Brain Lateralisation

Question 1

What is brain lateralisation

Answer 1

The term brain lateralisation refers to the idea that the two halves of the human brain are not exactly alike. Each hemisphere has functional specialisations - For example, research has shown that the left hemisphere is dominant for language and the right hemisphere with visual-motor tasks.

Question 2

Contralateral meaning

Answer 2

The brain is 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.
This means if a person has a stroke in the motor cortex of the right hemisphere, it will be the left side of the body which is affected by the stroke. It is also the case that what you see in your right visual field is processed by your left hemisphere and although you gather auditory information from both ears, the information from the left ear is dealt with predominantly by the right hemisphere of the brain.
Taste and smell are also contralateral: taste from your left side of your tongue and smells from your left nostril are processed in the right hemisphere.
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. For example, 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 3

What is the right hemisphere dominant for

Answer 3

recognising emotion in others (Narumoto et al., 2001). For example, studies have shown that if a photo of a face is split so that half is smiling and the other half is neutral, the emotion displayed on the left hand side of the picture is the emotion that is recognised by the participant.
The right hemisphere is also dominant for spatial relationships – this was supported by a case study of a women who had her right hemisphere damaged. This woman 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 4

How can we talk about things presented to the right hemisphere if language is lateralised to the left hemisphere

Answer 4

The answer to this question is that the two hemispheres are connected. In other words, there is a part in the brain known as 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 5

How can you investigate the diff abilities of the two hemispheres

Answer 5

When ur treating patients w 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 6

Strengths of lateralisation

Answer 6

1. 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
2. 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. For example, 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 7

Weaknesses of lateralisation

Answer 7

1.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.
2. 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)