Private lines of cortical visual information to the nucleus of the optic tract and dorsolateral pontine
nucleus
C. Distler & K.-P. Hoffmann
Prog.Brain Res.171:363-368, 2008
- 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.
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