Understanding and Maintaining Memory | Billie Enz

Understanding and Maintaining Memory

Billie Enz

Making a memory is a multi-step process that we engage in constantly. From taking in sensory information to interpret your environment, to learning new information such as ever-changing technologies, to recalling the name of an old classmate requires multiple systems in our brain to work together seamlessly. This chapter is designed to provide readers with a greater understanding of the brains intertwined organization and functions, a deeper appreciation of the brains’ memory systems, and finally a discussion of science-based strategies for maintaining memory and brain health.

I. Interconnected Brain Organization and Functions

We are living in an exciting age of neurological discovery. New technologies have allowed researchers to observe the living brain’s function. These data provide researchers with a better way to understand the organization and functional operations of the brain. They have revealed that the brain is a highly organized, complex, multi-functional organ, and nearly all components play a role in sensory intake, memory storage and retrieval. To understand how our memory systems work, it is important for the reader to have a basic grasp of terminology and architecture of the brain.

The Hemisperes and Corpus Callosum: At the most basic structural level, the brain is divided into two hemispheres (italicized words are illustrated in the Figures) that are connected by the corpus callosum, a band of nerve fibers which carries messages between the hemispheres integrating information to process motor, sensory, and cognitive signals simultaneously. The brain’s right hemisphere controls the muscles on the left side of the body, while the left hemisphere controls the muscles on the right side of the body. Each hemisphere performs a fairly distinct set of operations. In general, the left hemisphere is dominant in language: processing what we hear and handling most of the duties of speaking. The right hemisphere is mainly in charge of spatial abilities, facial recognition and processing music. (1)

Enz | From the Lectern

The right and left hemispheres are connected by the corpus collosum.

The Lobes and Cerebellum: Each hemisphere is divided into four distinct regions called lobes. It is important to remember that no part of the brain is an isolated component that can function without information from other parts of the brain and body. While each lobe has been associated with specific tasks, they are subdivided into interlocking networks of neurons that coordinate overlapping and complex tasks, such as talking, which concurrently requires memory, forethought, and motor coordination of tongue and lips. (Box - Neurons and Neural Networks). All four lobes comprise what is referred to as the cerebral cortex. (2) The following describes the major functions of each lobe. Notice that each lobe plays a role in learning and memory creation, storage, and recall.

The Lobes and Cerebellum: the lobes extend and cross over both hemispheres.

• Frontal lobes manage higher level executive functions, which include a collection of cognitive skills such as working memory,

attention span, capacity to plan, organize, initiate, self-monitor and control one’s actions to achieve a goal. Towards the back of the frontal lobe is the motor cortex, which is responsible for planning and enacting voluntary movement including speech production in the Broca’s Area. (3)

• Parietal lobes contain the primary sensory cortex, which interprets and remembers sensation such as touch, pain, pressure. Behind the primary sensory cortex is a large association area that interprets fine sensation such as texture, weight, size, and shape. The parietal lobe is also responsible for sensory integration, integrating visual, auditory, somatosensory, olfactory and taste, which enables us to encounter our world as a unified experience. In other words, when we have our morning coffee, we can simultaneously taste and smell the rich flavor, see and hear the coffee pouring into our cup, and feel the warmth as we swallow. The parietal lobe also plays a significant role in allowing us to recall these sensations. (4) • Temporal lobes: The left side of the temporal lobe contains Wernicke’s Area which is concerned with interpreting/processing/ comprehending auditory stimuli. As we hear the myriad of sounds in our environment, the Wernicke’s area sorts, recognizes, and interprets the meaningful units of our native language. (5) Interestingly, the temporal lobe is also associated with supporting visual recognition of objects, places, and faces. Finally, the temporal lobe is home to the limbic system, which is responsible for our ability to pay attention, make and recall memories, feel emotions, and respond appropriately. • Occipital lobes are the seat of the brain’s visual cortex, which allows us to see and process stimuli from the external world, and assign meaning and remember visual perceptions. The occipital lobes gather information from the eyes; this occurs when light proceeds through the pupil. As the light progresses through the pupil, it strikes different types of photo-receptor cells, called rods and cones on the retina. Light stimulates these photoreceptors, which then fire an impulse through the optic nerve, which carries the information instantaneously to the occipital lobe at the back of the brain, where it’s processed and perceived as a visible image. (6) • The Cerebellum is located at the base of the brain and receives information from the balance system in the inner ear, spinal cord, sensory strip, and the auditory and visual systems. The cerebellum

