An experimental investigation of the parietal lobes and temperature discrimination in monkeys

Seven groups of 3 monkeys each were given preoperative training over a series of thermal discrimination tasks of increasing difficulty to use eventually their left hands to detect a 1 degree C difference. One group served as an unoperated control (C), and the others were subjected to the following lesions: bilateral SI-bilateral SII; bilateral SI; bilateral SI-contralateral SII; bilateral SII-bilateral posterior parietal; bilateral parietal lobectomy; and contralateral parietal lobectomy. The groups were then tested again on the same tasks. No group showed any difficulty with differences larger than 12 degrees C, and groups 2, 4, 6 and C showed no statistical differences in their preoperative and postoperative number of trials to criteria for any of the temperature tasks. However, groups 1, 3 and 5 had considerable difficulty making discriminations ranging between 3 and 12 degrees C; and, although their postoperative performances were not significantly different from one another, they took statistically more trials to discriminate the 1 degree C difference in post- than in preoperative testing. Following extensive retraining, all but one of the subjects in the latter groups were able to detect the 1 degree C difference. It was concluded that the bilateral SI and contralateral SII areas play important roles in the monkey's ability to discriminate fine temperature differences with its hand, but that these areas are not essential to this capacity. It was also concluded that the monkey's parietal cortex plays little or no role in perceiving and reacting to noxious thermal stimulation applied to the hand.