Private lines of cortical visual information to the nucleus of the optic tract and dorsolateral pontine nucleus.
The subcortical nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN), along with the dorsolateral pontine nucleus (DLPN), has been shown to play a pivotal role in controlling slow eye movements. Both nuclei are known to receive cortical input from striate and extrastriate cortex. To determine to what degree this cortical input arises from the same areas, and potentially from the same individual neurons, in one set of experiments we placed different retrograde tracers into the NOT-DTN and the DLPN. In the ipsilateral cortical hemisphere the two projections mainly overlapped in the middle temporal (MT) area, the middle superior temporal (MST) area, and the visual area in the fundus of the STS (FST) and the surrounding cortex. In these areas, neurons projecting to the NOT-DTN or the DLPN were closely intermingled. Nevertheless, only 3-11% of the labelled neurons in MT and MST were double-labelled in our various cases. In a second set of experiments, we identified neurons in areas MT and MST projecting to the DLPN and/or to the NOT-DTN by antidromic electrical stimulation. Again, 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. 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 indicate that the cortical input to the NOT-DTN and DLPN arises from largely separate neuronal subpopulations in the motion sensitive areas in the posterior STS. Only a small percentage of the projection neurons bifurcate to supply both targets. These findings are discussed in relation to the effects of cortical lesions on the optokinetic and smooth pursuit system.
Distler
Claudia
C
Allgemeine Zoologie & Neurobiologie, Ruhr-Universität Bochum, Bochum, Germany.
Hoffmann
Klaus-Peter
KP
D000818:Animals; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology; D005133:Eye Movements / Q000502:physiology; D000882:Haplorhini; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D011149:Pons / Q000033:anatomy & histology / Q000502:physiology; D014795:Visual Pathways / Q000033:anatomy & histology / Q000502:physiology