ABSTRACT
Neuropsychological research on normal subjects has become subdivided into three areas. They are psychophysiological techniques, the electroencephalograph, with its poor spatial resolution; 'scanning' and blood flow techniques, glucose metabolism and regional cerebral blood flow methods, with their poor temporal resolution; and split-field techniques, tachistoscopic and dichotic methods, with their unnatural stimulus presentation. An excitatory theory of callosal functions – which implies the approximate duplication of neural information in both hemispheres — would alone predict only minimal effects due to callosal transection. Perhaps the least conclusive of all the arguments concerning callosal function are based upon findings on the normal, intact brain. The pharmacological implications of a brainstem asymmetry are of course appealing to the clinician, but currently the alternative view of the causal mechanisms involved seems equally viable. Patients in which the corpus callosum is severed or absent from birth, and patients with unilateral brain damage will probably provide the conditions most suitable for testing hypotheses concerned with callosal functions.
