Brain Structure (Edexcel A-Level Psychology): Revision Notes
Brain Structure
Historical overview
Understanding the relationship between brain structure and behaviour has developed gradually over thousands of years. Ancient civilizations possessed basic knowledge of brain anatomy and function.
Early surgical interventions
Archaeological evidence demonstrates that trepanning (also known as trephination) was practised in connection with migraines and epilepsy around 10,000 years ago. This surgical procedure involved drilling a hole into the skull to address problems related to the brain's surface. The discovery of trepanned skulls from this period indicates that humans have long recognised the brain's role in various conditions.
The practice of trepanning represents one of the earliest known forms of neurosurgery, providing evidence that ancient civilizations recognized a connection between the brain and various medical conditions, even if they didn't fully understand the mechanisms involved.
Development of brain mapping
The ancient Greek physician Hippocrates (born 460 BC), often regarded as the father of medicine, recognised the importance of brain injuries and proposed that different sides, or hemispheres, of the brain served distinct functions. However, understanding of the brain's specific role in governing behaviour remained limited until the early 19th century.
In the early 1800s, Franz Joseph Gall introduced phrenology, which attempted to link personality traits and character to the physical structure of the skull. Although this 'science' was ultimately discredited, it represented an early attempt to establish connections between brain anatomy and behaviour. Phrenology falsely claimed that character could be determined by mapping bumps on the skull, but it did contribute to the broader idea that behaviour was somehow linked to brain structure.
The case of Phineas Gage
One of the most influential early cases demonstrating the brain's role in regulating behaviour occurred in 1848. Phineas Gage, a railway worker in the mid-western United States, suffered a severe accident when a tamping iron (used for pushing explosives into drilled holes in rock) was propelled through his face and skull. The iron rod passed through the front part of his brain, exiting through the top of his head.
Historical Case Study: Phineas Gage
Remarkably, Gage survived for 11 years following the accident. However, his personality underwent a dramatic transformation:
Before the injury:
- Described as reliable and responsible
- Exhibited normal social behaviour
After the injury:
- Became irresponsible and aggressive
- Displayed poor impulse control
Medical examination revealed that the damage had occurred specifically to his prefrontal cortex, leading physicians to conclude that this brain region played a crucial role in regulating character and behaviour.
Issues with case study generalisation
Single case studies like Phineas Gage present significant challenges for scientific generalisation. The outcome may result from unique individual variables, meaning that others with similar damage might respond differently. Gage's specific behavioural changes may have been influenced by his individual reaction to the facial disfigurement he suffered alongside the brain injury.
Without confirming evidence from multiple similar cases across different circumstances, the findings cannot be considered fully reliable or generalisable. Psychology requires convergent evidence from various sources to establish reliable patterns, and when sufficient similar cases demonstrate consistent findings, the conclusions become more robust.
Brain structure and lobes
The human brain consists of two symmetrical halves called hemispheres - one left and one right. Each hemisphere contains four distinct regions called lobes, making eight lobes in total across both hemispheres:
- Frontal lobe: located at the front part of the brain (anterior position)
- Parietal lobe: situated at the top area of the brain
- Temporal lobe: positioned at the side and behind the ears
- Occipital lobe: found at the back of the brain
Early neurological research, particularly through the work of Paul Broca (a French neurosurgeon in the 19th century), helped identify specific functions of these regions. Broca's most notable case study examined a patient known as 'Tan' (named for losing the ability to say any word except 'tan'). Post-mortem examination revealed damage to an area in the lower part of the left frontal lobe. This region, subsequently named Broca's area, is responsible for motor control involved in speech production.
Broca's Area vs Wernicke's Area
Broca's area (frontal lobe): Controls speech production - damage means individuals can understand speech but cannot articulate responses.
Wernicke's area (temporal/parietal junction): Controls speech comprehension - damage means individuals can produce speech but it becomes meaningless, superficially sounding like speech but essentially being nonsense.
Another key area identified early in neurological research is Wernicke's area, named after German neurologist Carl Wernicke who worked in the late 19th century. Located at the rear of the left temporal lobe where it joins with the parietal lobe, Wernicke's area is involved in understanding speech. When patients experience damage to this region, they can typically produce speech but it becomes meaningless - superficially it sounds like speech but is essentially nonsense, indicating problems with language comprehension.
