Biopsychology

Draw the diagram for the divisions of the nervous system

Define the human nervous system

The human nervous system is a complex network of nerve cells that carry messages to and from the brain and spinal cord to different parts of the body. 

Explain the central nervous system(CNS)

The central nervous system (CNS) comprises the brain and spinal cord. The brain is divided into separate areas, each which has a different function; these range from controlling thought and speech to controlling skills and balance. The function of the spinal cord is to relay information between the brain and the rest of the body. 

Explain the peripheral nervous system (PNS)

The peripheral nervous system (PNS) comprises the nerves outside the CNS. It relays nerve impulses between the CNS and the rest of the body. The PNS has two main divisions:

• The autonomic nervous system (ANS)

• somatic nervous system (SNS)

Explain the autonomic nervous system (ANS)

The autonomic nervous system (ANS) controls involuntary actions that we have no conscious control over. The ANS connects to internal organs and glands and has two divisions: the sympathetic nervous system, which has an arousing effect on the body, such as preparing the body for ‘Fight or Flight’; and the parasympathetic nervous system, which has a calming effect and helps the body return to homeostasis after a period of excitation. 

Explain the somatic nervous system (SNS)

The somatic nervous system (SNS) consists of sensory neurons which send information from sense organs to the CNS. It also consists of motor neurons which send information from the CNS to voluntarily control skeletal muscles. 

What is a neuron?

A neuron is a cell that carries electrical impulses throughout the body. 

Draw the structure of a typical neuron

What is the function of the dendrite?

Extensions at the beginning of a neuron that increase the surface area of the cell body. They receive information from other neurons and transmit electrical stimulation to the cell body. They are covered with receptors. 

What is the function of the cell body (soma)?

Produces proteins for the dendrites, axons and synaptic terminals, provides energy to trigger an action potential.

What is the function of the nucleus?

Contains the genes, consisting of DNA which contains the cell history and information to manufacture all the proteins characteristic of a nerve cell. 

What is the function of the axon?

The main conducting unit of the neuron, capable of conveying electrical signals along distances that range from as short as 0.1 millimetre (in the brain) to as long as 1 metre (from the spinal cord to big toe). Many axons split into several branches, thereby conveying information to different targets. Many axons are wrapped in protective myelin sheath which are broken at various points by the nodes of Ranvier. 

What is the function of the axon terminal?

Are located on one end of a neuron. It is the final part of a neuron to receive an electrical impulse and is also the area where the impulse is converted to a chemical signal. It transfers information from its neuron into another neuron, though it does not come into physical contact with the other neuron. 

Name the three types of neurons

• sensory

• relay

• motor

Draw the diagram of a sensory neuron

Draw the diagram of a relay neuron

Draw the diagram of a motor neuron

Explain the features and functions of a sensory neuron

Features  Unipolar – cell body has one branch  No dendrites on cell body  Long dendrites connect to axon  Myelin covers axon

Functions  Afferent nerve cell that carries sensory impulses from the sense organs (e.g. skin) to the CNS

Explain the features and functions of a relay neuron

Features  Multipolar – cell body has many branches  Short dendrites  Several dendrites  Short axon  No myelin on axon  Entirely within the CNS

Functions  Enables sensory neurons and motor neurons to communicate

Explain the features and functions of a motor neuron

Features  Multipolar – cell body has many branches  Short dendrites  Several dendrites  Long axon  Myelin covers axon

Functions  Efferent nerve cell that transmits nerve impulses from the CNS to muscles or glands

Draw the diagram for connectivity of types of neurons

What is a synapse?

A synapse is the junction between the axon of one neuron and the dendrites of another

What are the structures in the synaptic transmission?

The main features of the synapse include the vesicles in the axon terminal of the pre-synaptic neuron, which are sacs filled with neurotransmitters (chemical messengers). 

The synaptic gap (sometimes called space or cleft) is the tiny gap between the two neurons. 

The receptors on the dendrites of the post-synaptic neuron receive the neurotransmitters. 

Draw the diagram for the structures in synaptic transmission

What is the Synaptic transmission?

the process by which one neuron communicates with another.

