You may have heard the saying that people are either ‘left-brained’ or ‘right-brained’, meaning that one of the two brain hemispheres is dominant.
It is true that different brain regions show specialisation for particular tasks, such as language or visual processing, but there is no evidence that people have one dominant hemisphere or that hemisphere specialisation is linked to personality.
The two hemispheres of the brain are connected by a bundle of nerve fibres called the corpus callosum, allowing the two hemispheres to communicate and work together. This makes it difficult for scientists to study one hemisphere in isolation. Much of our understanding of the functional differences between hemispheres has come from studying stroke patients and so-called ‘split-brain’ patients, whose corpus callosum has been severed, usually as a treatment for severe epilepsy.
These studies showed, for example, that the main language centres of the brain are usually located in the left hemisphere, and that each hemisphere is responsible for the motor functions of the opposite side of the body. These real differences might be the origin of the left-brain right-brain myth. However, activities like maths or art are so complex that they require contributions from both hemispheres.
Brain imaging and electroencephalography (EEG) have identified hemisphere asymmetries for particular tasks, such as word comprehension and forming mental images, indicating that different hemispheres have different strengths and weaknesses. But the right hemisphere is still capable of ‘left-brained’ tasks, and vice versa.
These task-specific asymmetries don’t appear to translate into the dominance of one hemisphere over the other, either: a 2013 study of more than 1,000 children and adults found no evidence for overall left- or right-hemisphere dominance in brain connectivity.
Asked by: Adam Jarrett, Ipswich
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