

The Warrior Gene

Early criminology studies used concordance rates of MZ and DZ twins to see if criminality was nature or nurture.

Twin studies and concordance rates show genes influence behaviour. With advances in genome technology, we can now identify specific genes. Let’s look at one so closely linked to aggression it’s nicknamed “the warrior gene.” Its scientific name is the monoamine oxidase A gene (or the MAOA gene for short).

There are two types of MAOA gene: the MAOA-L (low) or MAOA-H (high). It is the MAOA-L variant that is linked with crime and violence. The link between MAOA and violence was discovered by Han Brunner in the 1990s. In one Dutch family, several of the men suffered from low IQ and “…a tendency toward aggressive outbursts, often in response to anger, fear, or frustration.” Brunner found they all had the MAOA-L gene. Since then, numerous studies have implicated the MAOA-L gene in aggression.

MAOA and the Amygdala

Like testosterone and serotonin, MAOA-L might affect impulsive aggression because it affects amygdala reactivity. Brain imaging studies show people with the MAOA-L gene have less activity in the PFC and more activity in the amygdala when they are viewing angry faces. This suggests they may be quicker to anger because of the amygdala’s activity and less able to control their impulsive reaction because of their reduced PFC activity.

Key Study: MAOA and the Amygdala (Meyer-Lindenberg et al.)

The aim of this study was to study brain differences in healthy people with MAOA-L and MAOA-H variants. To do this, they conducted several brain scans and cognitive tasks. Like other studies, they used an fMRI to measure amygdala reactivity to angry and fearful faces. They also used MRI technology to compare brain volumes. The MRI results showed that men with the MAOA-L variant had, on average, an 8% reduction in volume of their amygdalae and in a part of their PFC called the orbitofrontal cortex (OFC). The fMRI results showed they had increased amygdala reactivity and reduced activity in parts of their PFC when viewing angry and fearful faces. The researchers concluded that this data provides neurological explanations for why MAOA-L is linked with impulsive aggression.

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MAOA and Neurotransmission

Let’s get into the synapse for a deeper explanation for MAOA and aggression. MAOA stands for monamine oxidase A. This is a metabolising enzyme that breaks down monoamine neurotransmitters. After monoamines like serotonin bind to a receptor site and send their signal, they are released back into the synapse and then reabsorbed into the presynaptic neuron. Here they are digested by the MAOA enzymes. People with the L (low) variant produce lower levels of the MAOA enzyme and people with the H (high) variant produce higher levels. This means that people with the MAOA-L have higher serotonin activity because there’s less enzyme activity breaking down the neurotransmitters.

MAOA-L influences behaviour because it affects enzyme levels which in turn affect serotonin levels.

But why would more serotonin increase aggression? This seems to contradict the serotonin deficit explanation. One hypothesis is that too much serotonin in the womb and in childhood reduces the brain’s sensitivity to serotonin, so as an adult, serotonin becomes less effective.

About 1/3 of all people have the MAOA-L gene. You may be worried you’ve got the MAOA-L gene and are destined for a life of crime. Don’t panic. Most people with the MAOA-L don’t become violent criminals. It’s only when people with MAOA-L also have had severe child maltreatment (e.g. abuse and neglect) that they become at risk for violent crime.

I’ve done my genetic test to see which variant I have. You can watch the video to see the results on our YouTube channel.

Critical Thinking Concept: Variables and Choice of Research Method

Psychologists can’t conduct true experiments on the effects of specific genes on behaviour. To do this, they would have to genetically modify humans. Twin studies are considered a natural experiment – an experiment where the independent variable is naturally occurring. Meyer-Lindenberg’s study is also a natural experiment because it compares naturally occurring variations in genes – L vs H. Why are natural experiments used to study aggression? Do you think they can show causal relationships?

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3.2 Animal Models: MAOA Knockouts

What is an animal model? What is a MAOA knockout?

Why do psychologists use animal models like MAOA knockouts?

What is one limitation with using MAOA knockouts to study behaviour?

An animal model in psychology is when animals are used to help explain human behaviour. Just as architects create small models of the buildings they’ve designed to show people their ideas, psychologists use animals to represent processes that help explain human behaviour. Most of the time, these are biological processes.

Animal knockouts (aka genetic knockouts) are a specific type of animal model. Psychologists create animal knockouts by genetically modifying animals to have a specific gene removed (i.e. “knocked out”). Experiments are conducted to compare their behaviour to normal animals. The differences in behaviour demonstrate (or model) the influence of a specific gene. For example, psychologists have created MAOA knockout mice – mice with their MAOA gene removed so they don’t produce the MAOA enzyme. Studies show the MAOA knockouts are more aggressive than ordinary mice.