Lesion studies and modern research
Over the years, psychologists have constructed functional maps of the brain using research methods such as lesion studies - investigations examining the effects of damage to specific brain areas on behaviour. Historical research, such as studies on the hippocampus in memory (covered elsewhere in this specification), relied heavily on these approaches. With modern neuroimaging techniques, the task of understanding links between brain areas and behaviour has become more accessible, as researchers no longer need to rely solely on post-mortem examinations or naturally occurring brain damage.
Aphasia refers to a disturbance in the comprehension or production of language caused by brain dysfunction or damage, such as occurs following a stroke. These conditions have provided valuable insights into how different brain regions contribute to specific behavioural functions.
Explaining aggression through brain structure
The Phineas Gage case provided early evidence that damage to the frontal lobes appeared to increase aggressive behaviour. This represented one of the first research findings suggesting a possible biological basis for aggression.
Animal studies of aggression
Investigating the biological structures underlying aggression in humans poses ethical challenges, as experimental damage to precise brain areas cannot be justified. Consequently, typical studies examining the biological structures involved in aggression have used laboratory animals, particularly rodents and cats.
Research has identified three distinct and specific types of aggressive behaviour in these animals:
- Offensive behaviour: physically attacking another animal
- Defensive behaviour: shown in response to threat or attack
- Predatory aggression: attacking another species to obtain food
Brain region activation and aggression types
Lesions (damage, either accidental or deliberate, causing areas of the brain to die) or stimulation (artificial activation of brain areas, often using electrodes producing small electrical charges) to different brain regions have been shown to activate behaviour associated with specific types of aggression:
Brain Regions and Aggression Types in Cats
Research by Flynn, Vanegas, Foote and Edwards (1970) demonstrated specific brain region-aggression relationships:
- The medial hypothalamus produces offensive behaviour when stimulated
- The dorsal hypothalamus produces defensive behaviour when stimulated
- The lateral hypothalamus results in predatory behaviour when stimulated
Brain areas associated with aggression
The midbrain
The midbrain contains a region called the periaqueductal grey matter (PAG), which links the amygdala (discussed below) and the hypothalamus to the prefrontal cortex. This area plays a coordinating and integrating role in behavioural responses to perceived internal and external stressors such as pain and threat.
Studies examining lesions to the PAG in rats that have recently given birth demonstrate increased aggression when the rats are confronted with potential threat in the form of unfamiliar male rats being introduced to their cage (Lonstein and Stern, 1998). This suggests the PAG is involved in modulating defensive aggressive responses.
The amygdala
The amygdala serves as the centre for emotions, emotional behaviour and motivation. It integrates internal and external stimuli, and every sensory modality has an input to the amygdala. When combined, these inputs can produce an instinctive feeling or reaction to the environment that may include aggression. The prefrontal cortex also connects to the amygdala, and it is this connection that may lead to the expression of aggressive behaviour.
The hypothalamus
The hypothalamus plays a role in maintaining homeostasis (the process that maintains stability of the human body in response to changes in external conditions) through the regulation of hormones - chemicals produced by glands which are used to signal between organs and tissues. This includes hormones that regulate sexual function. The production of testosterone (the principal male sex hormone and an anabolic steroid) is linked to aggressive behaviour in males through its connection to the hypothalamus. The role of testosterone and other hormones in aggression is explored in more detail in the hormones section of this topic.
The prefrontal cortex
The prefrontal cortex is located right behind the forehead. It is influential in governing social interaction and regulation of behaviour. The ability to delay gratification of an impulse is associated with this area. The prefrontal cortex has connections to the amygdala and to the hypothalamus.
Damage to the prefrontal cortex often leads to problems with:
- Anger management
- Irritability
- Impulse control
This explains why Phineas Gage's personality changed so dramatically after his accident.
The anterior cingulate cortex surrounds the frontal part of the corpus callosum (the tissues that connect the two hemispheres of the brain) and connects to the prefrontal cortex and amygdala. It has several functions, including those governing autonomic behaviours, but has been implicated in cognitive functions such as reward anticipation, impulse control and empathy. Damage to or reduced functioning of these prefrontal regions appears to be genuinely linked to increased aggressive behaviour.
Evaluation
Strengths of animal research
Much work investigating aggression and the brain has required the use of specially bred animals for laboratory research. The use of animals in psychological investigations allows for scientific rigour to be applied.
