The Brain

Question 1

Localisation of Function

Answer 1

Localisation of function is the idea that certain functions (e.g., language and memory) have certain locations within the brain.

Question 2

Evidence for Localisation of Function

Answer 2

• One such case study is that of Phineas Gage.
• In 1848, while working on a rail line, he experienced a drastic accident in which an iron rod went through his skull.
• Although Gage survived this ordeal, he did experience a change in personality, such as loss of inhibition and anger.
• This change provided evidence to support the theory of localisation of brain function, as it was believed that the area the iron stake damaged was responsible for personality.
• The four areas you need to be aware of are:
  1. Motor area
  2. Somatosensory area
  3. Visual area
  4. Auditory area

Question 3

Motor Area

Answer 3

Theory:
- Motor area located in the frontal lobe.
- Responsible for voluntary movements by sending signals to the muscles in the body.

Study:
- Hitzig and Fritsch first discovered that different muscles are coordinated by different areas of the motor cortex by electrically stimulating the motor area of dogs.
- This resulted in muscular contractions in different areas of the body depending on where the probe was inserted.
- The regions of the motor area are arranged in a logical order, for example, the region that controls finger movement is located next to the region that controls the hand and arm and so on.

Question 4

Somatosensory Area

Answer 4

Theory:
- Somatosensory area located in the parietal lobe.
- Receives incoming sensory information from the skin to produce sensations related to pressure, pain, temperature, etc.
- Different parts of the somatosensory area receive messages from different locations of the body.

Study:
- Robertson found that this area of the brain is highly adaptable, with Braille readers having larger areas in the somatosensory area for their fingertips compared to normal sighted participants.

Question 5

Visual Area

Answer 5

Theory:
- Visual area located in the occipital lobe.
- Receives and processes visual information.
- Information from the right visual field is processed in the left hemisphere, and information from the left visual field is processed in the right hemisphere - contralateral
- The visual area contains different parts that process different types of information, including colour, shape or movement.

Question 6

Auditory Area

Answer 6

Theory:
- Auditory area located in the temporal lobe.
- Analyses and processes acoustic information.
- Information from the left ear goes primarily to the right hemisphere and information from the right ear goes primarily to the left hemisphere.
- The auditory area contains different parts, and the primary auditory area is involved in processing simple features of sound, including volume, tempo and pitch.

Question 7

Language Centres: Broca’s Area

Answer 7

• Broca’s area named after Paul Broca, who discovered this region while treating a patient named Leborgne, who was more commonly referred to as ‘Tan’.
• Tan could understand spoken language but was unable to produce any coherent words, and could only say ‘Tan’.
• After Tan’s death, Broca conducted a post-mortem examination on Tan’s brain and discovered that he had a lesion in the left frontal love.
• This led Broca to conclude that this area was responsible for speech production.
• People with damage to this area experience Broca’s aphasia, which results in slow and inarticulate speech.

Question 8

Language Centres: Wernicke’s Area

Answer 8

• Carl Wernicke discovered another area of the brain that was involved in understanding language.
• Wernicke found that patients with lesions to Wernicke’s area were still able to speak, but unable to comprehend language.
• Wernicke’s area is found in the left temporal lobe, and is thought to be involved in language processing/comprehension.
• People with damage to this area struggle to comprehend language, often producing sentences that are fluent but meaningless - Wernicke’s aphasia.
• Wernicke concluded that language involves a separate motor and sensory region. The motor region is located in Broca’s area and the sensory region is located in Wernicke’s area.

Question 9

Evaluating Localisation of Function - Strength

Answer 9

Point: There is a wealth of case studies on patients with damage to Broca’s and Wernicke’s areas that have demonstrated their functions.

Explanation: For example, Broca’s aphasia is an impaired ability to produce language; in most cases, this is caused by brain damage in Broca’s area. Wernicke’s aphasia is an impairment of language perception, demonstrating the important role played by this brain region in the comprehension of language.

