Deafferentation and axotomy of neurons in cat striate cortex: time course of changes in binocularity following corpus callosum transection.

Single neurons were recorded in the callosal terminal and cell zones of area 17 in the cat to assess the time course of changes in the proportion of binocular neurons produced by corpus callosum transection. The callosal terminal zone contains all the degenerating terminals in area 17 after corpus callosum transection. The callosal cell zone contains all the cells in area 17 which contribute axons to the corpus callosum. The cell zone is larger than, and partially overlaps, the callosal terminal zone. After corpus callosum transection there was an initial change in ocular dominance of neurons in both callosal zones. This initial change was followed by a reduction in the proportion of binocular neurons in both zones. This reduction became maximal 2-4 weeks after transection. In the callosal terminal zone, binocularity did not recover even at the longest postoperative periods examined (31-42 weeks). In the part of the callosal cell zone outside of the callosal terminal zone, the proportion of binocular neurons began to recover after 5 weeks and was at normal levels at the longest survival periods studied. Corpus callosum transection deafferents and axotomizes cells in the callosal terminal zone and, since central neurons do not regenerate their long-ranging axons, the combined effects of deafferentation and axotomy in this zone are permanent. The callosal cell zone outside of the callosal terminal zone contains axotomized cells and no degenerating terminals following transection. The recovery of binocularity in this region may be attributed to the transient changes which axotomized cells undergo. The zone which contains no callosal cells or terminals is unaffected by transection of the corpus callosum.