Effect of prior experience on bar-pressing in rats without neocortex

Rats in which all neocortex had been surgically removed produced similar patterns of performance to those previously established for rabbits with total neocortical ablations in a bar-pressing task for food reward. The animals deprived of neocortex developed inefficient patterns of food-tray related behaviours and a limit to their bar-pressing performance for intermittent rewards in the region of 4-10 presses per reward. The lesioned animals were also unable to form a sequential brightness discrimination on a GO-NOGO schedule using a bar-press response. Neither prior experience of other instrumental learning situations nor experience of working in the same apparatus and using the same instrumental response were sufficient to improve subsequent bar-press performance for intermittent reward in the neocortically lesioned animals. Previous success in improving such performance by pretraining procedures designed to facilitate identification of the part of the apparatus to be manipulated by the animal cannot easily be explained, therefore, on the basis of such incidental factors as increased behavioural sophistication or of increased familiarity with the apparatus and the instrumental response itself. The data are consistent with the view that the neodecorticate's difficulty in the bar-pressing situations for intermittent rewards is due to inadequate identification of cues associated with the object to be manipulated rather than to an associative learning deficit.