Enz | From the Lectern

Enz | From the Lectern integrates information to coordinate and fine-tune motor activity and predicts and corrects errors in timing. It is also involved in motor memory and learning, from simple motor coordination such as managing food utensils to complex ballet or basketball maneuvers, to autonomic skills such as word processing and bike riding. (7)

The Limbic System lies deep within our brain between the two hemispheres of the temporal lobe. The limbic system is responsible for memory and emotion, motivation, behavior, and various autonomic functions, such as the sensation of hunger and thirst and the ability to detect odor through the olfactory bulbs. The last four decades of research have provided a wealth of detailed information on the connectivity and functions of the limbic system, and this knowledge continues to evolve. (8)

The Limbic System: This simple diagram of the limbic system gives emphasis to the main structures known to make up this brain region.

• The thalamus continuously monitors the external environment for input. As massive amounts of sensory information flood the waking brain, the thalamus functions as a relay station, determining what sensory information will receive further focused attention and potential action, and as important, what sensory input will be ignored.

As a regulator of sensory information, the thalamus also controls sleep and plays a major role in regulating arousal, level of awareness, and activity. (9) • The amygdala may be best known as the part of the brain that drives the so-called “fight, flight or freeze” response. While it is often associated with the body’s fear and stress responses, it also plays a

pivotal role in memory, particularly the storage of memories associated with emotional events. (10) Both the thalamus and amygdala are constantly monitoring the external environment for any threat to our survival.

• The hippocampus is critical to the storage of memory. The hippocampus evaluates information, determining if something is worth remembering (long-term memory) and then where to file it so that this memory can be retrieved. The hippocampus is essential in forming new memories and connecting emotions and senses. The hippocampus also plays a role in consolidating memories during sleep. In addition, the hippocampus appears to serve as a navigator that helps with spatial orientation—in other words, helping us know where we are and how to get from here to there. (11) • Olfactory bulbs work as odors enter through the nostrils and are absorbed by the nasal mucosa. Information about the scent is processed by the neurons in the olfactory cortex which identifies it. The olfactory sense is the only sense to bypass the thalamus and register information directly with the hippocampus. For example, just the smell of spoiled food can trigger actual nausea and vivid memories of what happened the last time we consumed something that smelled like that. This suggests that the olfactory system once played a vital role in human survival. (12)

• The hypothalamus is constantly monitoring the body’s internal environment for input. The hypothalamus produces hormones that control thirst, hunger, body temperature, sleep, moods, sex drive, and the release of hormones from various glands, primarily the pituitary gland. The hypothalamus regulates homeostasis in the human body, making sure that everything in our bodies is always in balance. For example, if you have had too many salty foods, the hypothalamus gives you a thirst sensation—therefore causing you to drink water to put your system back in balance. (13)

A review of the main components of the brain reveals the whole is greater than the sum of its parts. It is important to remember that no part of the brain is an isolated element that can function without information from other parts of the brain/body. While each component has been associated with specific tasks, they are subdivided into interlocking networks of neurons (brain cells) that coordinate overlapping and complex tasks. Likewise, the same can be said about memory. Nearly all the brain components discussed work together to form a multi-layered system of memory.

Enz | From the Lectern

Enz | From the Lectern

II. Interconnecting Memory Systems

Memory refers to the processes that are used to encode, store, and later retrieve information. Memory can be broadly divided into three interconnected systems: sensory memory, working memory and long-term memory.

Memory Systems. Memory can be broadly divided into three interconnected systems: Sensory memory, Working memory and Long-term memory.

• Sensory Memory During every waking moment of our life, sensory information is being perceived by sensory organs (eyes, ears, skin, taste buds, olfactory bulbs). Sensory memory is brief, just a few seconds, allowing vast amounts of information to be processed from potentially all sensory organs, simultaneously. Though brief, sensory memory allows us to retain impressions of sensory information after the original stimulus has ceased. For example, think of a firework display, while the experience is brief, we can easily recall the booming and whizzing sounds, the beautifully multi-colored explosions of light of various sizes and shapes, and the lingering smell of gun powder in the air. As the sensory information comes in, the thalamus (in the limbic system) plays a critical role in scanning and categorizing the sensory data to help determine what information is important and should receive attention and what information is immediately forgotten. At the same time, the amygdala is evaluating the incoming sensory information, in the context it is occurring, for risk. If these sensory inputs are coming at a celebratory event, it is expected and viewed as safe and exciting; however, should these same fireworks occur unexpectedly (while you are shopping at the grocery store) then they might be considered a danger. (14)

