Biopsychology - Brain Localisation and Lateralisation

Question 1

What is the holistic theory of the brain? What was it replaced with?

Answer 1

Scientists in the early 19th century supported the holistic theory that all parts of the brain were involved in the processing of thought and action.

But specific areas of the brain were later linked with specific physical and psychological functions (localisation theory).

If an area of the brain is damaged through illness or injury, the function associated with that area is also affected.

Question 2

What is localisation of function?

Answer 2

The idea that different parts of the brain perform different behaviours, processes or activities and are involved with different parts of the body. It follows then, that if a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected.

Question 3

What is lateralisation?

Answer 3

The brain is divided into two symmetrical halves called left and right hemispheres. Some of our physical and psychological functions are controlled or dominated by a particular hemisphere - this is called lateralisation.

Question 4

Which side of the brain controls which side of the body?

Answer 4

As a general rule, the activity on the left-hand side of the body is controlled by the right hemisphere and activity on the right-hand side of the body by the left hemisphere.

Question 5

What is the cerebral cortex?

Answer 5

The outer layer of both hemispheres is the cerebral cortex. It is what separates us from other animals because the human cortex is much more developed. The cortex appears grey due to the location of cell bodies (hence “grey matter” to describe the surface appearance of the brain).

Question 6

How is the cortex subdivided?

Answer 6

The cortex of both hemispheres is sub-divided into four lobes which are named after the bones beneath which they lie: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe. Each one is associated with different functions.

Question 7

What is the motor area?

Answer 7

At the back of the frontal lobe (in both hemispheres) is the motor area which controls voluntary movement in the opposite side of the body. Damage to this area of the brain may result in a loss of control over fine movements.

Question 8

What is the somatosensory area?

Answer 8

An area of the parietal lobe that processes sensory information such as touch. The amount of somatosensory area devoted to a particular body part denotes its sensitivity.

Question 9

What is the visual area?

Answer 9

A part of the occipital lobe that receives and processes visual information.

Each eye sends information from the right visual field to the left visual cortex, and from the left visual field to the right visual cortex. So damage to the left hemisphere, for example, can produce blindness in the right visual field of both eyes.

Question 10

What is the auditory area?

Answer 10

Located in the temporal lobe and concerned with the analysis of speech-based information. Damage may produce partial hearing loss - the more extensive the damage, the more serious the loss.

Question 11

What is Broca’s area?

Answer 11

An area of the frontal lobe of the brain in the left hemisphere (in most people) responsible for speech production.

Damage to this area causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency. Broca’s patients may have difficulty finding words and naming certain objects.

Patients with Broca’s aphasia have difficulty with prepositions and conjunctions.

Question 12

What is Wernicke’s area?

Answer 12

An area of the temporal lobe (encircling the auditory cortex) in the left hemisphere (in most people) responsible for language comprehension.

Patients produce language but have problems understanding it, so they produce fluent but meaningless speech.

Patients with Wernicke’s aphasia will often produce nonsense words (neologisms) as part of the content of their speech.

Question 13

What are the features of the left hemisphere?

Answer 13

• controls right side of body
• logic and language skills
• conscious thoughts
• speech (Broca’s area)
• reasoning
• science and maths
• written
• number skills
• right-hand control

Question 14

What are the features of the right hemisphere?

Answer 14

• controls left side of the body
• creative skills
• motor tasks
• unconscious thoughts
• facial recognition (inability = prosopagnosia)
• imagination
• intuition
• insight
• holistic thought
• music awareness
• art awareness
• spatial awareness
• left-hand control

Question 15

What is the corpus callosum?

Answer 15

The two hemispheres are connected through nerve fibres called the corpus callosum which facilitate interhemispheric communication.

Question 16

What are the strengths of localisation of function?

Answer 16

• brain scan evidence of localisation
• neurosurgical evidence
• case study evidence

Question 17

What are the weaknesses of localisation of function?

Answer 17

• existence of contradictory research
• neural plasticity challenges the localisation theory
• case study evidence

Question 18

What brain scan evidence is there of localisation?

Answer 18

Peterson et al. used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during a reading task, suggesting that these areas of the brain have different functions.

Similarly, a study of long-term memory by Tulving et al. revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. There now exists a number of highly sophisticated and objective methods for measuring activity in the brain which provide sound scientific evidence of localisation of brain function.

Question 19

What neurological evidence is there for localisation?

Answer 19

Neurosurgery is used in extreme cases of OCD and depression. Surgically removing or destroying areas of the brain to control aspects of behaviour was developed in the 1950s by Walter Freeman - though these early attempts were brutal and imprecise.

Dougherty et al. (2002) reported on 44 OCD patients who had undergone a cingulotomy - a neurosurgical procedure that involves lesioning of the cingulate gyrus. At post-surgical follow-up after 32 weeks, 1/3 had met the criteria for successful response to the surgery and 14% for partial response.

The success of procedures like this strongly suggests that symptoms and behaviours associated with serious mental disorders are localised.

Question 20

What case study evidence is there for localisation?

Answer 20

Phineas Gage

• rod
• changed personality (temperament) from calm and reserved to quick-tempered and rude
• suggests the frontal lobe may be responsible for regulating mood
• specific parts of the brain perform specific functions

Question 21

What case study evidence is there against localisation?

Answer 21

Jodie Miller

• epilepsy
• removed right hemisphere
• left took over

Question 22

How is Lashley’s research a weakness of localisation?

Answer 22

The work of Karl Lashley (1950) suggests that higher cognitive functions, such as the processes involved in learning, are not localised but distributed in a more holistic way in the brain.

