3 The biological approach to understanding human behaviour
Wernicke area: the part of the brain that processes the meaning of language, located in the rear of the brain.
Information obtained from those pioneering cases was foundation material for mapping the brain. Taking part in a conversation activates both the Broca area and the Wernicke area – two very different parts of the brain – and also the very complex connections between them, as well as the auditory nerves and speech muscles.
Wernicke’s aphasia: impaired ability to understand speech, yet able to produce speech.
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Wernicke (1874) worked on cases that complemented those of Broca: individuals who, following a stroke, were still able to talk but could not understand what was being said. Autopsies after the deaths of those patients showed that the part of the brain damaged by the stroke was the left posterior superior temporal gyrus.The area of the brain that gives the function to be able to understand speech is named the Wernicke area. Its non-functioning is referred to as Wernicke’s aphasia.
Case study: HM
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However, the case of HM indicates that functions of the brain do not appear to be confined to single locations. HM fell off a bicycle at the age of seven and suffered an injury which was believed to be causing his subsequent, continued serious epileptic seizures. In 1957, doctors removed the tissue from the temporal lobe of the brain (there was no effective drug treatment at the time), including much of the hippocampus. Following the operation, HM could recall information acquired early in life, but he could not form new memories; a case of anterograde amnesia. HM’s brain was scanned in 1997, showing that the areas that had been damaged included the hippocampus and amygdala regions. The fact that HM’s memory functioned at all indicated that memory functions are more widely distributed throughout the brain than previously thought, and not just in these two regions.
Anterograde amnesia: being unable to form new memories after brain damage, but still able to recall memories made before the brain damage.
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Major breakthroughs in attempting to locate brain functions began in the 1960s with the innovation of electronic brain-scanning techniques. This made it possible for researchers to see images of the soft tissue inside the skull while the person was alive. No autopsy was needed. Electroencephalography (EEG) began to be developed in the 1950s, which included EEG topography that made it possible to study the electrical activity taking place across the surface of the brain. Computerised tomography (CT) was introduced in the 1960s and 1970s. In practice, this focusing of X-ray beams to give an overall static picture of the brain is used to identify lesions (damage to the brain) and atypical structures within the brain. It was succeeded by the higher resolution, second-generation magnetic resonance imaging (MRI), which in turn is continuing to give way to third generation, very expensive positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). These two systems not only give details of the brain as it is, but are able to trace activity within the brain, including which parts of the brain are operating when a person is performing a specific task.
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PET and fMRI have shown that the different patterns in brain activities are extremely multidimensional, with various parts of the brain being coordinated to varying degrees of intensity. The extremely complex brain mapping rules out, for the most part, a single part of the brain being exclusively responsible for a specific function. The range of brain-scanning techniques continues to develop. Each has its own strengths and limitations. Apart from suitability for the particular task, their use is constrained by cost and availability.
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These electronic methods are among the most common techniques used today in researching the way the workings of the brain influence behaviour, and their use will be exemplified in the study below. However, observations from autopsy, stroke, accident victims and brain surgery patients have also contributed to understanding the brain and behaviour, as exemplified by the case study of HM.
Research study: Harris and Fiske (2006) Like many modern research studies of the workings of the brain, this study on defining the parts of the brain that determine attitudes and resultant behaviours towards others, used fMRI. This highly complex technology uses a magnetic field and radio signals to observe a specific process taking place in the blood flow within the different parts of the brain. The process takes place in the haemoglobin (the protein content of the blood) that carries and releases oxygen. The more active the part of the brain, the more oxygen it uses, and the greater the amount of oxygen that will be released. The fMRI scanner sends a series of radio-frequency magnetic pulses that reorientate the hydrogen atoms in the brain. The speed at which they come back to where they were is a measure of the degree of oxygenated haemoglobin in that part of the brain.
© Cambridge University Press 2018
Amygdala: the part of the brain that integrates basic emotions, emotional behaviour and motivation. Electroencephalography (EEG): a brain-scanning machine where a large number of electrodes are attached to the head, making it possible to record impulses from the top layers of the brain. Computerised tomography (CT): scanning technique in which ionised dye is injected in the blood to highlight specific brain tissue. The tissue is then scanned to create an image. Lesion: a structural alteration to tissues or organs caused by disease or injury. Magnetic resonance imaging (MRI): a brain-scanning method that monitors the electromagnetic energy released by the brain after it has been exposed to a magnetic field. Positron emission tomography (PET): an electronic technique that images processes in the brain. Its mechanism is based on the injection of radio-active material into the bloodstream, and the monitoring of the decayemitted positrons in the brain.
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