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Key Study: MAOA Knockout Mice and Aggression (Cases et al.)

Researchers genetically modified a group of mice to create MAOA knockouts and used the resident-intruder test to compare their aggression with a control group. They found the MAOA knockouts were more aggressive than a control group of mice. They also measured total bite marks and wounds on mice living in cages with lots of other mice. The male knockouts living in the same cages had more wounds than control mice. They also measured the neurotransmitter levels of serotonin, dopamine and norepinephrine. The knockouts had higher levels of all three monoamine neurotransmitters. This study shows how the MAOA gene is linked with aggression, probably because of its influence on monoamine neurotransmitters like serotonin.

An animal model could be animals used in studies, like an MAOA knockout. The term animal model can also refer to specific tests designed to represent human behaviours, like aggression and depression. How do we know if a rat is depressed? We use animal models of depression like the forced swim test or the tail suspension test – where a rat is dropped in a bucket of water or held upside down by its tail – while psychologists time how long it takes before the animal stops struggling. The quicker the animal gives up, the more depressed it is. In animal models of aggression, the resident-intruder test is used. A resident male rat lives in a cage with a female for a week. Then, the female is taken out and another, slightly smaller, male rat is

A gene is a sequence of DNA. Researchers delete these sequences to create animal knockouts.

MAOA knockout mice are more aggressive than other mice. This could be because of their increased neurotransmitter levels.

placed in the cage. The researchers measure the “attack latency” – how many seconds until the resident first attacks the intruder. The faster the attack, the more aggressive the rat is.

Genetic knockout studies show the value of animals in psychological research – we can manipulate biological factors like specific genes in highly controlled environments. We can also gain precise measurements of behaviours that represent aggression or depression. This provides laboratory experimental evidence to combine with human correlational studies and natural experiments to understand the role of genes in human behaviour.

Critical Thinking Concept: Causality and Reductionism

Psychologists want to test cause and effect relationships between two variables. For example, they want to see if a specific gene like the warrior gene causes aggression. To do this, they must use reductionism – reducing something down to its simplest parts. It doesn’t get much more reductionist than looking at one gene out of a possible 20,000. Psychologists can test this gene by knocking out (i.e. removing or turning off) the MAOA gene in animals and measuring aggression. What is one limitation of using such a reductionist approach to understanding behaviour?

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4. Research

4.1 Biological Reductionism

What is biological reductionism?

Why do psychologists use reductionist approaches in criminology?

What is one limitation of using biological reductionism in criminology?

Reductionism in psychology is when a psychologist reduces complex behaviour to one single, specific cause. Biological reductionism is when that cause is biological. For example, when a biological psychologist uses an MAOA knockout mouse, they are using biological reductionism – they’re focused on a single, specific biological factor (i.e. the MAOA gene) to see its effect on behaviour. Animal models allow psychologists to use a reductionist approach in their research. Using animal models in this reductionist way allows psychologists to study behaviour in ways that are valid, ethical and practical.

Validity

Animal knockout studies allow researchers to completely control the environment and other extraneous variables. For example, in animal knockout experiments, everything is kept consistent between the two groups: the animals are the same age, same breed, and given the same food and water. By keeping all conditions constant except the independent variable (e.g. the MAOA gene), they can draw causal conclusions. When a study is well-controlled and isolates the IV, we say it has high internal validity. A study with lots of uncontrolled extraneous variables has low internal validity.

Ethical

Studies on the brain are very difficult to conduct using laboratory experiments. For example, we could not ethically damage someone’s amygdala or PFC to see the effect. The alternative is a natural experiment, in which you can find people with naturally occurring damage in their brains. However, these studies have lots of extraneous variables, like participant characteristics and their environments. The major ethical guideline in human research is “do no harm.” This is difficult when you’re manipulating people’s biology. This is why it’s arguably more ethical to manipulate animal biology in laboratory experiments than use human participants.

Practicality

“Reductionism is an approach in psychology that seeks to understand complex phenomena by breaking them down into simpler, more manageable components or elements.” (IB Guide).

