Dorsolateral prefrontal cortex lesions and discrimination of movement-produced cues by rhesus monkeys

Rhesus monkeys were trained on a conditional discrimination in which sequences of either 32 or 64 lever presses served as discriminative stimuli. For half the subjects, reinforcement was contingent upon choice of a red response key following a sequence of 32 presses (FR 32), and a white key after FR 64, with the position of the two key colors randomized across trials. The remaining subjects were reinforced for left key presses after FR 64, and right key presses after FR 32, with key color again randomized across trials. Ablation of dorsolateral prefrontal cortex resulted in postoperative deficits in all subjects, although 6 of 8 eventually remastered the task. This recovery was investigated in a second experiment, in which psychophysical functions were generated by varying the length of the shorter FR. Although dorsolateral lesions again produced a severe disruption in performance, the post-operative functions eventually obtained were identical to the preoperative functions. This pattern of marked impairment in retention of fixed ratio discriminations, but no change in asymptotic capacity, suggests participation of dorsolateral prefrontal cortex in processing kinesthetic information, possibly analogous to the role of inferior temporal cortex in processing visual information.