Effect of ibotenic acid lesions of the omnipause neurons on saccadic eye movements in rhesus macaques

1. Although much is known about the neurons that control saccadic eye movements, the precise manner in which they interact is still uncertain. To test the validity of competing models of the pontine saccade generator, neurotoxic lesions were made in the nucleus raphe interpositus (rip), which contains one of the principal types of saccade-related neurons, the omnipause neurons (OPNs). The correlated changes in eye movement were quantified in three juvenile rhesus macaques and compared with the results predicted by different models. 2. After the location of the OPNs was mapped, the rip was subjected to sequential, punctate pressure injections of ibotenic acid. The resulting progressive damage was correlated with changes in saccade metrics, including a decrease in peak saccadic velocity and an increase in saccade duration. 3. The damage to rip and presumably to the OPNs was not associated with a change in the animals' ability to maintain steady fixation of a stationary target. 4. The results suggest that Robinson's original local feedback model of saccade generation should be modified. Either a second integrator should be added or the concept of local feedback should be abandoned entirely. 5. The suggestion that the OPNs are primarily responsible for fixation is probably incorrect. OPNs may contribute to fixation stability along with a number of other sources.

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Properties of Horizontal Saccades Accompanied by Blinks

Journal of Neurophysiology ◽

10.1152/jn.1998.79.6.2895 ◽

1998 ◽

Vol 79 (6) ◽

pp. 2895-2902 ◽

Cited By ~ 55

Author(s):

Klaus G. Rottach ◽

Vallabh E. Das ◽

Walter Wohlgemuth ◽

Ari Z. Zivotofsky ◽

R. John Leigh

Keyword(s):

Eye Movements ◽

Peak Velocity ◽

Dynamic Properties ◽

Human Subjects ◽

Saccadic Eye Movements ◽

Stationary Target ◽

Normal Human ◽

The Right ◽

Straight Ahead ◽

Omnipause Neurons

Rottach, Klaus G., Vallabh E. Das, Walter Wohlgemuth, Ari Z. Zivotofsky, and R. John Leigh. Properties of horizontal saccades accompanied by blinks. J. Neurophysiol. 79: 2895–2902, 1998. Using the magnetic search coil technique to record eye and lid movements, we investigated the effect of voluntary blinks on horizontal saccades in five normal human subjects. The main goal of the study was to determine whether changes in the dynamics of saccades with blinks could be accounted for by a superposition of the eye movements induced by blinks as subjects fixated a stationary target and saccadic movements made without a blink. First, subjects made voluntary blinks as they fixed on stationary targets located straight ahead or 20° to the right or left. They then made saccades between two continuously visible targets 20 or 40° apart, while either attempting not to blink, or voluntarily blinking, with each saccade. During fixation of a target located straight ahead, blinks induced brief downward and nasalward deflections of eye position. When subjects looked at targets located at right or left 20°, similar initial movements were made by four of the subjects, but the amplitude of the adducted eye was reduced by 65% and was followed by a larger temporalward movement. Blinks caused substantial changes in the dynamic properties of saccades. For 20° saccades made with blinks, peak velocity and peak acceleration were decreased by ∼20% in all subjects compared with saccades made without blinks. Blinks caused the duration of 20° saccades to increase, on average, by 36%. On the other hand, blinks had only small effects on the gain of saccades. Blinks had little influence on the relative velocities of centrifugal versus centripetal saccades, and abducting versus adducting saccades. Three of five subjects showed a significantly increased incidence of dynamic overshoot in saccades accompanied by blinks, especially for 20° movements. Taken with other evidence, this finding suggests that saccadic omnipause neurons are inhibited by blinks, which have longer duration than the saccades that company them. In conclusion, the changes in dynamic properties of saccades brought about by blinks cannot be accounted for simply by a summation of gaze perturbations produced by blinks during fixation and saccadic eye movements made without blinks. Our findings, especially the appearance of dynamic overshoots, suggest that blinks affect the central programming of saccades. These effects of blinks need to be taken into account during studies of the dynamic properties of saccades.

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Natural and drug-induced variations of velocity and duration of human saccadic eye movements: Evidence for a control of the neural pulse generator by local feedback

Biological Cybernetics ◽

10.1007/bf00336734 ◽

1981 ◽

Vol 39 (2) ◽

pp. 87-96 ◽

Cited By ~ 235

Author(s):

R. J�rgens ◽

W. Becker ◽

H. H. Kornhuber

Keyword(s):

Eye Movements ◽

Pulse Generator ◽

Saccadic Eye Movements ◽

Drug Induced ◽

Local Feedback

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Residual Vision in Multiple Retinal Locations within a Scotoma: Implications for Blindsight

Journal of Cognitive Neuroscience ◽

10.1162/jocn.1997.9.2.191 ◽

1997 ◽

Vol 9 (2) ◽

pp. 191-202 ◽

Cited By ~ 41

Author(s):

R. W. Kentridge ◽

C. A. Heywood ◽

L. Weiskrantz

Keyword(s):

