L7 - Brain Lateralisation

Question 1

Brain lateralisation

Answer 1

• refers to the idea that the two halves of the human brain are not exactly alike.
• Each hemisphere has functional specialisations e.g. research has shown that the left hemisphere is dominant for language and the right hemisphere with visual-motor tasks.

Question 2

What is a feature of the brain?

Answer 2

• contralateral (opposite sides) in most people
• so parts of the left hemisphere deal with the right side of the body and the right hemisphere does the same for the left side of the body

Question 3

What senses are contralateral

Answer 3

• taste
• smell
• sight
• hearing

Question 4

What senses are contralateral

Answer 4

• taste
• smell
• sight
• hearing

Question 5

What does it mean to be lateralised

Answer 5

• If a function is dealt with by one hemisphere it is said to be lateralised.
• Furthermore as the two hemispheres are not symmetrical, this means the functions of the two must also differ.
  E.g. Paul Broca demonstrated how damage to the left hemisphere led to language deficits but damage to the right hemisphere did not produce any language deficits.

Question 6

What is the right hemisphere dominant in?

Answer 6

The right hemisphere is also dominant for spatial relationships
- supported by a case study of a women who had her right hemisphere damaged, would often get lost even in familiar situations, unless she had verbal instructions which contained a distinguishable visual feature to follow such as ‘turn right at the red house with the ‘turret’.
-This suggests that the right hemisphere deals with spatial information (Clarke et al., 1993).

Question 7

How are we able to process things from different hemispheres?

Answer 7

• the two hemispheres are connected. the corpus callosum that acts as the communicator between both hemispheres.
• This means that regardless of what hemisphere processes the information, because the two hemispheres communicate with each other via the corpus callosum we are able to process information holistically.

Question 8

How to investigate the two hemispheres

Answer 8

• The chance to investigate the different abilities of the two hemispheres came about when treating patients with severe epilepsy
• Surgeons cut the bundle of nerve fibres that formed the corpus callosum – this was carried out so that the violent electrical activity that accompanied the epileptic seizures crossing from one hemisphere to the other.
  -This then meant that had broken the communication means from one hemisphere to the other
• . By doing this, researchers had the opportunity to study brain lateralisation. This kind of research is known as SPLIT-BRAIN research.

Question 9

Evaluation of lateralisation

Answer 9

strengths
- understand locations of specific functions
- can study left handedness
weaknesses
- changes with age
- brain plasticity

Question 10

Understand locations of specific functions

Answer 10

• Studying lateralisation helps us to understand how specific functions are located on specific sides of the brain so that we can understand more about multi-tasking
• Thus lateralisation frees the other hemisphere to engage in a different task.
• Rogers et al. (2004) found that in the domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously – finding food and being vigilant for predators.
• This finding does provide some evidence that brain lateralisation enhances brain efficiency in cognitive tasks that demand the simultaneous but different use of both hemispheres

Question 11

Can study left-handedness

Answer 11

• Lateralisation means we can study left handedness (people who have right hemispheric dominance) and why they may be prone to allergies and illness.
• People who are left handed (showing right hemispheric dominance) tend to suffer higher rates of allergies and problems with the immune system.
  E.g. Tonnessen et al (1993) found a small but significant relationship between handedness and immune disorders suggesting a link between lateralisation and the development of the immune system supporting the idea of brain lateralisation.

Question 12

Can study left-handedness

Answer 12

• Lateralisation means we can study left handedness (people who have right hemispheric dominance) and why they may be prone to allergies and illness.
• People who are left handed (showing right hemispheric dominance) tend to suffer higher rates of allergies and problems with the immune system.
  E.g. Tonnessen et al (1993) found a small but significant relationship between handedness and immune disorders suggesting a link between lateralisation and the development of the immune system supporting the idea of brain lateralisation.

Question 13

Changes with age

Answer 13

• Lateralisation changes with age and is therefore not set in stone – for example Szaflarski et al. (2006) found that language became more lateralised to the left hemisphere up to the age of 25 but decreased after that.
• This suggests that we should be cautious in assuming that brain lateralisation is set in stone throughout life as research has suggested that lateralisation is only relevant up to a certain age.

Question 14

Doesn’t explain brain plasticity

Answer 14

• Lateralisation does not explain brain plasticity since studies have shown how having one hemisphere damaged does not mean that the individual will have an abnormal brain – it has been shown that the other hemisphere can actually take over and do the job of both hemispheres.
• This suggests that brain plasticity can overcome potential limitations associated with lateralisation. (see the case study on EB by Danielli et al (2013).

Question 15

What’s left hemisphere responsible for?

Answer 15

Language

Question 16

What’s right hemisphere responsible for

Answer 16

Visual/spatial & motor tasks

Question 17

EB case study

Answer 17

• Danelli et al (2013) studied an Italian boy named EB who was operated on at the age of 2.5 years to remove a large benign tumour from his left hemisphere.
• After the operation, EB lost all his linguistic abilities. He was right handed and therefore his language was probably located in the left hemisphere. (Supports lateralisation)
• He underwent an intensive rehabilitation programme and his language abilities started to improve at age 5. They continued to do so over the next three years to the point when he no longer had any language difficulties.
• When they tested him at age 17 compared to ’normal’ controls, they found that his right hemisphere had compensated for the loss of the left hemisphere and that his linguistic abilities were functioning well.
• This study supports the idea of functional recovery in the recruitment of homologous areas (on the opposite side of the brain e.g. EB’s right hemisphere compensating for the damage to the left hemisphere.)