Draw the diagram for the processes in synaptic transmission

Explain the process of synaptic transmission

1. Information is passed down the axon of the pre-synaptic neuron as an electrical impulse known as an action potential.  

2. The action potential reaches the axon terminal and triggers release of neurotransmitters from vesicles. 

3. Neurotransmitters diffuse across the synaptic gap to carry the chemical signal from the presynaptic neuron to the post-synaptic neuron.  

4. Neurotransmitters bind to receptor sites on the post-synaptic neuron. 

5. Stimulation of post-synaptic receptors can result in excitation or inhibition of the post-synaptic membrane

Information travels in one direction at the synapse 

• Vesicles containing neurotransmitters are only present in the pre-synaptic membrane. 

• Receptors for neurotransmitters are only present on the post-synaptic membrane. 

• During diffusion, neurotransmitters travel from levels of high concentration at the pre-synaptic membrane to levels of low concentration at the post-synaptic membrane. 

Once neurotransmitters bind to a receptor on the post-synaptic neuron, they have an excitatory or inhibitory effect. This determines whether an action potential (electrical impulse) is fired from the neuron’s cell body, which then travels along its axon. 

Describe Excitation and give an example of a neurotransmitter

Description:

• Increases neural activation in the postsynaptic neuron (creates an excitatory post-synaptic potential). 

• Makes the post-synaptic neuron more likely to fire. 

• Increases the activity of other neurotransmitters. 

Neurotransmitter Example:

• Glutamate 

  • Necessary for cognition, memory and learning. 

  • High levels can over-excite neurons until they die, causing brain disorders such as Alzheimer’s disease. 

Describe Inhibition and give an example of a Neurotransmitter

Description:

• Decreases neural activation in the postsynaptic neuron (creates an inhibitory post-synaptic potential). 

• Makes the post-synaptic neuron less likely to fire. 

• Decreases the activity of other neurotransmitters. 

• Balances periods of excitation. 

Neurotransmitter Example:

• GABA 

• Regulates cortical functions, e.g. motor control. 

• Low levels can lead neurons firing too often and too easily and has been linked to anxiety and epilepsy. 

Explain summation

The firing of an action potential in the post-synaptic neuron depends on the summation (combination) of all the excitatory post-synaptic potentials and inhibitory post-synaptic potentials. If there is more excitation than inhibition a new action potential is created in the postsynaptic neuron. If there is more inhibition than excitation a new action potential is not created. 

Draw the diagram for summation

What is a hormone?

A hormone is a chemical messenger that circulates in the blood and regulates bodily processes that influence behaviour or mood. 

What is the function of the endocrine system?

• Regulate the activity of cells and organs in the body to maintain homeostasis and promote appropriate growth, metabolism and reproduction. 

• Communicate chemical messages by secreting hormones from glands which travel through the bloodstream to specific organs and tissues. 

Explain the pituitary gland

The pituitary gland is often considered the ‘master gland’ of the endocrine system because it produces hormones that control many functions of other endocrine glands. 

For example, Luteinising hormone (LH) travels from the pituitary gland through the bloodstream to the testes, which in turn produce testosterone, which acts locally to support sperm production and in high levels has been linked to higher levels of aggression

Explain the pineal gland

The main function of the pineal gland is to produce the hormone melatonin. In humans, melatonin production is stimulated by darkness and is used to initiate and maintain sleep as part of the sleep-wake cycle. 

Explain the adrenal glands

Each section of the adrenal glands secretes a variety of different hormones. For example, the adrenal medulla releases the hormone adrenaline which is involved in the body’s fight or flight response to stress.  

Explain the differences between Neurotransmitters and Hormones

• Neurotransmitters are produced within neurons and pass very quickly from one neuron, across the synaptic cleft, to another nearby neuron… whereas… 

• Hormones are secreted by glands and travel less quickly through the bloodstream to often quite distant target organs. 

Explain the fight or flight response

The fight or flight response is generated during threatening situations. It involves the activation of the sympathetic branch of the autonomic nervous system which causes immediate physiological changes that enable us to respond appropriately. 

