Visual Learning and Retention after Ablation of Inferotemporal Cortex in Dogs

Abstract

Based on instrumental conditioned avoidance responses, retention and acquisition of visual discrimination of flicker frequencies were studied in 15 dogs with surgical lesion limitted to the bilateral neocortecies of polus temporalis and gyrus temporalis inferior. In addition, the differential threshold of visual performance, i.e., the least difference of flicker frequencies to be discriminated was determined at various pre- and postoperative stages in order to investigate the capacity to form learning sets, i.e., learn how to learn. Histological control of the ablated areas was made by a conventional method.
The results obtained are as follows:
1. The retention of the preoperatively learned discrimination was markedly reduced by bilateral ablation of the inferotemporal cortex, while it was not affected in the control animals which underwent bilateral removal of gyrus ectosylvius or unilateral lesion of the inferotemporal lobe.
2. For the inferotemporal-operated dogs, learning was further more difficult than for the control dogs.
3. Impairments in retention and acquisition were more marked, when tested with more difficult tasks.
4. The differential threshold of visual performance was remarkably impaired by ablation of the inferotemporal lobes, but it recovered to the preoperative level after a long period of training. It was, however, not affected by the control operation.
5. The inferotemporal-operated dogs showed some kind of spatial disorientation, while the control dogs did not.
6. The significance of the inferotemporal lobe for visual performance was discussed.