Head-dipping in rats with superior collicular, medial frontal cortical and hippocampal lesions

When tested in a modified "holeboard" apparatus, hooded rats with deep superior collicular lesions were hyperactive, reared less than controls and spent a great deal of time at the apparatus perimeter. They failed to explore holes in the floor and frequently fell into them. Those with lesions restricted to superficial laminae showed reduced rearing, and preference for the perimeter but were normally active and explored floor holes as frequently as controls. The frontal cortical group failed to differ from controls on any measure. Hippocampals exhibited reduced intersession habituation of locomotor activity. It was concluded that superior colliculus, hippocampus and medial frontal cortex have separate functional roles. Differences between deep and superficial collicular lesion effects might arise because deep lesions disrupt both motor integration and attention while superficial lesions disrupt only the latter. Alternatively, since superficial lesions spare lateral tissue subserving attention to stimuli in lower portions of the visual field, they may produce a less global attentional deficiency which has less impact upon motor function.