Explain the process of a sympathetic response

1. A stressor is perceived and the threat is assessed. 

2. The hypothalamus activates the sympathetic branch of the autonomic nervous system (ANS).   

3. Sympathetic nerves transmit the signal from the central nervous system (CNS) to the Peripheral nervous system (PNS), which consists of nerves which connect to the adrenal glands. 

4. The adrenal medulla (the inner part of the adrenal glands) releases the hormones adrenalin and noradrenaline into the bloodstream. 

5. Adrenaline constricts blood vessels in the skin to divert blood to the muscles to provide oxygen so they can provide a physical response to threat. 

What is the role of adrenaline?

• Adrenaline is a hormone released as part of the ‘fight or flight response’ which prepares the body for action in different ways: 

• Increase heart rate – to speed up blood flow. 

• Increase blood pressure – to speed up force of blood flow. 

• Increase lung function – to provide oxygen to the muscles and brain. 

• Increase blood glucose – to provide energy. 

• Increase blood flow to muscles – to increase physical mobility. 

• Increase pupil size (dilation) – to let in more light to improve perception of a stressor. 

• Decrease digestion – as blood is directed to muscles (causing ‘butterflies in stomach’). 

• Decrease salivation – as digestion is not prioritised. 

Explain the Parasympathetic Response 

Once the stressor has gone, the autonomic nervous system switches from the activation of the sympathetic branch to the parasympathetic branch. This leads to a decrease in the hormones, such as adrenaline, in the bloodstream. This opposing, calming effect on the body is known as the ‘rest and digest response’ and includes a decrease in heart rate and the return of digestive processes. Ultimately, parasympathetic activation returns the body to a balanced state known as homeostasis. 

What are the strengths and limitations to the flight or fight response?

Strengths:

• Research into the fight or flight response is scientific

Limitations:

• The fight or flight response may apply to males more than females

• Fight or flight may not be the first reaction to a threat

• The fight or flight response may have negative consequences

Evaluate ‘research into the fight or flight response is scientific’ as a strength of the fight or flight response

An advantage of research into the fight or flight response is the ability to scientifically investigate physical reactions. Experimental methods can be used which involve participants being presented with stimuli of varying degrees of threat under controlled conditions. The subsequent biological responses can be objectively monitored using equipment such an ECG which measures heart rate. Researchers do not need to use self-report methods to assess a participant’s bodily response which is less subject to bias. This suggests that the research into the fight or flight response has validity. 

Evaluate ‘The fight or flight response may apply to males more than females’ as a limitation of the fight or flight response

When males are confronted by stressful situations a fight or flight response may commonly be triggered; females may be more likely to adopt a ‘tend and befriend’ response. ‘Tend’ refers to protective behaviours and ‘befriend’ refers to the formation of social alliances to cope with the stressor. Assuming females adopt a fight or flight response to threat would be an example of beta bias as gender differences in responses to threat are minimised. 

Evaluate ‘fight or flight may not be the first reaction to a threat’ as a limitation of the fight or flight response

It is overly simplistic to assume that fight and flight is the initial response to a threat. It has been suggested that most animals initially adopt a ‘freeze’ response in order be more alert to any signs of danger. This enables the animal to focus its attention and more effectively assess the most appropriate response to a particular threat. Although the animal may then proceed to fight or flee from the threat, this is only as part of a more elaborate process. 

Evaluate ‘the fight or flight response may have negative consequences’ as a limitation of the fight or flight response

Despite helping early humans to survive in dangerous situations, the fight or flight response may no longer be adaptive and actually have numerous disadvantages. Stressors present in modern life such as consistent workplace stress do not require the instant physical reaction afforded by the fight or flight response. As a consequence, continued physiological strain is placed on the body such as increased blood pressure, which can lead to the damage of blood vessels and eventually heart disease. This suggests that the fight or flight response may be an evolutionary hangover and actually detrimental to many modern humans as the way of living has changed. 

Explain how Functional Magnetic Resonance Imaging (fMRI) is used as a way of studying the brain

• Indirectly measures electrical activity of neurons by recording changes in brain blood flow while a person completes a cognitive task. 

• As a particular area of the brain becomes more active, it requires more oxygen, which is supplied via bloodstream. 

• As the blood becomes deoxygenated its magnetic properties change. 

