Visual response properties of neurons in cortical areas MT and MST projecting to the dorsolateral pontine nucleus or the nucleus of the optic tract in macaque monkeys

Abstract

Neurons in cortical medial temporal area (MT) and medial superior temporal area (MST) projecting to the dorsolateral pontine nucleus (DLPN) and/or to the nucleus of the optic tract and dorsal terminal nucleus (NOT-DTN) were identified by antidromic electrical stimulation in five macaque monkeys. Neurons projecting to either target were located in close proximity to each other, and in all subregions of MT and MST sampled. Only a small percentage of the antidromically identified projection neurons (4.4%) sent branches to both the NOT-DTN and the DLPN. Antidromic latencies of neurons projecting to the NOT-DTN (0.9-6 ms, median 2.1 ms) and to the DLPN (0.8-5 ms, median 2.0 ms) did not differ significantly. Visual response properties of the neurons antidromically activated from either site did not differ significantly from those of cells that were not so activated. On the population level only neurons activated from the NOT-DTN had a clear preference for ipsiversive stimulus movement, whereas the neurons activated from the DLPN and neurons not antidromically activated from either target had no common directional preference. These results are discussed in terms of specification of cortico-subcortical connections and with regard to pathways underlying slow eye movements in different visuomotor behaviours.