Lashley removed areas of the cortex (between 10 and 15%) in rats that were learning a maze. No area was proven to be more important than any other area in terms of the rats’ ability to learn the maze.

The process of learning appeared to require every part of the cortex, rather than being confined to a particular area. This seems to suggest that learning is too complex to be localised and requires the involvement of the whole brain.

However, animal research has limitations.

Question 23

How is plasticity/cortical remapping a weakness of localisation?

Answer 23

When the brain has become damaged and a particular function has been compromised or lost, the rest of the brain appears able to reorganise itself in an attempt to recover the lost function.

Lashley described this as the law of equipotentiality whereby surviving brain circuits ‘chip in’ so the same neurological action can be achieved.

Although this does not happen every time, there are several documented cases of stroke victims being able to recover those abilities that were seemingly lost as a result of the illness.

Question 24

What are the key features of split-brain research?

Answer 24

• hemispheric lateralisation
• split-brain studies involved a unique group of individuals
• Sperry devised a unique procedure to test his split-brain patients
• describing what was seen
• recognition by touch
• composite words and matching faces

Question 25

What is hemispheric lateralisation?

Answer 25

Concerns behaviours controlled by just one hemisphere.

Language is an example of hemispheric lateralisation (usually controlled by the left hemisphere).

Question 26

Who did split-brain studies involve?

Answer 26

Sperry (1968) sought to demonstrate that the two hemispheres were specialised for certain functions and could perform tasks independently of one another.

Normally the hemispheres are connected by the corpus callosum and a few other structures. A commissurotomy is an operation to cut the corpus callosum and is sometimes performed to control epileptic seizures.

Sperry studied a group of epileptics who had the operation.

Question 27

What procedure did Sperry use?

Answer 27

An image or word is projected to a patient’s RVF (processed by LH) and another image to the LVF (processed by RH).

In the normal brain, the corpus callosum ‘shares’ information between both hemispheres. In the split brain, the information cannot be conveyed from the chosen hemisphere to the other.

Question 28

What results were found when describing what was seen?

Answer 28

Objects shown to:

• RVF: patient easily describes what is seen
• LVF: patient says “there’s nothing there”

Can’t describe objects in LVF because RH usually lacks language centres. Messages received by RH are normally relayed via the corpus callosum to language centres in LH.

Question 29

What results were found when recognising by touch?

Answer 29

Objects shown to LVF:

• could not name them but could select a matching object using left hand (connected to RH receiving information from LVF)
• left hand could also select an object that was associated with image presented to the LVF (e.g. ashtray selected in response to a picture of a cigarette)

In each case, the person could not verbally identify what they had seen (because the LH is needed for this) but could ‘understand’ what the object was (using the RH) and select the corresponding object.

Question 30

What results were found when given composite words and trying to match faces?

Answer 30

Two words presented on either side of the visual field (e.g. ‘key’ presented to the left and ‘ring’ to the right). Patient:

• writes ‘key’ with left hand (goes to RH linked to LVF)
• says the word ‘ring’ (RVF linked to LH)

Composite picture made up of two different halves of a face was presented (one half to each hemisphere):

• LH dominated the verbal description
• RH dominated the selection of a matching picture

Question 31

What are the strengths of split-brain research into hemispheric lateralisation?

Answer 31

• it shows lateralisated brain functions
• scientific methodology to Sperry
• Sperry’s work started a debate about the nature of the brain

Question 32

What are the weaknesses of split-brain research into hemispheric lateralisation?

Answer 32

• issues with generalisation in relation to Sperry’s work

- differences in hemispheric functions may be overstated

Question 33

How does split-brain research show lateralised brain functions?

Answer 33

The left hemisphere is analytical and verbal (‘the analyser’) and the right is adept at spatial tasks and music (the ‘synthesiser’).

The right hemisphere can only produce basic words and phrases but contributes emotional content to language.

Recent research suggests this distinction may be too simplified and several tasks associated with one hemisphere can also be carried out by the other.

Question 34

How is Sperry’s methodology scientific?

Answer 34

Sperry’s carefully standardised procedure of presenting visual information to one hemispheric field at a time was quite ingenious.

Participants started at a fixed point with one eye. An image was flashed up for 0.1 seconds, so the patient had no time to move their eyes over the image and spread the information across both sides of the visual field or both sides of the brain.

This allowed Sperry to vary aspects of the basic procedure and ensure only one hemisphere received information at a time - a very useful and well-controlled procedure.

Question 35

How did Sperry’s work start a debate about the nature of the brain?

Answer 35

Sperry’s work triggered a theoretical and philosophical debate about the nature of consciousness and the degree of communication between the two hemispheres in everyday functioning.

Pucetti (1977) suggested the hemispheres are so functionally different they represent a form of duality in the brain (we are effectively two minds). Others argued the two hemispheres are highly integrated and work together in most tasks.

The value of Sperry’s work is in prompting this complex debate.

Question 36

Why are there issues with generalisation in relation to Sperry’s work?

Answer 36

Many researchers have said these findings cannot be widely accepted, as split-brain patients are such an unusual sample of people.

Only 11 patients took part in all variations and all had a history of seizures. This may have caused unique changes in the brain that influenced the findings.

This limits the extent to which the findings can be generalised to normal brains, reducing the validity of the conclusions.

Question 37

How may differences in hemispheric functions be overstated?

Answer 37

A legacy of Sperry’s work is a growing body of pop-psychological literature that oversimplifies and overstates the difference in function between the two hemispheres.

Modern neuroscientists argue these distinctions are not at all clear-cut. Many behaviours that are typically associated with one hemisphere can be performed by the other when situations require.

The apparent flexibility of the two hemispheres suggests some of the conclusions drawn by Sperry may be too simplistic.