Suppression of trans-geniculate transmission during the rapid phase of caloric nystagmus in the alert squirrel monkey

Sustained and transient discharges of retinal ganglion cells during spontaneous eye movements of cat

Discharges of 223 retinal ganglion cells during spontaneous eye movements (saccades) across a stationary grating pattern were studied in chronically prepared cats. Of these 83 showed sustained responses to local differences in luminance of the grating stripes (S-units); 84 showed transient responses to saccades and did not register local differences in luminance (T-units); and 56 showed mixed responses, i.e., transient responses to saccades and sustained firings in response to local luminance (M-units). When tested with diffuse light, 93.9% of the S-units showed either ON-sustained or OFF-sustained responses; 95.2% of the T-units showed either ON-transient, OFF-transient, or ON-OFF-transient responses; and 50% of the M-units showed ON-OFF responses. In the overall responses properties, most S-units corresponded to the X-cells, most T-units to the Y-cells of retinal ganglion cells previously known from acute experiments. Under normal conditions of active eye movements, the major function of the S-units would be to register the differences in luminance in their receptive fields, and subserve the mechansim of form recognition. The major function of the T-units would be to register information related to quick image motion, induced either by eye or object movements, and subserve the mechanism of detecting the dynamic aspects of visual stimuli. The other important functions of the T-units are their possible participation in the afferent routes for two recently proposed mechanisms; one for goal-directed saccades and the other for saccadic suppression. The M-units would possess the functions of both S- and T-units.

Influence of eye movements on geniculo-striate excitability in the cat

1. The excitability of the geniculo-striate pathway during a saccadic eye movement was studied in alert cats with chronically implanted electrodes. Excitability was assessed by the amplitude of post-synaptic components of field responses in both lateral geniculate nucleus and visual cortex to electrical stimulation of the optic chiasm. Modifications in amplitude were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in the electrooculograms and altering delays in the stimulus pulse.2. The post-synaptic component of the geniculate response was markedly depressed for about 150 msec, reaching a trough at approximately 100 msec after the initiation of an eye movement. This effect was dependent on the visual environment and was not observed in complete darkness. A similar depression occurred when the visual field was abruptly moved by retinal impulses generated by a quick displacement of the image of the visual world associated with an eye movement. The depression reflected a reduction of cellular discharge to the orthodromic volley and hence a suppression of the transmission of visual information through the lateral geniculate nucleus. This may be a mechanism for saccadic suppression.3. The post-synaptic components of the cortical response were enhanced for about 200 msec, reaching a peak at approximately 150 msec after the initiation of an eye movement. Although this facilitation occurred also in complete darkness, it did not occur when the visual field was abruptly shifted while the eyes were stationary. The fact that it occurred with eye movements and exclusively in the post-synaptic components suggests that it was caused by signals from a system closely related to eye movements. This may be a manifestation of the corollary mechanism.