• Working memory is often referred to as short-term memory. Working memory is a temporary store for a subset of sensory information to which attention has been applied. Working memory allow for temporary storage and manipulation of information such as doing mathematical calculations or reading a sentence. Working memory has a limited capacity, typically described as seven bits of information (plus or minus two), for a short duration of approximately 20 to 30 seconds. The capacity of working memory can, however, be extended by the process of chunking, in which several items are grouped together into a single cognitive unit, for example, a phone number. The duration of working memory can also be extended by the process of rehearsal in which items are repeated to keep them in working memory for longer than 30 seconds. (15) • Long-term memory is unlimited in capacity and potentially permanent in duration. Long-term memory can be divided into explicit memory sometimes called conscious or declared, and implicit memory sometimes called unconscious or non-declarative. (16)

Long-term memory can be subdivided into two broad categories Explicit and Implicit.

• Explicit memories are conscious memories that can be recalled and described (declared). They include episodic memory. These memories create the autobiographical story of one’s life such as a first kiss, graduating from school, weddings, first job, etc. Since episodic memories are often laden with emotions they are easily recalled. (17) Semantic memory includes general knowledge that one learns in school or on the job. People tend to store new information more readily on subjects that they already have prior knowledge about, since the new information has personal relevance and can be mentally connected to related information that is already stored in their long-term memory.

Enz | From the Lectern

Enz | From the Lectern • Implicit memories are outside conscious awareness and include procedural memories, such as how to ride a bicycle, type, drive a car, or play an instrument. While initially learning these skills requires a great deal of attention and effort, once learned, these actions are done routinely without much cognitive energy. Implicit memories also include emotional conditioning, often referred to as bias. We have a bias when, rather than being neutral, we have a preference or aversion to people, places, and things. For example, most humans have negative feelings towards spiders, insects, and snakes. However, humans can form bias towards individuals of a different color or culture without conscious knowledge. (18)

Each type of memory is important and serves different purposes. Sensory memory allows us to perceive the world. Short-term memory allows us to process and understand information in an instant. Our most treasured and important memories are held in long-term memory. Our integrated memories systems make us who we are as individuals.

III. Making Memories: Encoding, Storage and Retrieval

Memories are made in three distinct stages. It starts with encoding. Encoding is the way external stimuli and information make their way into your brain. The next stage is storage, either momentarily or permanently. The final stage is recall. Recall is our ability to retrieve the memory we’ve made from where it is stored.

Encoding is the first step in creating a memory. It’s a biological phenomenon beginning with sensory perception. Consider, for example, the memory of your first romantic kiss. When you met that person, your eyes/occipital lobe registered their physical features, such as the color of their eyes and hair. Your ears/temporal lobe heard their voice. You noticed the scent of their skin via your nose/olfactory system. You felt the touch and warmth of their lips through your skin/sensory strip in your parietal lobe. Each of these separate sensations first travel to your thalamus which evaluates and prioritizes the sensory information. Next, if the experience is deemed important, the separate sensory perceptions are integrated into one single experience in the parietal lobe. (19) Although a memory begins with perception, it is encoded and stored using a vast neural network communication system via electrical and neural chemical signals.

Neurons (brain cells) are the fundamental units of the brain and nervous system. The cells are responsible for receiving sensory input from the external world, for sendNeural Networks: Neurons are the ing motor commands to fundamental units of the brain. muscles, and for transforming and relaying the electrical and neuro-chemical signals. The electrical signals are carried though the axon, a thin fiber that extends from a neuron Each axon is surrounded by a myelin sheath, a fatty layer that insulates the axon and helps it transmit signals over long distances between cells.

