Lateralisation

• The idea that different hemispheres might have different specialisations can be traced back to Marc Dax, a French Doctor. • He treated patients who’d lost the ability to speak. • He observed in every case there was damage in the left hemisphere and no patients had experienced right-hemisphere damage, suggesting language was located in the left hemisphere

Refers to how the two halves of brain aren’t exactly alike. Each hemisphere has functional specialisations.

Info received by one hemisphere is sent to the other through connecting bundles of nerve fibres, like the corpus callosum

• When, in treatment of severe epilepsy, surgeons cut the bundle of nerve fibres that formed callosum. • The aim was to prevent the violent electrical activity that accompanies epileptic seizures crossing from a hemisphere to the other. • Patients who underwent this surgery are referred to as ‘split-brain’ patients

• Lateralisation appears to increase neural processing capacity • By using one hemisphere to engage in a task, the other hemisphere to free to engage in another function. However, little empirical evidence has showed that lateralisation confers any advantage to brain functionality in humans. • However, Rogers et al found that in domestic chicken, brain lateralisation is associated with enhanced ability to perform 2 tasks simultaneously. • This provides some evidence that brain lateralisation enhances brain efficiency in cognitive tasks that require the use of both hemispheres

• There are disadvantages with hemispheric lateralisation • e.g. architects and mathematically gifted tend to have better right-hemispheric skills but are more likely to be left-handed and to suffer higher rates of allergies and immune system problems. • Tonnessen et al found a small, significant relationship between handedness and immune system disorders, suggesting that the same genetic processes that lead to laterlisation may affect the development of immune system • Morfit and Weekes supported this, finding that left handers were more likely to have immune system disorders in their immediate families than did right-handers

• Lateralisation of function changes with normal ageing • Lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults . e.g. Szaflarski et al found language become more lateralised to the left hemisphere with increasing age in children, but after 25, lateralisation decreased with each decade of life • It’s difficult to know why, but one possibility is that using extra processing resources of the other hemisphere may compensate for age-related declines in function