The neocortex and visual placing in rats

Hooded rats were tested for visual and tactual placing responses prior to and 3 weeks after partial or total neocortical ablation. An operational scaling technique was used to evaluate placing responses in terms of latency and extent of response. Removal of the anterior neocortex was followed by transient retardation of visual placing and by loss of tactual placing. Removal of the posterior neocortex resulted in loss followed by eventual recovery of visual placing but had no effect on tactual placing, and recovery could not be attributed to sparing of some portion of the area striata. Removal of all neocortex, except for small portions adjacent to the rhinal sulcus, resulted in loss of both tactual and visual placing responses, but visual orientation responses persisted. Further experimentation indicated that recovery of visual placing was possible after nearly complete ablation of the neocortex if extensive practice trials were given or if the lesion was performed in two separate stages with practice interpolated between stages. A tendency to recover accompanied repeated administrations of amphetamine, but this was not reliable. Recovery, when observed, appeared to be a function of practice because performance increased incrementally over 20 days of testing rather than occurring spontaneously. It was concluded that although both anterior and posterior neocortex are normally involved in, and certainly enhance, visual placing behavior in rats, neither seems necessary for such behavior to occur.