Week 8

Laterality in humans

The human body seems symmetrical in external and internal anatomy, but looking closer, we can observe high levels of asymmetry. Even the brain exhibits a great level of asymmetry, anatomically as well as functionally. Several studies have reported for the left-hemisphere to be rather rational, verbal, linear and analytic, whereas the right-hemisphere seems to be emotional, spatial, holistic and intuitive. Arthur Wigan (1844) was one of the first scientists arguing for our hemispheres to be independent entities. Following, researchers examining split-brain patients supported that statement reporting patients acting as having two separate brains. Further research suggested the left-hemisphere to be mainly involved in language whereas the right-hemisphere showed more activation during visuospatial tasks.

Several single-word studies showed great involvement of the left-hemisphere, however, when expanding to sentences and discourse comprehension, the right hemisphere also seemed to show involvement. Therefore it has been speculated that the right-hemisphere is involved in the sentence's thematic sense. Bottini et al. (1994) found for the right-hemisphere to process metaphors and irony.

A study by De Renzi (1982) argued for the right-hemisphere to be involved in visuospatial abilities. Other scientists however argued for a less defined cut, since the right-hemisphere showed high activity during mental rotation processes, but the left-hemisphere seemed to be involved in other visual tasks. (212 words). Harris et al. (2000) then discovered the right posterior parietal lobe to process extreme rotations, with high levels of decision-making, whereas the left side might rather be involved in simple visual tasks.

In conclusion it can be said, that most cognitive functions are not processed in one hemisphere only. Moreover, their involvement in the task differs in gender and handedness.