VISUAL RESPONSES OF NEURONS FROM AREAS V1 AND MT IN A MONKEY WITH LATE-ONSET STRABISMUS - A CASE-STUDY

One adult monkey (Macaca fascicularis) was investigated psychophysical ly and electrophysiologically after at least 5 years of late onset eso tropic macrostrabismus (squint angle 52 deg). Behavioural tests reveal ed normal monocular visual and visuomotor functions. No indications of deep amblyopia or oculomotor asymmetry were found. The monkey used th e left or right eye alternately at about equal frequencies. Single uni t recordings from area V1 disclosed a normal ocular dominance distribu tion. Most V1 neurons from both hemispheres received binocular input. Thus, discordant visual information from corresponding retinal locatio ns of the two eyes converged onto the cortical neurons. No evidence fo r anomalous retinal correspondence was found. Diplopia and confusion m ust therefore be avoided by suppression of vision through one eye to a llow stable, unambiguous perception. Possible suppression was investig ated by stimulating a neuron through the same eye when it was actively used for fixation in one set of trials, and when it was not used for fixation in another set of trials. Significant differences in these tw o stimulus conditions were found in 20/39 neurons from area V1 and in 11/34 motion sensitive neurons recorded in the middle superior tempora l area (MT). The normalized population activity in V1 and MT was highe r if cells were stimulated through the fixating eye. The data are disc ussed with respect to possible suppressive mechanisms helping to preve nt double vision in strabismus and in binocular rivalry. (C) 1997 Else vier Science Ltd. All rights reserved.