Hemispheric Lateralisation

Further Reading on handedness.

Why is there a dominance of right hander this pattern and been observed for over 5000 years. Animal tend to show an equal distribution between left and right pawed, whereas humans show a preference for the right hand. The two cerebral hemisphere process information differently, brain research has put forward the idea that left-handedness is the produced by abnormities in the bran such as a defect caused by a reduction of blood supply to the left hemisphere during the fatal growth. Damage to the left hemisphere can case a shift of dominant limb function to the right hemisphere. However these finding ate not see with premature birth, prolonged labour and breech birth. Another conception is that testosterone can slow down development in the left hemisphere in male foetus suggesting that high levels of testosterone is responsible for left handedness unsurprising this result was  unsubstantial.      

 There has been a debate that left – handedness many have genetic components. This argument claim that it is inherited, whereas left handed parent are more likely to have left handed children evidence to support this claim was adoption studies indicated that adopted children handedness  resembled their birth parent rather than their adopted parent. Additionally researcher  have stated that there is a single gene that in found in right hander and individual that do not have this gene exhibit random handedness however other have rejected this hypothesis because if both parent are left handed and left handedness was a recessive trait then all their children should be left handed. This show that there may be more than one gene involved or other factors may play a role.     

Handedness has many definitions, but is commonly known as the hand that a person uses to write. With this this context there has been debate about this vague definition. Other identifies it as the hand that performs the fastest and precisely, alternatively it can be seen as the hand that is preferred regardless of performances. There has been dispute about the different type of handedness, left or right. Whereas other feel that ambidexterity should also be included in the category. Furthermore there has been critique suggestion that there is two different type of ambidexterity. Paul Broca claim that the person handedness was the opposite side of the of the specialised area, this propose that a right handed person most likely have left hemisphere language dominance specialisation  however there has also been evidence to suggest that left hander also show dominance for language in the left hemisphere. While half of left handers use their right hemisphere, some left hander control writing completely and independently by the right hemisphere in the bran.

Summary of the Topic

The two cerebral hemisphere are not exactly alike. Each hemisphere have specialised functions, in addition some of the neural mechanisms are located primarily in one half of the brain. Paul Broca was the first to suggest that cognitive function is localised in the brain, for instance speech and language abilities showed dominance in the left hemisphere. Wernicke found other area in the left hemisphere that was responsible for language comprehension. Clinical reports have shown not hat around 70-95  of human have a left hemisphere language specialisation therefore around 5- 30 of humans have an abnormal pattern of specialisation  such as showing dominance of language in the right hemisphere or little literalised specialisation.