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Finding participants for your experiments is difficult. It takes a lot of time, effort and money. These are the practical elements of research that psychologists must consider. When studying the MAOA gene in animals, for example, you must go to a prison and find your sample, get them to agree to genetic tests, run the tests in the lab, and then find your MAOA-L and MAOA-H groups. Only after these steps are you able to run your study. Using animal knockouts, on the other hand, is comparatively easy. A researcher can breed their knockout mouse, and then labs all over the world can breed from the original pair. Rats and mice can have up to 11 sets of pups in a year, so you can get heaps of data more easily than with human participants.

Key Study: Brain Lasers in Rats (Han et al.)

A rat’s amygdala is activated when they hunt. This study wanted to see if the amygdala causes this hunting behaviour. To do this, they infected mice with a virus that made their neurons sensitive to blue light. They then created a blue laser light and attached it to the amygdalae of the mice. By turning the light on and off, they could turn the amygdalae on and off. When they turned the laser on, the mice attacked the first object they could see. This included animals like insects and even random objects like a bottle cap. The researchers concluded the amygdala plays a central role in hunting and aggression. Through this reductionist method, the study shows the amygdala’s central role in aggression.

Limitations of Reductionism

The major limitation of biological reductionism is that it overlooks the complexity of human behaviour. For example, if we use reductionism to study a specific part of the brain like the amygdala or the PFC, are we really getting to the root cause of behaviour? We’re overlooking how environmental and cognitive factors shape the brain. Similarly, our genetics are shaped by our environment. Things like stress, abuse and neglect can affect gene expression – the messages

Biological reductionism is when psychologists focus on specific biological factors like individual genes to understand behaviour.

sent from the gene to spark other biological processes, like the production of MAOA. Studies have shown, for instance, that early life stress in animal models reduces expression of the MAOA gene. These examples highlight a major limitation with biological reductionism.

Critical Thinking Concept: Causality, External Validity and Generalisability

The validity of using animals to study causality in humans is debated. This relates to the concept of external validity (aka generalisability) – the extent to which findings from one study can be applied (or generalised) to another context (people, place or situation). In evaluating generalisability of animal studies to human behaviour, I recommend the two Cs: culture and cognition. Findings from animal studies might not apply to humans because we have more sophisticated cognition (ways of thinking) and culture. For example, it might be tempting to conclude from the rat laser study that increased amygdala activation causes aggression. What is one reason why this might not apply to humans? Consider culture and/or cognition.

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4.2 Ethics in Animal Research

What are the Three Rs of ethics

in animal research?

How can psychologists follow the Three Rs? How can following the Three Rs affect validity?

You’ve learned about the benefits of animal studies. However, animal experimentation is contentious. Some argue they’re valuable and worthwhile, while others question their validity and ethicality. The fundamental issue with animal research is that animals cannot provide informed consent. However, some argue the benefit to human life is a valid justification. In response to this debate, psychologists have proposed the Three Rs of ethical animal research: reduce, refine, replace

Reduction: Psychologists should reduce the number of animals used in research. Methods for reducing animals include:

• Using the smallest sample necessary for reliable data.

• Avoiding repeating a study that has already been done.

• Sharing research data with other psychologists.

• Using brain imaging technologies like fMRI instead of post-mortem dissections. This means the same animals can be used for multiple studies.

Refinement: Psychologists should refine the experimental procedures to minimize the harm and improve animal welfare. Methods for refinement include:

• Using anaesthesia for all surgeries and euthanising animals to end unnecessary suffering at the end of the experiment.

• Training all researchers in the proper handling and care of animals.

• Improving the animals’ living conditions (e.g. providing larger cages that are cleaned regularly and reflect their natural social environments).

Because animals can’t give informed consent, the Three Rs provide valuable guidelines for psychologists to conduct ethical research.

Replacement: Where possible, psychologists should replace animals with other methods or other types of animals. These include:

• In silico methods: using computerized or digital methods instead of real animals (“in silico” means in or on a computer).

• In vitro methods: using only a small part of the animal to understand the bigger picture. For example, removing individual brain cells and keeping the animal alive instead of dissecting a whole brain.

• Replacing vertebrates with invertebrates. For example, using sea slugs instead of rats.

Key Study: Rat fMRI (Brydges et al.)

The aim of this experiment was to see how fear and early life stress affects the amygdala in rats. The researchers used Pavlovian fear conditioning to train the rats to fear a blue light. After five days of conditioning, their brains were measured using special fMRIs. The researchers measured their brain activity and found the rats’ amygdalae were activated when they saw the blue light. They also found that animals who suffered early life stress (e.g. as pups being forced to swim in a bucket of water for 10 minutes) had greater activity in their amygdala than control rats. This study shows how fMRI can be used to measure brain activity during learned behaviours like conditioned fear. It also provides an animal model for disorders like PTSD – early life stress changes amygdala response to conditioned fears.