• The difference in magnetic properties is detected by applying radio waves to the brain which is converted into a computer image. 

• A stable radio wave signal indicates more blood flow and therefore high neural activity: these active areas appear as bright colours to give a moving image of the brain. 

What is the strength and limitation of fMRI?

Strength:

• high spatial resolution

Limitation:

• difficulty of interpreting the data

Evaluate ‘high spatial resolution’ as a strength of fMRI

strength of fMRI is its high spatial resolution which means the activity of the brain is precisely measured to an accuracy of 1-2 millimetres. This is important when identifying small areas with specific functions such as Broca’s area involved in speech production. It also allows for deep areas of the brain to be investigated, which is useful in memory research focusing on subcortical areas such as the hippocampus. This ultimately means fMRI can measure how brain activity is localised, which is an advantage over an EEG which measures more general activity in superficial cortical areas. 

Evaluate ‘difficulty interpreting the data’ as a limitation of fMRI

A limitation of fMRI scans is the difficulty of interpreting the data. Completing a specific cognitive task during an fMRI scan will often simultaneously activate many different areas in the brain. It is therefore challenging to infer cause and effect between the exact involvement of a particular brain region and the function being investigated. Some psychologists also argue that although localised activity is revealed by an fMRI scan, this cannot reveal details about the communication between different brain areas, which therefore fails to provide a holistic understanding of neural functioning. 

Explain how Electroencephalogram (EEG) is used as a way of studying the brain

• Electrodes are placed on the scalp. 

• The electrodes directly measure electrical activity of neurons on the surface of the brain. 

• They continually measure neural activity during brain states such as sleep and arousal. 

• Electrical signals from different electrodes are recorded over an extended period of time to produce an EEG graph. 

What are the strengths and limitations of the EEG?

Strength:

• they have led to developments in our understanding of regular brain functions

Limitations:

• practical issue associated with using the equipment

Evaluate ‘they have led to developments in our understanding of regular brain functioning’ as a strength of EEG

A strength of an EEG is that they have led to developments in our understanding of regular brain functions and the diagnosis of conditions such as epilepsy and Alzheimer’s. For example, EEG scans have allowed us to gain deeper understanding into the stages of sleep. Dement and Kleitman studied 9 participants who slept for up to 61 nights in a laboratory whilst their brain activity was recorded using an EEG. They found that brain activity changed in sleep cycles throughout an entire sleep period. The participant awakened during REM sleep reported dreams 80-90% of the time, compared to only 7% for NREM sleep. This is a strength as the use of EEG scans has allowed for strong empirical evidence for the five stages of sleep occurring as part of an ultradian rhythm.  

Evaluate ‘practical issue associated with using the equipment’ as a limitation of EEG

A limitation of an EEG is the practical issue associated with using the equipment. Attaching electrodes to the scalp directly or via a skull cap can be uncomfortable for the participant, which could result in the measurement of brain activity that does not occur whilst a participant is not using the equipment in an everyday environment. The level of discomfort and lack of representativeness is exacerbated by the fact that EEGs are often used to measure general brain states over a period of hours in a clinical setting. This may put off many participants from taking part in typical research using EEGs and therefore limit population validity because only those willing to undergo such procedures will volunteer. 

Explain how Event-Related Potentials (ERPs) are used as a way of studying the brain

• Electrodes are placed on the scalp. 

• The electrodes directly measure electrical activity of neurons on the surface of the brain. 

• ERPs are very small changes in electrical activity of the brain triggered by specific stimuli presented to the participant (e.g. a sound or flashing light). 

• Many EEG readings are taken whilst the same stimulus is presented and an average reading is calculated. 

• A consistent neural response to the stimulus will appear as a clear ERP. Any inconsistent, extraneous background neural activity (‘noise’) will be filtered out. 

What are the strengths and limitations of using ERPs?

