Lateralization

What is lateralization?

Lateralization, also spelled lateralisation, is an asymmetry between the two cerebral hemispheres in the organization or contribution of particular brain functions. Language and visuospatial processing provide examples, but lateralization does not mean that a complex activity belongs exclusively to one side.

Examples of hemispheric specialization

Language activity is often more left-lateralized, while aspects of visuospatial processing are often more right-lateralized. The pattern varies across people and tasks; “more involved” does not mean “works alone.”

The left-brain/right-brain personality claim

In a study of resting-state brain connectivity in 1,011 people, Nielsen and colleagues identified lateralized networks but found no support for a general pattern of people having stronger left-brain or right-brain networks overall. The finding concerns connectivity in people aged 7–29; it is not a test of every cognitive function.

Descriptions that assign logic and mathematics to one hemisphere and emotion or holistic thought to the other oversimplify functional organization. Regional specialization does not justify classifying people as left-brained or right-brained, nor does it establish that one side is superior.

Communication between the hemispheres

The corpus callosum is a major bundle of nerve fibers connecting the hemispheres. Research with people whose corpus callosum was cut as part of treatment for severe epilepsy helped investigate hemispheric specialization and information sharing. These “split-brain” findings concern altered communication in a particular neurological setting; they do not divide the general population into two personality types.