Functional relationship between somatosensory cortex and specialized afferent pathways in the monkey

Previous work showed that the primate dorsal funiculus (DF) was necessary for tactile discrimination which entailed movement. The extra-DF spinal afferent fibers, by contrast, were sufficient for discrimination of tactile stimuli which did not require movement. This study investigated the association between various cortical regions and the specialized tactile roles of the separate afferent systems. Monkeys learned two sets of tasks, one of which was dependent on DF integrity, and the other was capable of mediation by the extra-DF pathways. The cortical distribution and processing of DF and extra-DF information has been defined here by whether or not these tasks were affected by lesions in the respective regions. Lesions in area 3b led to impairment of both tasks, but more severe and longer-lasting impairment of the DF tests. Lesions in areas 1, 5, or 7 were without effect on either type of function. Ablation of the forelimb region in area 2 selectively damaged only the DF discriminations. These results, in combination with the results of others which are considered here, suggest that (i) both the DF and the extra-DF tactile information converge into area 3b; (ii) the extra-DF information is then projected diffusely to widespread regions of the cortex which enables it to survive limited parietal ablations; and (iii) the DF information is transmitted compactly to a focal region in area 2.