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Biomedical subjects

S M Blair

Publications and source records attributed to S M Blair.

At least 19 recordsLinked to original sources
PubMed1981

The effect of habituating vestibular and optokinetic nystagmus on each other.

Currently, the vestibulo-ocular and optokinetic reflexes are both thought to require a velocity storage mechanism within their neural pathways. To test whether these storage mechanisms are shared by both reflexes, animals were given programs of stimulation known to change the status of the storage mechanism of one of the type of nystagmus. The other type of nystagmus was examined then to ascertain whether the characteristic of its velocity storage system had remained invariant. Horizontal eye movements of three macaque monkeys were recorded during post-rotatory nystagmus and optokinetic afternystagmus (OKAN) before and after 20 habituating exposures to either vestibular or optokinetic stimulation. Repetitive exposures to vestibular stimulation alone markedly reduced the time constant of post-rotatory nystagmus and this effect was accompanied only occasionally by a reduction in the time constant of OKAN. Repetitive exposure to optokinetic stimulation alone reliably reduced the time constant of OKAN but produced no reliable change in the time constant of post-rotatory nystagmus. These results suggest that the vestibulo-ocular and optokinetic reflexes do not share a single common velocity storage mechanism.

Animals↗
PubMed1980

Expression of cupular dynamics while the macaque sleeps.

(1) The effect of brief periods of sleep on neural processing in the vestibulo-ocular reflex was studied in Macaca speciosa. (2) When sleep interrupted nystagmus during a modified Bárány spinning test, the time constant of mystagmus remained unchanged. (3) This finding shows that during light sleep the neural circuitry which generates a long nystagmus time constant from a short cupular time constant continues to function, even though nystagmus ceases.

Animals↗
PubMed1979

Modifications of vestibulo-ocular reflex induced by diazepam: experiments in the macaque.

The vestibulo-ocular reflex in the macaque was tested before and after intravenous administration of diazepam. The drug effect was marked by decrease in gain and increase in time constant of nystagmus in response to a modified Bárány test and by reduction in directional asymmetry of nystagmus. Because the time course of reduction in gain differed from the time course of increase in time constant, diazepam probably has more than one site of action. These results emphasize the complexity of neural processing in the vestibulo-ocular reflex arc.

Animals↗
PubMed1978

Neural pathways common to vestibular and optokinetic eye movements.

To determine how vestibular and optokinetic eye movement signals share the central oculomotor neural organization, optokinetic afternystagmus was superposed on vestibular nystagmus in the monkey. To a first approximation there was algebraic additivity in the velocity domain. This result suggests that vestibular and optokinetic eye movements are integrated at a level of neural organization above the ocular motoneurons, at a level in which neural signals are coded in terms of eye movement velocity rather than eye position.

Animals↗
PubMed1975

[Synkinesis of head and eye movements evoked by brainstem stimulation in the alert monkey].

The synkinesis of head and eye movements evoked by electrical stimulation of the tectum and tegmentum in the alert monkey is described. In positions where both head and eye movements can be evoked, the two are almost always parallel in direction and they are superimposed on rather than substituted for each other. The directiion of movement depends on the stimulated positions: tilt and turn reactions are distributed according to laterality, direction of vertical movements depends more on the stimulus parameter than the electrode position. Head movements release vestibulo-ocular reflexes, which are superimposed on the electrically evoked eye movements.

Animals↗
PubMed1975

The ocular tilt reaction--a brainstem oculomotor routine.

Electrical stimulation of brainstem tegmentum in alert macaques elicits a stereotyped ocular movement routine characterized by vertical divergence and conjugate cycloversion. The movement pattern is similar to those seen in the clinical syndromes of see-saw nystagmus and skew deviation. The stimulated movement pattern is not dependent on initial eye position and cannot be produced when the animal is under barbiturate anesthesia. It is not overridden by saccadic inhibition stimulation and is present in cerebellectomized and labyrinthectomized monkeys.

Animals↗