The role of the dorsal funiculus of the primate in tactile discrimination

Abstract

The critical role of the dorsal funiculus for tactile discriminations requiring active exploration of the stimulus object was tested in the monkey. Pairs of discriminanda (patterned disks) were constructed with geometric designs of such size and shape as to require active palpation for successful discrimination. For comparison, other discriminanda with tactile qualities which could be recognized by a more passive response topography were also examined. Section of the dorsal funiculus resulted in severe, long-lasting deficits in discrimination of the patterned disks, while discrimination of the tactile qualities not requiring active exploration was retained. No significant motor impairment was observed. Lesions in the spinothalamic or spinocervical systems had no effect on either type of cutaneous discrimination. The results support the view that the afferents from the monkey hand which travel in the dorsal funiculus are critically and possibly exclusively involved in the perception of tactile stimuli requiring a spatiotemporal transformation by the introduction of movement. It is further suggested that such movement need not be self-initiated.