Strength:

• high temporal resolution

Limitation:

• low spatial resolution

Evaluate ‘their high temporal validity’ as a strength of ERPs

A strength of using ERPs is their high temporal resolution, which refers to how quickly the scanner can detect changes in brain activity. Neural activity in the brain corresponds to an ERP graph with only a 1-millisecond delay, which is advantageous compared to fMRI that has a delay of 1-4 seconds. Since an ERP directly measures neural activity, it can investigate the brain where timing is important. Researchers have identified many types of ERP and described the precise roles of these in such as in the measurement of cognitive functions and deficits. An example of this is an ERP which is thought to be involved in the allocation of attentional resources in working memory. This shows that it is possible to identify brain activity whilst completing specific cognitive tasks. 

Evaluate ‘low spatial resolution’ as a limitation of ERPs

A limitation of using ERPs is low spatial resolution. Whilst the ERP measures brain activity in response to a specific event, it is unable to identify the specific location of where the brain activity is. This is because each electrode measures the general activity of many thousands of neurons and can only detect the activity in superficial cortical regions of the brain and not deeper areas. This is unlike fMRI where psychologists can determine the activity of different brain regions with greater accuracy. This suggests that ERP is not an ideal choice when psychologists are trying to pinpoint specific brain regions performing specific functions. 

Explain Post-Mortem Examinations

• Involves the analysis of a person’s brain after their death. 

• If a person had a rare disorder or displayed abnormal behaviour during their lifetime, a post-mortem may establish the neurobiological cause. 

• Comparisons to neuro-typical brains may also be used to ascertain the extent of the differences. 

• A famous post-mortem was carried out on Louis Leborgne. This revealed extensive damage to his Broca’s area, which was linked to his inability to produce speech except for the nonsense word “tan”. 

What is the strength and limitation of Post-Mortem Examinations?

Strength:

• they facilitate investigation of deeper areas of the brain

Limitation:

• post-mortem delay

Evaluate ‘they facilitate investigation of deeper areas of the brain’ as a strength of post mortem examinations

A strength of post-mortem examinations is they facilitate investigation of deeper areas of the brain which EEGs and ERPs cannot reveal. Historically, they have provided vital evidence to help reveal and verify structural areas of the brain that are responsible for neural processing. For example, it was only after Louis Leborgne’s death that Paul Broca was able to conduct the post-mortem examination which revealed damage to Broca’s area. This subsequently triggered further research into this as an area localised for speech production. 

Evaluate ‘post mortem delays’ as a limitation of post mortem examinations

One limitation using post-mortem examinations is the post-mortem delay between death and examination which can be up to 3 days. During this time interval, changes to the neuroanatomy of the brain may occur, which means that the findings at the time of the examination may not have been present whilst the person was alive. A related problem involves the issue of causation. Any functional deficits experienced by the person may not have been due to the damage revealed in the post-mortem examination, but to some unrelated trauma or decay. For example, in Louis Leborgne’s case, his speech production deficits and Broca’s area damage may have had a co-incidental rather than causational link. 

Evaluation of Ways of Studying the Brain 

Technique	Scan/  Non-scan	Spatial resolution	Temporal resolution	Invasive/  Non-invasive	Neural measure	Depth of analysis
fMRI	Scan	High	Low	Non-invasive	Indirect	Deep
EEG	Scan	Low	High	Non-invasive	Direct	Superficial
ERPs	Scan	Low	High	Non-invasive	Direct	Superficial
Post-mortem	Non-scan	N/A	N/A	Invasive	N/A	Deep

Define localisation of function

Localisation of function refers to the principle that specific areas of the brain have specific functions. 

Explain the cerebral cortex

The internal areas of the brain are covered by a 3mm outer layer called the cerebral cortex which is divided up and named according to its function. 