Eye Movements ◽

Visual Field ◽

Stimulus Display ◽

Discrimination Performance ◽

Saccadic Eye Movements ◽

Lower Visual Field ◽

Eye Tracker ◽

Residual Vision ◽

Fixation Stability ◽

The Subject

There is an important new proposal that “blindsight”-the ability to detect and identify visual stimuli by forcedchoice guessing and in the absence of conscious awareness when they fall in blind regions of the visual field—is a function of residual “islands” of undamaged visual cortex. This stands in contrast to the widely accepted view that blindsight is exclusively a function of secondary visual pathways. According to the new view, residual vision in blindsight should be patchy. Thus, when apparently wide areas of residual vision in blindsight are found, these may be due to eye-movements that allow stimuli to pass over retinal locations corresponding to islands of sparing. We tested this hypothesis by examining the distribution of residual vision in blindsight when the effects of eye movements on the retinal location of stimuli were minimized. We report a series of experiments that examined twealternate forcedchoice discrimination in the blind field of the subject GY. Using a dual-Purkinje image eye-tracker we applied three methods of minimizing the effects of retinal slippage due to eye-movements on discrimination performance: fixation stability-dependent trials, software image stabilization, and post hoc rejection of trials in which saccadic eye-movements were detected. In the first experiment, GY's discrimination performance was significantly above chance in 8 of 15 locations tested. In the subsequent experiments the subject knew the location of the target in each block of trials, and this resulted in improvements to performance in a further three locations. Increasing the luminance of the stimulus display (while maintaining 95% target contrast), and increasing the temporal discriminability of the forced choice produced performance above chance in all but two of the locations tested. The consistent chance performance observed in two locations in the lower visual field nevertheless implies that GY's blindsight does not extend over the whole of his scotoma. Nevertheless, abolishing, or minimizing, the effects of eye-movements did not result in a loss of detection in all the widely separated regions tested, and we thus conclude that GY's blindsight cannot adequately be explained in terms of islands of spared vision. Islands may account for residual vision in scotomata in some patients, but cannot be a universal account of the phenomenon of blindsight.

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Mislocalisation of Chromatic and Achromatic Stimuli during Saccadic Eye Movements

Perception ◽

10.1068/v96l0302 ◽

1996 ◽

Vol 25 (1_suppl) ◽

pp. 137-137

Author(s):

M Sato ◽

K Uchikawa

Keyword(s):

Eye Movements ◽

Opposite Direction ◽

Visual Target ◽

Saccadic Eye Movements ◽

Eye Position ◽

Stationary Target ◽

Actual Position ◽

Chromatic Stimulus ◽

Position Signal ◽

Retinal Information

It is well known that a brief flash of a small stationary target presented during saccades appears to be shifted from the actual position. The perceptual location of a visual target should be determined by the retinal information and the eye position signal. This mislocalisation seems to indicate that the change of the eye position signal is more sluggish than the actual eye movements. Delay of transmission of the retinal information may be a factor of mislocalisation. Here, we measured the perceptual location of chromatic stimuli which had different temporal characteristics from achromatic stimuli. The chromatic stimulus was a small red spot which replaced the green field for 10 ms. The green field subtended 5 deg × 24 deg and its luminance was 78.6 cd m−2. The luminance of the chromatic stimulus was adjusted to be the same as the green field by the minimum flicker method. The luminance of the achromatic stimulus was 234 cd m−2. Our results show that the chromatic and the achromatic stimuli presented at the beginning of saccades are mislocalised in the same direction as the saccades. We also found that the mislocalisation of the chromatic stimulus began slightly earlier than the achromatic stimulus. Also the chromatic stimulus presented during saccades was mislocalised in the opposite direction to the saccades whereas the achromatic stimulus was localised approximately at the actual position. These results suggest that the chromatic response is transmitted more slowly before saccades but faster during saccades than the achromatic response.

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Macaque Pontine Omnipause Neurons Play No Direct Role in the Generation of Eye Blinks

Journal of Neurophysiology ◽

10.1152/jn.01150.2009 ◽

2010 ◽

Vol 103 (4) ◽

pp. 2255-2274 ◽

Cited By ~ 12

Author(s):

K. P. Schultz ◽

C. R. Williams ◽

C. Busettini

Keyword(s):

Eye Movements ◽

Eye Movement ◽

Time Constant ◽

Dynamic Change ◽

Saccadic Eye Movements ◽

Oscillatory Behavior ◽

Saccadic Eye Movement ◽

Direct Role ◽

Eye Blinks ◽

Omnipause Neurons

We recorded the activity of pontine omnipause neurons (OPNs) in two macaques during saccadic eye movements and blinks. As previously reported, we found that OPNs fire tonically during fixation and pause about 15 ms before a saccadic eye movement. In contrast, for blinks elicited by air puffs, the OPNs paused <2 ms before the onset of the blink. Thus the burst in the agonist orbicularis oculi motoneurons (OOMNs) and the pause in the antagonist levator palpabrae superioris motoneurons (LPSMNs) necessarily precede the OPN pause. For spontaneous blinks there was no correlation between blink and pause onsets. In addition, the OPN pause continued for 40–60 ms after the time of the maximum downward closing of the eyelids, which occurs around the end of the OOMN burst of firing. LPSMN activity is not responsible for terminating the OPN pause because OPN resumption was very rapid, whereas the resumption of LPSMN firing during the reopening phase is gradual. OPN pause onset does not directly control blink onset, nor does pause offset control or encode the transition between the end of the OOMN firing and the resumption of the LPSMNs. The onset of the blink-related eye transients preceded both blink and OPN pause onsets. Therefore they initiated while the saccadic short-lead burst neurons were still fully inhibited by the OPNs and cannot be saccadic in origin. The abrupt dynamic change of the vertical eye transients from an oscillatory behavior to a single time constant exponential drift predicted the resumption of the OPNs.

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