Distractibility following simultaneous bilateral lesions of the superior colliculus or medial frontal cortex in the rat.

Hooded rats with bilateral lesions of the superior colliculus or medial frontal cortex were compared with controls for locomotor guidance in shuttling back and forth between goal-doors at two opposite ends of a large arena. Colliculectomized rats accomplished this with great accuracy. When flashing distractor lights were introduced midway down the runway, frontal corticals and controls were severely disrupted but colliculars continued to run normally. This result was obtained both when all training occurred postoperatively (Experiment 1) and when runway performance had been stabilized preoperatively (Experiment 2), thus after a long or short postoperative recovery interval. The results offer support for previous studies with rats which have demonstrated sensory 'neglect' but good locomotor guidance after collicular ablation. Frontal corticals differed from controls only in terms of their elevated rate of repeat door-pressing upon postoperative resumption of testing in Experiment 2. Despite the similarity between effects reported elsewhere of collicular and frontal lesions made unilaterally, bilateral deficits clearly demonstrable after collicular ablation were absent here after frontal lesions. The results imply that the functional responsibilities of superior colliculus and frontal cortex in the rat are separable; at least, they have different rates of functional recovery.