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You can read more about this study on our blog “Rats in an fMRI?”

The Three Rs are not new. In fact, Russell and Birch proposed the first 3 Rs way back in 1959. More recently, a fourth has been proposed – responsibility. This principle underlines the first three and focuses on how psychologists should take responsibility for the status of animal research. This includes the status of the animals used, the scientific status of their research and the social status of animal studies. Methods for taking responsibility include:

• Animal status: Psychologists can maintain the animal’s status by ensuring they are cared for properly and ethically. Some argue they should also treat animal research as a privilege, not a right.

• Scientific status: Psychologists are responsible for carefully designing scientific studies that will produce valid and meaningful results.

• Social status: Psychologists are responsible for educating the public about animal studies, their potential applications and how psychologists are maintaining animal welfare.

I have no doubt that the debate about using animals in psychological research will go on for at least another 50 years. What do you think?

Critical Thinking Concept: Balancing Ethicality and Validity

Validity is important when establishing causality. You need to control for extraneous variables to show A causes B, and nothing else. However, psychologists must also consider the ethicality of their studies. Sometimes, following ethical guidelines like the Three Rs can jeopardize the validity of the study. Using one of the animal studies you have learned about, can you explain how following one or more of the Three Rs might affect the validity (or reliability) of an animal study?

Review

In this chapter, you’ve been introduced to the most important biological factors in the biological approach to understanding human behaviour: the brain, chemical messengers and genetics. You also learned about methods used to study these factors, like animal models, brain imaging, experiments and correlational studies. In doing so, you have covered nearly every topic in the biological approach needed for Paper 1, Questions A and B. If you found this content tough, you will review them again in the Depression chapter and cover the missing topic – the diathesis-stress model.

Paper 1 SAQs (1A + 1B): Approaches

Study Tip: If you found the critical thinking concepts and research methods too complicated, try re-reading them after you’ve conducted the class practicals and the IA. They will make more sense by the end of the course.

You should be able to write an SAQ explaining the following learning outcomes (Qu. 1A) and apply this content to a new context (Qu. 1B). There’s space for you to choose your example for Qu 1A - a real-world example or a key study.

Biological Approach Learning Outcomes for Paper 1 Section A + B

Animal research and animal models

Explain the value of animal research in the study of human behaviour.

Explain ethical considerations in the use of animals in research.

Biological reductionism

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Brain imaging techniques

Chemical messengers

Neurotransmission

The strengths and limitations of a reductionist approach to the study of behaviour.

Explain the value of using one or more brain imaging techniques in investigating human behaviour.

Topic Example: Key Study or Real World

• MAOA knockouts and aggression (Cases et al.)

• Brain lasers in rats (Han et al.)

• Rat fMRI (Brydges et al.)

Internal vs external validity in animal studies

fMRI or MRI

Explain how one or more chemical messengers can influence human behaviour. (e.g. neurotransmitters or hormones).

Explain the process of neurotransmission and how it can affect human behaviour.

Genetic inheritance Using one example, explain the extent to which human behaviour may be inherited.

Neuroplasticity

Explain the process of neuroplasticity and the role of environmental factors on brain development.

Testosterone or serotonin

Serotonin

MAOA gene

ACEs and the hippocampus and amygdala.

• fMRI on abuse and the amygdala (McCrory et al.)

• MRI of criminal brains (SaiousTurner et al.)

• Testosterone and the braom (Radke et al.)

• Serotonin and the brain (Passamonti et al.)

• Real world example – glutamate and blackouts

• MAOA and the brain (Meyer-Lindenberg et al.)

• Abuse and the amygdala (McCrory et al.)

MAOA knockouts

Three Rs

Paper 1 Essay Context: Human Relationships

Some content in this chapter is also relevant for learning outcomes in the context of “Human Relationships.” In particular, the explanation of how one or more chemical messengers plays a role in human relationships. In this chapter, we looked at the role of testosterone in preparing the amygdala to deal with a threat, which leads to aggression. We also looked at the role of serotonin in increasing connectivity between the PFC and the amygdala to help us regulate our emotions during conflict. You could use what you’ve learned in this chapter to come up with strategies to improve relationships by reducing aggression, although content for this topic is covered in “Couples.”

The essay will ask you to discuss these topics in relation to one of the six concepts. There is guidance in the exam preparation section on how to review for these questions