Lateralization of brain function

Diagram of the human brain. — The human brain is divided into two hemispheres–left and right. Scientists continue to explore how some cognitive functions tend to be dominated by one side or the other; that is, how they are *lateralized*.
Right cerebral hemisphere
Left cerebral hemisphere

The lateralization of brain function (or hemispheric dominance or lateralization) is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. The median longitudinal fissure separates the human brain into two distinct cerebral hemispheres connected by the corpus callosum. Both hemispheres exhibit brain asymmetries in both structure and neuronal network composition associated with specialized function.

Lateralization of brain structures has been studied using both healthy and split-brain patients. However, there are numerous counterexamples to each generalization and each human's brain develops differently, leading to unique lateralization in individuals. This is different from specialization, as lateralization refers only to the function of one structure divided between two hemispheres. Specialization is much easier to observe as a trend, since it has a stronger anthropological history.

The best example of an established lateralization is that of Broca's and Wernicke's areas, where both are often found exclusively on the left hemisphere in the vast majority of people. Function lateralization, such as semantics, intonation, accentuation, and prosody, has since been called into question and largely been found to have a neuronal basis in both hemispheres. Another example is that each hemisphere in the brain tends to represent one side of the body. In the cerebellum, this is the ipsilateral side, but in the forebrain this is predominantly the contralateral side.