Orienting behavior in hamsters with lesions of superior colliculus, pretectum, and visual cortex.

We examined cortical and subcortical mediation of visual locomotor orienting function by comparing the behavior of hamsters with discrete bilateral lesions affecting the pretectum, superior colliculus (SC), or visual cortex (VC). Orienting and approach to stationary targets was evaluated by measuring the accuracy of hamsters' approaches to small black apertures, located at eye level along the wall of a circular white arena. Hamsters with bilateral ablation of the visual cortex were slightly impaired for approaches to central field targets, whereas those with ibotenic acid lesions of the pretectum (which spares fibers of passage and thus leaves tectal afferents intact) were totally unimpaired. Hamsters with transection of the brachium of SC (BSC) at the prectectal-SC (PT-SC) border were severely impaired in their ability to approach stationary targets in central and peripheral fields. Thus, we did not detect any of the central field sparing that has been reported by others for rodents with similar lesions. Several possible reasons for the disparity between our results and those of others are discussed. Overall, our results indicate that in hamsters the SC is essential for normal visually guided approach to dark, stationary targets throughout the visual field. Further, our results and qualitative observations indicate that the approach errors are most likely due to deficits of visuomotor integration rather than to a lack of visual scanning.