The lateral organization of the gustatory pathway in man is incompletely understood. Majority of the studies support an uncrossed projection from each side of the tongue to the cortex, but reports of an opposite crossed organization continue to appear in the neurological literature. We studied the lateral organization of the gustatory pathway in normal controls, a man with a complete callosal agenesis, and a man with a complete section of the corpus callosum, a right anterior-frontal lesion, and language in the left hemisphere. Sapid solutions were applied to one or the other side of the tongue, and subjects reported the taste of the stimulus either verbally or by manually pointing to the name of the taste. There were no differences in accuracy and reaction time between the right and left hemitongues of the controls and the genetically acallosal observer. By contrast, the callosotomy subject showed a constant marked advantage of the left hemitongue over the right for both accuracy and speed of response, though performance with right stimuli was clearly above chance. The left advantage can be attributed to the left hemisphere being favored by the essentially verbal nature of the task, or to the presence of a lesion in cortical gustatory areas in the right hemisphere, or to both factors. Whichever of these hypotheses turns out to be correct, the results unequivocally reject the notion of an exclusively crossed organization of the gustatory pathway from the tongue to the cortex, and favor the notion of a bilaterally distributed organization of this pathway with a marked predominance of the uncrossed over the crossed component.

Twelve normal controls, twelve left-brain-damaged patients, and thirty-six right-brain-damaged patients with or without tactile extinction or tactile neglect were asked to report light touches delivered to the left or the right hand or simultaneously to both hands. The hands could be in anatomic position or one hand could cross over the other. Moreover, the two hands could be in the left or the right hemispace or across the corporeal midline. Controls and nontactile-extinction groups performed better when the hands were in anatomical than in crossed position. By contrast, patients with tactile extinction detected contralesional stimuli with higher accuracy in crossed than in anatomical position. This result suggests that, in these patients, impairments in detecting contralesional stimuli can be due not only to sensory but also to spatial factors contingent upon the position of the hands. There was no interaction between the effect of crossing the hands and the hemispace where the crossing took place. This suggests that coding the position of a hand as left or right does not necessarily occur in relation to the bodily midline, but it may arise from the computation of the position of the other hand.