Evidence: (Refer to Tan)
- Post mortem
- Limited in its application to a living brain

Justification: This suggests that functions are localised to specific regions of the brain as portrayed through the existence of language centres.

Question 10

Evaluating Localisation of Function - Weakness

Answer 10

Point: However, although there is evidence from case studies to support the function of the Broca’s area and Wernicke’s area, more recent research has provided contradictory evidence.

Evidence: Dronkers et al. conducted an MRI scan on Tan’s brain to try to confirm Broca’s findings. Although there was a lesion found in Broca’s area, they also found evidence to suggest other areas may have contributed to the failure in speech production.

Justification: These results suggest that the Broca’s area may not be the only region responsible for speech production and the deficits found in patients with Broca’s aphasia could be the result of damage to other neighbouring regions.

Implication: This implies that perhaps Broca’s area is not responsible for speech production, hence reducing the validity of theory of localisation of brain function.

Question 11

Evaluating Localisation of Function - Weakness

Answer 11

Point: Psychologists suggest that it is more important to investigate how the brain areas communicate with each other, rather than focusing on specific brain regions.

Evidence: Wernicke claimed that although the different areas of the brain are independent, they must interact with each other in order to function. An example to demonstrate this is a man who lost his ability to read, following damage to the connection between the visual cortex and the Wernicke’s area, which was reported by Dejerine.

Justification: This suggests that interactions between different areas produce complex behaviours such as language. Therefore, damage to the connection between any two points can result in impairments that resemble damage to the localised brain region associated with that specific function.

Implication: This reduces the credibility of the localisation theory.

Question 12

Evaluating Localisation of Function - Weakness

Answer 12

Point: Critics argue that theories of localisation are biologically reductionist in nature.

Explanation: It is believed that this theory aims to reduce very complex human behaviours and cognitive processes to one specific brain region.

Evidence: For example, the production and comprehension of language has been localised to language centres known as Broca’s area and Wernicke’s area. Such critics suggest that a more thorough understanding of the brain is required to truly understand complex cognitive processes like language.

Justification: This suggests that the theory of localisation of brain function is limited in its explanation as it simplifies complex human behaviours and functions into a set of localised regions of the brain.

Question 13

Evaluating Localisation of Function - Weakness

Answer 13

Point: Some psychologists argue that the idea of localisation fails to take into account individual differences.

Evidence: Herasty found that women have proportionally larger Broca’s and Wernicke’s area than men, which can perhaps explain the greater ease of language use amongst women.

Justification: This suggests a level of beta bias in the theory: the differences between men and women are ignored, and variations in the pattern of activation and the size of areas observed during various language activities are not considered.

Question 14

Evaluating Localisation of Function - Weakness

Answer 14

Point: The claim that functions are localised to certain areas of the brain has been criticised.

Evidence: Lashley proposed the equipotentiality theory, which suggests that the basic motor and sensory functions are localised, but that higher mental functions are not. He claimed that intact areas of the cortex could take over responsibility for specific cognitive functions following brain injury.

Justification: This therefore casts doubt on theories about the localisation of function, suggesting that functions are not localised to just one region, as other regions can take over specific functions following brain injury.

(Plasticity/Functional Recovery e.g., Maguire et al)

Question 15

Evaluating Localisation of Function - Weakness

Answer 15

Point: There is contradictory research.

Evidence: Research by Saygin et al. found that some patients displayed symptoms of Wernicke’s aphasia without any damage to this area.

Justification: This suggests that language comprehension is much more complex than originally thought. Further evidence has also been found which suggests some left-handed people process language in the right hemisphere.

Implication: This reduces the validity of the theory of localisation of brain function.

Question 16

Hemispheric Lateralisation

Answer 16

Lateralisation is the idea that the two halves of the brain are functionally different and that each hemisphere has functional specialisations, e.g., the left is dominant for language, and the right excels at visual motor tasks. The two hemispheres are connected through nerve fibres called the corpus callosum, which facilitate interhemispheric communication: allowing the left and right hemisphere to communicate with each other.

