Response properties of MT neurons in amblyopic macaques

El-Shamayleh, Yasmine, Kohn, Adam, Movshon, J Anthony and Kiorpes, Lynne.

Published in Journal of Vision, vol.7(9), pp. 392--392, 2007.
Cells in area MT/V5 are selective for motion direction, speed, and some correctly signal the motion of complex patterns. We have studied the responses of these neurons in monkeys with known deficits in motion perception. We recorded 198 neurons from 3 amblyopic macaques (2 strabismics, 1 anisometrope) whose behavioral sensitivity to coherent motion in random dot displays was reduced at fine spatial offsets and long temporal offsets when tested in the amblyopic eye (Kiorpes et al, 2006, Vis. Neurosci.).

We studied neurons driven by both eyes in both hemispheres. Many neurons could be activated through either eye, but we found a clear shift in eye dominance away from the amblyopic eyes. We measured selectivity for grating direction, spatial and temporal frequency, and for pattern motion using plaids. We also measured selectivity for dot direction, speed, displacement, temporal offset, and sensitivity to motion coherence. We found no differences between the selectivity of neurons driven by the fellow and amblyopic eyes. We used a pooling method to analyze neuronal coherence sensitivity, and found no difference in any animal between pools of neurons driven by the two eyes. For both eyes, behavioral sensitivity to coherent motion was much better than neuronal sensitivity at long temporal offsets, suggesting that areas other than MT — perhaps downstream of MT — are responsible for integrating coherent motion information over time.

We conclude that changes in the properties of MT neurons are not responsible for the behavioral motion deficits of these amblyopic subjects.Our results suggest that the effects of amblyopia on motion processing occur in areas downstream of MT

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