A deficit in ambient visual guidance following superior colliculus lesions in rats

Rats were tested for their ability to locate a hidden platform in the Morris swimming pool in which extrapool cues are required to guide locomotion. At the end of each trial, the rats were either removed immediately or allowed to remain on the platform for 60 s. Bilateral lesions of the superior colliculus (SC), as in a previous experiment (Milner & Lines, 1983), were found to produce a severe deficit. Permitting the rats to stay on the platform did not significantly affect performance in either rats with SC lesions or sham-operated controls. The results indicated that the reduced orienting behavior on the platform observed in the rats with lesions in the previous experiment was not the cause of their navigational impairment. It is concluded that the impairment following SC lesions comes about during the swimming itself and therefore that it may be attributed to a disturbance of, or a failure to utilize, ambient vision.