Effects of serial unilateral and serial bilateral visual cortex lesions on brightness discrimination relearning in rats.

In Experiment 1, rats with serial unilateral (SU), serial bilateral (SB), or one-stage bilateral (B) visual cortex lesions (areas 17, 18 and 18a) were compared in their retention of a preoperatively learned brightness discrimination. Both the first-stage and second-stage lesions for the SU and SB groups involved the same amount of cortical tissue and the same composite areas of visual field projection in primary and extraprimary visual cortex. Groups SU and SB showed substantial savings of the brightness discrimination after the completed bilateral visual cortex removals, while Group B showed a complete postoperative loss. In Experiment 2, the effects of two additional types of serial bilateral visual cortex lesions were investigated. These involved the medial and then lateral aspects of visual cortex in two stages (ML), or vice versa (LM). Once again, the serial bilateral lesion groups (SB, ML, and LM) showed substantial savings of the discrimination after the completed lesion, while Group B showed a complete post-operative loss. These results demonstrate a general advantage of serial damage over one-stage damage to visual cortex in recovery of a preoperatively learned brightness discrimination and indicate that the serial lesion effect is not specific to interhemispheric relationships.