The electrical firing of a pulse down the axon and to the synaptic gap triggers the release of chemical messengers called neurotransmitters. These neurotransmitters diffuse across the spaces between cells, attaching themselves to neighboring cells dendrites. Dendrites are designed to receive the electrochemical communications from neighboring neurons. Dendrites resemble a tree-like structure, forming projections that become stimulated by linking other neurons. Each brain cell can form thousands of links, giving a typical brain about 100 trillion fluid synaptic connections. (40)

Networks organize themselves into groups that specialize in different kinds of information processing. As one brain cell sends signals to another, the synapse between the two become stronger and faster. Thus, with each new experience, your brain slightly rewires its physical structure. It is this flexibility, which scientists call plasticity, that can help your brain rewire even if it is damaged. (41)

To properly encode a memory, you must first be paying attention. Let’s consider the “first kiss” example, while the kiss occurred there were dozens of sensory stimuli occurring concurrently; the light, cool breeze, the smell of pizza in the background, the sound and sight of people walking by, etc. Since you cannot pay attention to everything all the time, most of what you en-

Enz | From the Lectern

Enz | From the Lectern counter every day is simply filtered out, and only a few stimuli pass into your conscious awareness. What scientists aren’t sure about is whether stimuli are screened out during the sensory input stage or only after the brain processes its significance. What we do know is that how you pay attention to information may be the most important factor in how much of it you remember. (20)

Storage. Once a memory is created, it must be stored (no matter how briefly). There is a progression: first in the sensory stage; then in short-term memory; and ultimately, for some memories, in long-term memory. Since there is no need for us to maintain everything in our brain, the different stages of human memory function as a filter that helps to protect us from the flood of information that we’re confronted with daily. Hence, most sensory and short-term memory are forgotten and decay rapidly. (21)

The hippocampus is responsible for analyzing the experience (and all contributing sensory inputs) to determine if it is important enough to become part of long-term memory. The various bits of sensory information are then stored in different parts of the brain, for example visual information in stored in the occipital lobe while auditory information is stored in the temporal lobe. How these bits and pieces are later identified and retrieved to form a cohesive memory is still being studied. (22)

Important information is gradually transferred from short-term memory into long-term memory. Information is most likely to be retained if it has emotional force (joy, fear, sadness, disgust, and anger). Another way a memory is retained is through repetition. The more the information is repeated, used, or practiced, the more likely it is to eventually be retained in long-term memory. (23) When long-term memories form, the hippocampus retrieves information from the working memory and begins to change the brain’s physical neural wiring to consolidate the new long-term memory. Consolidation occurs during sleep, particularly during REM (rapid eye movement). Longterm memory can store unlimited amounts of information indefinitely. (24)

Retrieval. Once information has been encoded and stored in memory, it must be retrieved to be used. Memory retrieval is the process of accessing stored memories. There are many factors that can influence how memories are retrieved from long-term memory. For example, a memory may be initiated through a sensory stimulus: Walking through the shopping mall the aroma of warm buttery, cinnamon bread lingers in the air. Immediately you are transferred back to your grandmother’s kitchen and for a moment you are in her presence, you can hear and visualize her, in her kitchen in 1958.

The sensory experience that triggers a rush of episodic memories, is called the Proustian moment (named after the French author, Marcel Proust). This is an example of the power of olfactory memory recall. The sense of smell, unlike other senses, by-passes the thalamus and immediately triggers the amygdala and hippocampus and instantaneously a whole orchestra of memories flood to the conscious mind. This type of memory is usually associated with emotional content when it was encoded, and these same emotions will often arise when the memory is prompted by the sensory stimulus. (25)

Explicit memory retrieval, where episodic and/or semantic memories are recalled, usually occurs when you want to consciously remember something, such as the name of someone or answers to questions posed to you. Longterm memory retrieval requires revisiting the nerve pathways formed during the encoding and storage of the memory. How quickly a memory is retrieved usually depends upon the strength of neural pathways formed during its encoding, for example if the event or learning experience provoked some type of emotion, there is a strong probability memory will be easily recalled. (26)

However, “all” of us have experienced challenges with memory recall, for instance the “key” conundrum, or tip-of-the-tongue moments. Forgetfulness is a normal part of aging as shrinkage in the frontal lobe and hippocampus, which are areas involved in higher cognitive function and encoding new memories. However, for most people overall memory remains strong throughout their 70s. In fact, research shows that the average 70-year-old performs as well on certain cognitive recall tests as do many 20-year-olds, and many people in their 60s and 70s score significantly better in verbal intelligence than do younger people. (27) A great deal of memory variability in older individuals depends on brain/body health.

