Patterns of Hemispheric Asymmetry Set Against Clinical Evidence

Abstract

The notion of hemispheric asymmetry has provided a convenient and productive framework for the study of brain-behaviour relationships. The morphology of the brain encourages this ‘sagittal’ viewpoint. Hypotheses vary from those envisaging a relatively sharp division of function to those allocating a more equal partnership to the left and right hemisphere. Evidence for a right/left hemisphere dichotomy abounds in the neuropsychological literature of the last three decades and can be traced to classical Greece. Thus, Soranus: ‘there are two brains in the head, one of which gives understanding, and another which provides sense perception. That is to say, the one which is lying on the right side is the one that perceives; with the left one, however, we understand’ (Lokhorst, 1982). Advocates of the partnership notion can be found in the nineteenth century. Gall envisaged the brain as ‘a double organ with integrant parts — symmetrical, duplicate, and subject to genetic and ontogenetic influences’ (cited by Harrington, 1985). The imaginative physician, Wigan (1844) considered the hemispheres to be ’two perfect organs of thought and volition — each, so to speak, a sentinel and a check on the other.’ Although the hemispheres were thought to duplicate their intrinsic cognitive capacities, there were nevertheless slight inequalities of form, energy and function: thus in Wigan’s view, the left hemisphere was ‘superior in power’ — hence ‘the superior efficacy of the right hand as an instrument of volition.’ Perhaps the two approaches are not as discordant as may at first appear.