Abstract

The human brain is divided into two hemispheres, right and left, that are joined by a thick ‘cable’ of neural fibres called the corpus callosum. It has long been observed that injury to the left hemisphere in the average adult damages speech, speech comprehension, and reading, and causes paralysis on the right side of the body. Injury to the right hemisphere, on the other hand, seems to leave linguistic capabilities intact, but causes paralysis on the left side of the body. These observations have given rise to the twin concepts of contralaterality of hemispheric control and cognitive specialization of hemispheric function. As far back as the nineteenth century, it was recognized that the left hemisphere’s specialty was language. Pioneering British neurologist John Hughlings Jackson asserted in 1868 that the left hemisphere was the ‘leading side’ in most people, responsible for the control of speech and will. In the decade of the 1940s, French neurologist Henry Hecaen and British psychologist Oliver Zangwill demonstrated that the right hemisphere, far from being passive, controlled visuospatial processing