Draw the diagram for -

Area of the Brain	Location	Function	Hemisphere	Effects of Damage
MOTOR CORTEX	Frontal lobe	Controls voluntary movements by sending signals to the muscles in the body.	Both: The motor cortex of each hemisphere controls the muscles on the opposite side of the body.
SOMATOSENSORY CORTEX	Parietal Lobe	Receives incoming sensory information from the skin to produce sensations related to pressure, pain, temperature, etc.	Both: The somatosensory cortex of each hemisphere receives information from the opposite side of the body.
VISUAL CORTEX	Occipital Lobe	Receives and processes visual information. Contains different parts that process different types of information including colour shape and movement.	Both: Information from the right visual field is processed in the visual cortex of the left hemisphere. Information from the left visual field is processed in the in the visual cortex of right hemisphere.
AUDITORY CORTEX	Temporal Lobe	Receives and processes acoustic information. Enables auditory stimuli to be identified and spatially located.	Both: Information from the left ear goes primarily to the right hemisphere and information from the right ear goes primarily to the left hemisphere.
BROCA’S AREA	Left Frontal Lobe	Responsible for speech production. Damage leads to production aphasia, which involves difficulties formulating speech.	Lateralised to the left.	Broca’s aphasia- non-fluent speech: short sentences, miss out words (can also affect writing)
WERNICKE’S AREA	Left Temporal Lobe	Responsible for the interpretation of speech. Damage leads to receptive aphasia, which involves difficulties understanding speech.	Lateralised to the left.	Wernicke’s aphasia - poor language comprehension, speech appears fluent but may be jumbled or lack context

What are the strengths and limitations of Research into Localisation of Function in the Brain?

Strengths:

• Evidence supporting localised brain functions

• A methodological strength of research into localisation of function

Limitations:

• Evidence refuting localised brain functions

• Beta bias in research into localisation of function

Evaluate ‘Evidence supporting localised brain functions’ as a strength of Research into Localisation of Function in the Brain

Evidence supporting localised brain functions is provided by Broca (1865). He conducted a case study on Louis Leborgne, who was often referred to as ‘Tan’ because that was the only syllable that he could say despite being able to understand spoken language. A post-mortem examination found damage to an area of the left frontal lobe. This supports the localisation of a ‘language centre’ specialised for speech production which is known now as ‘Broca’s area’. In the case study of Phineas Gage (1848) an accidental explosion during railroad construction shot a metal pole into his left cheek and through the top of his head damaging a significant part of his frontal lobe. As a result, Gage suffered drastic changes to his personality from someone who was calm to someone who was quick-tempered and rude. This supports the localisation of emotional control to the pre-frontal cortex of the frontal lobe

Evaluate ‘A methodological strength of research into localisation of function’ as a strength of Research into Localisation of Function in the Brain

A methodological strength of research into localisation of function is the use of objective ways of studying the brain. For example, post-mortems allow damaged structures of the brain to be identified in an unbiased way, which can be linked to the corresponding functions that affected a person when they were alive. Additionally, modern brain scans, such as fMRI allow the activity of the brain to studied in an impartial way whilst a person completes a task, which enables specific functions a person is performing to be localised to a specific brain area.

Evaluate ‘Evidence refuting localised brain functiona’ as a limitation of Research into Localisation of Function in the Brain

Evidence refuting localised brain functions is provided by Lashley (1950). He removed 10-50% of the cortex in rats that were learning a maze. He found that regardless of the area removed, rats could recover and relearn how to complete the task. This suggests areas of the cortex have equipotentiality – the ability of intact parts of the brain to perform functions lost by the destruction of other parts. Higher cognitive functions (e.g. those involved with learning) may therefore not be localised but distributed holistically throughout the brain.

Evaluate ‘Beta bias in research into localisation of function’ as a limitation of Research into Localisation of Function in the Brain

Beta bias in research into localisation of function. Some psychologists argue that the idea of localisation of function fails to account for gender differences. Herasty (1997) found that women have proportionally larger Broca’s and Wernicke’s areas than men which can perhaps explain the greater ease of language use amongst women. This suggests a level of beta bias in the theory: the differences between men and women are ignored and variations in the size and activation of the areas used during various language activities are not considered. Therefore, caution should be made when generalising research findings into localisation of function between males and females equally as different brain structures/size.

Explain the idea of Hemispheric lateralisation

Hemispheric lateralisation is the idea that the two halves (hemispheres) of the brain are functionally different, with certain mental processes being mainly controlled by one hemisphere rather than the other (e.g. language lateralised to the left hemisphere). The two hemispheres are connected by the corpus callosum, which is a bundle of nerve fibres that allows the two areas to communicate.

Explain Split-brain research

Split-brain research typically involves epileptic patients who have had their hemispheres surgically separated by cutting their corpus callosum, which is in order to reduce the severity of their epileptic seizures. This allows researchers to investigate the extent to which brain functions are lateralised.

