The rat accessory optic system: effects of cortical lesions on the directional selectivity of units within the medial terminal nucleus.

Single units within the medial terminal nucleus of the accessory optic system were recorded and examined for their responses to a moving pattern, in both intact and decorticated urethane-anesthetized rats. The preferred directions of motion in control rats were mainly upward with a temporal component and downward with a nasal component. The responses to upward motion were almost absent after cortical ablation, with most units now preferring temporal or downward-nasal directions. These data suggest that cortical structures modulate the directional selectivity of accessory optic neurons in the rat.