Question 17

Split-Brain Research

Answer 17

Sperry and Gazzaniga were the first to investigate hemispheric lateralisation with the use of split-brain patients.

Question 18

Aim

Answer 18

The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions.

Question 19

Method

Answer 19

• Natural experiment.
• An image/word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere).
• When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut).
• They conducted describe what you seek tasks, tactile tests and drawing tasks:

1. In the describe what you see task, a picture was presented to either the left or right visual field and the ppt had to simply describe what they saw.
2. In the tactile test, an object was placed in the patient’s left or right hand and they had to either describe what they felt, or select a similar object from a series of alternate objects.
3. In the drawing task ,ppts were presented with a picture in either their left or right visual field, and they had to simply draw what they saw.

Question 20

Findings

Answer 20

DWYS
1. Picture presented to RVF (processed by LH) - the patient could describe what they saw, demonstrating the superiority of the left hemisphere when it comes to language production.
2. Picture presented to LVF (processed by RH) - the patient could not describe what was shown and often reported that there was nothing present.

TT
1. Object placed in right hand (processed by LH) - the patient could describe verbally what they felt or they could identify the test object presented in the right hand by selecting a similar appropriate object, from series of alternate objects.
2. Object placed in left hand (processed by RH) - the patient could not describe what they felt and could only make wild guesses. However, the left hand could identify a test object by selecting a similar appropriate object, from a series of alternate objects.

DT
1. Picture presented to RVF (processed by LH) - While the right-hand would attempt to draw a picture, the picture was never as clear as the left hand, again demonstrating the superiority of the right hemisphere for visual motor tasks.
2. Picture presented to LVF (processed by RH) - the left hand would consistently draw clearer and better pictures than the right-hand (even though all the ppts were right-handed). This demonstrates the superiority of the right hemisphere when it comes to visual motor tasks.

Question 21

Conclusion

Answer 21

The findings of Sperry and Gazzaniga’s research highlights a number of key differences between the two hemispheres. Firstly, the left hemisphere is dominant in terms of speech and language. Secondly, the right hemisphere is dominant in terms of visual-motor tasks.

Question 22

Evaluating Split-Brain Research - Strength

Answer 22

Point: An advantage of brain lateralisation is its evolutionary advantage in increasing neural processing capacity (the ability to perform multiple tasks simultaneously).

Evidence: Rogers et al. found that in a domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators). using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions.

Justification: This provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks.

Question 23

Evaluating Split-Brain Research - Weakness

Answer 23

Point: An issue of many split-brain research is sampling.

Evidence:
- Rogers et al. - domestic chicken - cannot generalise to the human population.
- Sperry and Gazzaniga - only 11 ppts - split-brain procedure is rarely carried out now, meaning patients are difficult to come by which is a flaw of research into lateralisation - such studies often include very few ppts and often the research takes an idiographic approach.

Justification: Therefore, any conclusions drawn are representative only of those individuals who had a confounding physical disorder that made the procedure necessary and as for Rogers et al, the idea of brain lateralisation and how it can enhance brain efficiency for cognitive tasks cannot be applied to the human population as it was carried out on chickens.

Implication: This reduces the strength of split-brain research as it is often not generalisable to a wider, human population.

Question 24

Evaluating Split-Brain Research - Weakness

Answer 24

Point: Research has suggested that lateralisation changes with age.

Evidence: Szaflarki et al. found that language became more lateralized to the left hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of life.

Justification: This raises questions about lateralisation, such as whether everyone has one hemisphere that is dominant over the other and whether this dominance changes with age.

Implication: Therefore, this reduces the validity of the theory of lateralisation.

Question 25

Evaluating Split-Brain Research - Weakness

Answer 25

Point: It could be argued that language may not be restricted to the left hemisphere.

Evidence: Turk et al. discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information presented to either side of the brain.

Justification: This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.

Implication: Therefore, this is a weakness of the theory of lateralisation as it reduces its validity.

(Can also use this evaluation to refer to Plasticity & Functional Recovery)