Behavioral effects of SI versus SII cortex ablations on tactile orientation-localization and postural reflexes of rats.

Ten rats were observed, before and after selective unilateral ablation of the SI and/or SII cortical area, for the ability to turn toward tactile stimuli to head, limbs, or trunk. Placing and hopping postural reflexes were also observed. SI damage caused greater contralateral deficits than SII damage in all these behavioral measures; combined ablation of SI plus SII caused the greatest contralateral deficits in all measures. Partial recovery of all behaviors was observed during six postoperative test sessions, spanning 2 months. In contrast to these rats, cats studied in earlier experiments in this laboratory had shown a double dissociation, with SI damage followed by contralateral deficits in posture and movement but not passive touch, and damage to SII plus subjacent cortex by contralateral deficits in passive touch but only very small deficits in posture and movement. In other species comparisons, normal rats oriented as vigorously as do cats to tactile cues and, like cats, showed tactile responsiveness in orientation-localization greater rostrally than caudally. In both species wrong-way orientations were occasionally observed during the early postoperative period following the largest unilateral lesions. Unoperated albino rats oriented much less readily than do unoperated cats toward appetitive auditory or visual cues signaling availability of food. An accompanying theoretical review paper further examines the nature of passive and active touch in terms of these and other comparative findings.