What did Sperry conduct research on?

Since the first split-brain study in 1967, Sperry conducted numerous variations of studies into hemispheric lateralisation. 

Evaluate the example procedure of Sperry’s Research

Example procedure: A participant sits close to a screen and fixates on a dot. A different word is simultaneously presented to the left and right of the dot for 1/10 second so there is no time for the participant to move their eyes to view both words. There is a selection of objects relating to the words behind the screen. Participants are then asked to: 

• Say the words they see on the screen. 

• Pick up objects with their left hand which represents what they see. 

Evaluate the example findings of Sperry’s Research

Example findings: When the word ‘key’ was presented to the left visual field simultaneously with the word ‘ring’ to the right visual field, participants: 

• Said “ring”. 

• Picked up the key with their left hand. 

Evaluate the conclusions of Sperry’s research

Both hemispheres are responding independently and are not able to integrate the information because of the severed corpus callosum. 

Participants say “ring” because the image of the word in their right visual field passes to the visual cortex of the left hemisphere of the brain. The left hemisphere contains language centres so the person is able to vocally produce the word ‘ring’. 

Participants only pick up the key because the image of the word in their left visual field passes to the visual cortex of the right hemisphere of the brain. This hemisphere contains spatial processing abilities and the right motor cortex, which controls muscles on the left side of the body, which enables the left hand to pick up the object relating to word ‘key’. 

Overall, split-brain research suggests that there is hemispheric lateralisation in the brain: language is lateralised to the left hemisphere and visual-spatial processing is lateralised to the right hemisphere. 

What are the strengths and limitations of Research into Hemispheric Lateralisation?

Strengths:

• A strength of split-brain studies is the use of scientific methodology.

• Hemispheric lateralisation research has implications for how we understand consciousness.

Limitations:

• A limitation of split-brain research is the use of small sample sizes.

• Contradictory findings for idea that language is lateralised to the left hemisphere

Evaluate ‘A strength of split-brain studies is the use of scientific methodology’ as a strength of research into Hemispheric Lateralisation

Split-brain studies usually find that each hemisphere of the brain is functionally distinct which suggests that two minds exist within one person. Other theorists believe that such conclusions over-emphasise the differences between the hemispheres and that we have one mind which involves an integrated system that uses both hemispheres in most everyday tasks. 

Evaluate ‘Evaluation of Research into Hemispheric Lateralisation 

A limitation of split-brain research is the use of small sample sizes’ as a limitation of Research into Hemispheric Lateralisation

Because the numbers of people with severe epilepsy who have had their corpus callosum cut are small, the generalisability of the findings is limited. It could be that epilepsy causes unique changes in the way the brain functions, which is not typical of other people. Also, there were differences in the extent of the disconnection between the two hemispheres within the epileptic sample. These factors decrease the population validity of the research. 

Evaluate ‘Contradictory findings for idea that language is lateralised to the left hemisphere’ as a limitation of research into hemispheric lateralisation

are provided by Turk et al. (2002). They conducted a case study on a patient known as J.W., who developed the capacity to speak using his right hemisphere regardless of whether information was presented to his left or right visual field. This supports the idea of brain plasticity – different areas of the brain are equipotential which means neural connections can be reorganised in order to maintain certain functions after brain damage has occurred. This goes against the findings that support the role of hemispheric lateralisation. 

Define plasticity

Plasticity is the ability of the brain to change and adapt functionally and physically in response to experience. 

Explain the plasticity of the brain

During infancy, the brain experiences rapid growth in the number of neurons and synaptic connections; by the age of 2-3 an infant brain has more neurons and connections than in a mature adult brain. This decline can be explained by the process of synaptic pruning, where frequently used connections are strengthened and rarely used connections are weakened. 

It was originally thought that brain plasticity was not present in adulthood after the brain reached the critical period of maturity at age 20. However, recent research suggests that although plasticity is less evident in the later life, new neural connections can be formed as a result of learning and experience. This can be explained by different functional demands at different ages. In infancy, the range of new experiences means the brain has to adapt drastically, whereas in adulthood there may be more specific demands requiring only certain areas of the brain to adapt.

