In subjects suffering from early onset stra- bismus, signals conveyed by the two eyes are not perceived simultaneously but in alternation. We exploited this phenom- enon of interocular suppression to investigate the neuronal correlate of binocular rivalry in primary visual cortex of awake strabismic cats. Monocularly presented stimuli that were readily perceived by the animal evoked synchronized discharges with an oscillatory patterning in the g-frequency range. Upon dichoptic stimulation, neurons responding to the stimulus that continued to be perceived increased the syn- chronicity and the regularity of their oscillatory patterning while the reverse was true for neurons responding to the stimulus that was no longer perceived. These differential changes were not associated with modifications of discharge rate, suggesting that at early stages of visual processing the degree of synchronicity rather than the amplitude of responses determines which signals are perceived and control behav- ioral responses.

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Synchronization of oscillatory responses in visual cortex correlates with perception in interocular rivalry

Spike and local field potential activity were recorded simultaneously from multiple sites in primary visual cortex of strabismic cats, while monocular stimulation alternated with dichoptic stimulation, inducing interocular rivalry. During interocular rivalry, there is competition between the two nonfusible stimuli presented to the two eyes, and only one stimulus is selected at any time. We biased this competition in three different ways: (1) we exploited the condition that in strabismic cats there is often one dominant eye that is selected for most of the time. (2) We presented the two stimuli with a temporal offset, which biases competition in favor of the newly appearing stimulus. (3) We presented the two stimuli with highly different contrasts, which biases competition in favor of the stimulus with higher contrast. Whenever competition was biased in favor of the stimulus activating the recorded neurons, gamma-frequency synchronization of the respective responses was enhanced, and vice versa. Firing rates showed some differences between stimulation conditions. However, when present, these changes were inversely related to a competitive advantage of the respective stimulus. We hypothesize that enhanced gamma-frequency synchronization in primary visual cortex is a correlate of stimulus selection. Synchronization is likely to be translated into firing rate changes at later processing stages.

https://www.jneurosci.org/content/jneuro/22/9/3739.full.pdf

Oscillatory neuronal synchronization in primary visual cortex as a correlate of stimulus selection

The effects of bilateral electrolytic lesions within and around the prepositus hypoglossi (ph) nucleus on horizontal saccades in the dark and on the horizontal sinusoidal vestibulo-ocular reflex (vor) in the dark were studied After ph lesion, including its rostral part between P 7 and P 8, the vor showed a phase lead as much as about 90 deg at 010 Hz A significant gain reduction paralleled that phase lead at lower frequencies A large post-saccadic drift was also observed, the time constant of which ranged from 03 to 06 s After ph lesion extending from P 8 to P 11 (but sparing the rostral part of the ph), no significant gain or phase lead change was observed Post-saccadic drift was either missing or weak A bilateral medial vestibular nucleus (mvn) lesion from P 7 to P 11 produced a marked gain decrease, paralleled by a marked phase advance A post-saccadic drift was observed (tau = 06 s) A surgical mid-line lesion from P 7 to P 11 (depth: about 2 mm) was followed by no remarkable change in the gain and in the phase of the vor No post-saccadic drift was observed after such lesion It was concluded that (i) both the horizontal vor integration processing, and the horizontal saccadic integration processing were destroyed when an electrolytic lesion was made 'in the region of' the rostral part of the ph nucleus, and that (ii) the posterior four-fifths of the ph was the location of neither the horizontal vor integrator nor the horizontal saccadic integrator

Lesions in the cat prepositus complex: effects on the vestibulo-ocular reflex and saccades

In the present study the optokinetic reflex, vestibulo-ocular reflex and their interaction were investigated in the mouse, using a modified subconjunctival search coil technique. Gain of the ocular response to sinusoidal optokinetic stimulation was relatively constant for peak velocities lower than 88 / s, ranging from 0.7 to 0.8. Gain decreased proportionally to velocity for faster stimuli. The vestibulo-ocular reflex acted to produce a sinusoidal compensatory eye movement in response to sinusoidal stimuli. The phase of the eye movement with respect to head movement advanced as stimulus frequency decreased, the familiar signature of the torsion pendulum behavior of the semicircular canals. The first-order time constant of the vestibulo-ocular reflex, as measured from the eye velocity decay after a vestibular velocity step, was 660 ms. The response of the vestibulo-ocular reflex changed with stimulus amplitude, having a higher gain and smaller phase lead when stimulus amplitude was increased. As a result of this nonlinear behavior, reflex gain correlated strongly with stimulus acceleration over the 0.1‐1.6 Hz frequency range. When whole body rotation was performed in the light the optokinetic and vestibular system combined to generate nearly constant response gain (approximately 0.8) and phase (approximately 08) over the tested frequency range of 0.1‐1.6 Hz. We conclude that the compensatory eye movements of the mouse are similar to those found in other afoveate mammals, but there are also significant differences, namely shorter apparent time constants of the angular VOR and stronger nonlinearities. © 2001 Elsevier Science B.V. All rights reserved.

Research report The dynamic characteristics of the mouse horizontal vestibulo-ocular and optokinetic response

https://repub.eur.nl/pub/73429/1-s2.0-S0006899300031802-main.pdf

Jean Halleux

Papers

Vestibuloocular reflex, optokinetic response, and their interactions in the alert cat