Advantages of Animal Research
More control is possible as animals can be:
- Genetically bred for a specific study
- Housed in carefully monitored environments
- Studied without ethical constraints that apply to human research
This removes the chance of extraneous variables affecting the outcome of the study, making studies using animals extremely well controlled and enabling objective data gathering. This level of control leads to clear cause and effect conclusions being drawn, which would not be possible with human participants because of ethical considerations.
Limitations of animal research
Several problems exist with using animal studies to understand human aggression:
Generalisation across species
There are always problems of generalisability across species. Much of the experimental work investigating the role of brain structure by selectively damaging precise brain areas has been carried out on cats and rodents, although human brains are considerably more complex than those of small mammals. However, some researchers argue that the basics are the same between species and therefore these experiments are worthwhile.
Ethical concerns: There are ethical considerations in the use of animals in research into human psychology. Some argue that such research is immoral as animals are harmed by these types of studies, for example through having parts of their brain lesioned. Others contend that using animals for human benefit in this way is no different from using them for meat or keeping them as pets.
Ethical guidelines now require that all studies using animals require a cost-benefit analysis, which clearly shows that any suffering caused to the animal is outweighed by the potential benefit to humanity.
Support from human case studies
There is support for the link between brain structure and aggression from human case studies such as that of Phineas Gage. Blair, Colledge and Mitchell (2001) found that many patients with psychopathic behaviour patterns have very similar neurocognitive functioning to patients who have suffered damage to the amygdala.
Furthermore, case studies support the findings, suggesting that the prefrontal cortex is genuinely linked to aggression. In a more scientific study of 41 convicted murderers, Raine et al. (1997) found lower activity in the prefrontal cortex and differences in the functioning of the limbic system in brain scans of impulsive murderers.
Raine's Research on Reoffending
Additional research by Raine on prisoners in New Mexico supports the structural explanation. Brain-imaging studies completed before release revealed reliable predictors for reoffending:
- Reduced function in the anterior cingulate
- Smaller amygdala
This provides more robust scientific evidence linking specific brain structures to aggressive behaviour.
Reductionism concerns
The Reductionism Problem
It could be argued that brain functioning as an explanation for aggression is reductionist. It reduces the production of aggressive behaviour and all that this entails down to the working of specific neural circuits and ignores other possible causes such as social learning.
Evidence exists showing that different cultures display much higher than average aggression levels whilst other cultures show much lower levels. This is unlikely to be due to differences in brain structure but more probably caused by social learning and cultural factors.
The link between brain functioning and aggression is supported by research into human cases such as Phineas Gage, however he represents but a single case study and may not be representative of other humans. Other case studies support the findings though, suggesting that the prefrontal cortex is genuinely linked to aggression.
Biological determinism
The argument that brain structure determines aggressive behaviour is known as biological determinism. This is the view that behaviour is predetermined by biological makeup and that individuals have no real control or choice regarding how they behave. Therefore, people with smaller amygdala and low activity in the prefrontal cortex are destined to be aggressive.
Implications of Biological Determinism
These ideas can be used as a defence for violence, with the argument that aggressive behaviour of some offenders could be genetically determined and a result of their biological makeup, as was the case in Raine's research (Section 3.3, Studies).
Potential problems:
- Could provide an excuse for some people to engage in violence
- Individuals might say their behaviour is beyond their control
- Could limit willingness to engage in treatments such as anger management programmes
- Individuals might believe treatments to be futile in the face of biological factors
- Ignores the effects of environmental factors on behaviour
Consistency with genetic explanations
The idea that there is a biological basis for aggression is consistent with genetic explanations because our genetic blueprint builds our brain structures. Therefore, people with a genetic blueprint for aggression would have brain structures that predispose them towards aggressive responses. This could explain why, on average, males across all cultures tend to be more physically aggressive than females.
Key Points to Remember:
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The brain is divided into two hemispheres, each containing four lobes (frontal, parietal, temporal, occipital) that serve different functions.
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Early evidence from Phineas Gage's case demonstrated that damage to the prefrontal cortex can lead to increased aggression and personality changes.
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Key brain structures associated with aggression include the amygdala (emotion centre), hypothalamus (hormone regulation), periaqueductal grey matter (stress response), and prefrontal cortex (impulse control).
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Animal studies have identified different types of aggression (offensive, defensive, predatory) linked to specific brain regions, though generalising these findings to humans presents challenges.
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Evidence supporting the brain structure explanation comes from both case studies and modern neuroimaging research, though ethical concerns and reductionism remain important considerations when evaluating this approach.