Explain functional recovery

Functional recovery is a form of plasticity whereby, following damage to the brain through trauma, the brain is able to regain some or all of the functions that were initially impaired. 

What are the common types of brain trauma?

Common types of brain trauma include:

• physical trauma,

• cerebral haemorrhage,

• cerebral ischaemia (e.g. stroke) and infections.

• Such trauma can result in a physical loss of brain tissue or a loss of functionality within the affected area. 

What happens in response to the damage?

In response to the damage caused by trauma, other undamaged areas of the brain may compensate in different ways: 

• Neural reorganisation involves a different area of the brain adopting the functions of the damaged area. For example, if Broca’s area is damaged in the left hemisphere, the right hemisphere equivalent area may adopt its functions. 

• Axonal sprouting involves the growth of new nerve endings from surviving neurons which then connect to areas of the brain the damaged neurons used to connect to. 

• Neural regeneration involves the growth of completely new neurons. 

• Reformation of blood vessels may result if cerebral haemorrhage or cerebral ischaemia has damaged the blood supply to the affected areas

What are the strengths and limitations of Research into Plasticity and Recovery of the Brain?

Strengths:

• Evidence to support the idea of plasticity

• A strength of understanding about brain plasticity in recovery is the practical application

• The idea of plasticity and functional recovery of the brain can account for nurture factors that shape brain development

Limitations:

• Plasticity can have negative implications for individuals

Evaluate ‘Evidence to support the idea of plasticity’ as a strength of Research into Plasticity and Recovery of the Brain

Evidence to support the idea of plasticity comes from Maguire et al. (2000) who studied spatial navigation abilities in London taxi drivers. Using an MRI scanner, they calculated the amount of grey matter (neuron cell bodies) in the brains of taxi drivers and a control group. They found that the posterior hippocampi of taxi drivers were significantly larger relative to the control group and that volume was positively correlated to the amount of time they had been taxi drivers. This suggests the part of the brain responsible for memorising spatial information had physically adapted to cope with the cognitive demands of the job. 

Evidence that suggests plasticity and recovery differs with age is provided by Teuber (1975) who studied soldiers with brain damage which affected movement and vision. He found 60% of those under 20 showed significant improvement, whilst only 20% of those over 26 showed similar recovery. This suggests that neural reorganisation and axonal sprouting and may be more extensive in younger brains, but also that brain plasticity is still possible in adulthood. 

Evaluate ‘A strength of understanding about brain plasticity in recovery is the practical application’ as a strength of research into Plasticity and Recovery of the Brain

A strength of understanding about brain plasticity in recovery is the practical application of this knowledge in the field of neuro-rehabilitation. Although the brain can recover itself to a certain extent after trauma, this slows down after several weeks. Understanding the role of plasticity in recovery has led to therapeutic techniques that can assist this process. For example, following a stroke, movement therapy and electrical stimulation of the brain can help restore motor and cognitive deficits. Such applications, based on the idea of plasticity can improve the chances that an individual can functionally recover. 

Evaluate ‘The idea of plasticity and functional recovery of the brain can account for nurture factors that shape brain development’ as a strength of Research into Plasticity and Recovery of the Brain

Rather than accepting the deterministic view that physical and cognitive abilities controlled by the brain are fixed by genes at an early age, the wealth of research shows that interaction with the environment can influence how our brains develop. Although there are limitations to our capabilities, we have a degree of control over the life experiences we encounter, which ultimately suggests we have the free will to decide how we develop. Such insight provides a positive outlook on our lives, especially for those suffering from trauma. 

Evaluate ‘Plasticity can have negative implications for individuals’ as a limitation of Research into Plasticity and Recovery of the Brain

For example, prolonged drug use can lead the brain to re-wire itself resulting in poorer cognitive functioning as well as an increased risk of dementia later in life (Medina et al. 2007). Also 60-80% of amputees have been known to develop phantom limb syndrome – the continued experience of sensations in the missing limb as if it were still there. These sensations are usually unpleasant, painful and are thought to be due to neural reorganisation in the somatosensory cortex that occurs as a result of limb loss (Ramachandran & Hirstein 1998). This highlights the impact that negative environmental influences (nurture) can have upon the brain (nature).