Cortical input to the nucleus of the optic tract and dorsal terminal nucleus (NOT-DTN) in macaques: a retrograde tracing study.

Using retrograde tracing methods, we investigated the cortical projection to the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) in macaque monkeys. Tracer injections at electrophysiologically identified recording sites in the NOT-DTN resulted in retrogradely labelled neurons in layer V of various cortical areas. The strongest projection always arose from the middle temporal area (MT) and the adjoining cortex anterior to MT in the superior temporal sulcus. A less dense projection came from the middle superior temporal area (MST). In addition, retrogradely labelled cells were consistently found in areas V1 and V2 at moderate to high density. Furthermore, sparse to moderate labelling occurred in prestriate area V3. These findings were compared with the label resulting from control injections into the superior colliculus in two additional cases. Our results indicate that the cortical input to the NOT-DTN as the sensorimotor interface for the pathway subserving stabilizing eye movements during the optokinetic reflex and smooth pursuit mainly arises from the motion-sensitive areas MT and MST in the superior temporal sulcus, as well as from areas V1 and V2. Clearly the projection to the NOT-DTN does not arise from a single cortical area.