IV. Maintaining Brain Health and Memory Systems

Brain health refers to how well a person’s brain functions across several areas. Including: • Cognitive health: how well you think, learn, and remember • Motor function: how well you control physical movements, including balance • Emotional function: how well you interpret and appropriately respond to others • Tactile function: how well you respond to sensations of touch

Though brain health can be affected by injuries like stroke or traumatic brain injury, depression, and dementia diseases, there are many lifestyle

Enz | From the Lectern

Enz | From the Lectern changes that make significant difference for maintaining brain and body health. (28) These include:

Annual Medical Exams. Your physical health impacts your cognitive health. Schedule annual health screenings to proactivity detect problems such as diabetes, high cholesterol, and high blood pressure which contributes to cognitive decline. Recent clinical research revealed lowering blood pressure reduces the risk for mild cognitive impairment, which is a risk factor for dementia. (29) During your exam you should also consult with your doctor about your medications (including over the counter drugs) as they may have possible side effects on memory, sleep, and brain function.

Sleep is critical factor for brain/body health. Your brain stays remarkably active while you sleep. (30) Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake. In addition to repairing damage caused by our busy metabolism, sleep replenishes dwindling energy stores and even grows new neurons. (31)

Nutrition. A healthy diet reduces the risk of many chronic diseases such as heart disease or diabetes and plays a significant factor in brain health. Recent studies have focused on fruit and vegetable intake and its impact on cognitive function. Research findings have revealed that adequate consumption can prevent cognitive decline, while low intake is associated with increased cognitive decline. (32)

Physical Activity. Studies consistently link ongoing physical activity with benefits for the body, brain, and cognition. Research has revealed exercise stimulates the brain’s ability to maintain old network connections and make new ones that are vital to cognitive health (33) Other studies have shown that exercise increases the size of the hippocampus which is important to memory and learning. Research also reveals that aerobic exercise, such as brisk walking or social dance, is more beneficial to cognitive health than nonaerobic exercise. (34, 35) In addition, studies reveal that the more time spent doing a moderate level of physical activity, the greater the increase in brain glucose metabolism—or how quickly the brain turns glucose into fuel—which may reduce the risk for developing Alzheimer’s disease. (36)

Social interactions. Our brains need socialization. We need interactions and engagement with others to stay mentally active and emotionally connected throughout our lives. From the day we were born social interaction has been a major part of cognitive development. We learn how to speak, interpret, and express emotions, and expand our knowledge from relationships and interactions with parents, siblings, friends, and teachers. As we grow older, socialization is just as important. Building social networks and participat-

ing in social activities keeps your mind agile and improves cognitive function. Consistent socialization can even help prevent mental decline and lower the risk of dementia. (37)

Learning Challenges. Continually learning something new has been found to stimulate greater neuron generation and neural network connections in the brain. Neurons are responsible for sending information throughout the brain and when this is improved, it positively effects memory, attention, thinking and reasoning skills. (38) Fortunately, the concept of “learning something new” is extremely broad, for example academic coursework, learning a second language, acquiring skill to optimize the use of technology, new hobbies such as playing an instrument, singing in a choir/chorus, playing chess, or quilting, to more physical skills such as social dance, yoga, or golf. Numerous studies also revealed that when the brain is learning something new, the body is also benefitting, for example reducing stress levels, slowing heart rates, and easing tension in their muscles. And lower stress has wide ranging benefits for seniors’ cardiovascular health, decreasing blood pressure and reducing the risk of a stroke or heart attack, boosting immunity, and lowering levels of depression. Clearly, humans are meant to be learning and socializing throughout their lives. (39)

The brain is the most complex part of the human body and yet our brain relies on the health of the whole body for optimal wellness. This three-pound organ is the seat of intelligence, interpreter of the senses, initiator of body movement, and controller of behavior. The brain is the source of all the qualities that define our humanity. Knowledge of how the human brain is organized and how is components function as a complex system is critical to understanding memory systems. Hopefully this new information provides motivation to the reader to maintain a healthy brain and body throughout their lives.

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Enz | From the Lectern

Enz | From the Lectern

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Enz | From the Lectern

Enz | From the Lectern Schuster (2021).

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Enz | From the Lectern

I think that intelligence is such a narrow branch of the tree of life - this branch of primates we call humans. No other animal, by our definition, can be considered intelligent. So intelligence can’t be all that important for survival, because there are so many animals that don’t have what we call intelligence, and they’re surviving just fine.

Neil deGrasse Tyson