The time course of barbiturate action in man investigated by measurement of smooth tracking eye movement

Use of simple tasks to test for impairment of complex skills by a sedative

Examination of the effect of three doses of pentobarbital on the comparative performance of a complex psychomotor task with two simple neuromotor tasks, i. e., standing steady and pendulum eye tracking, revealed a high correlation. These simple tasks could be used as measures of intoxication since they do not require extensive training. Examination of the complex task impairment blood level ratio revealed that impairment relative to blood level was much greater in the absorption phase. This changing ratio underscores the point that blood levels alone are not an adequate estimate of intoxication.

Smooth pursuit eye movements of normal and schizophrenic subjects tracking an unpredictable target

An experimental paradigm employed by several workers in the field of schizophrenic eye movements has involved finding sequences of stimuli that induce saccadic smooth pursuit in the eye movements of normal individuals. It is hoped that the identification of such stimuli will lead to clues concerning the etiology or nature of eye tracking dysfunction in schizophrenia. In this study, the pursuit eye movements of normal and schizophrenic subjects tracking an unpredictable target (composed of summed sine waves) were examined. Eye tracking performance was evaluated both qualitatively and quantitatively using percent root-mean-square (%RMS) error and pursuit gain scores. Schizophrenics are capable of tracking an unpredictable target. This finding has implications for our understanding of schizophrenic information processing during visual tracking.

The effects of ethanol on eye tracking in rhesus monkeys and humans

The effects of ethanol on eye tracking function were compared in rhesus monkeys and humans using a similar experimental procedure. In Experiment 1, 3 rhesus monkeys were trained to visually track a projected image of a disk that oscillated sinusoidally along a horizontal plane on a screen. This training was accomplished using a procedure in which responses on a lever resulted in the delivery of water when the central area of the projected disk image was dimmed for a brief period. Intragastric administrations of ethanol at doses of 0.25 to 2 g/kg were tested during one-day test sessions using a cumulative dose procedure. Pursuit eye movements were disrupted at doses of 0.5 g/kg while lever pressing behavior was not disrupted until a dose of 2 g/kg was reached. In Experiment 2, pursuit eye movements of 6 humans were not disrupted when ethanol was given orally at cumulative doses of 0.25 to 1 g/kg, while microswitch pressing behavior was disrupted in some of the subjects at a dose of 0.5 g/kg. Blood ethanol levels increased in a dose-dependent manner in both species with higher levels in humans than in monkeys. The dose dependent effects observed in both species and qualitative similarities in some of the effects such as saccadic pursuit eye movements suggest that the eye tracking method employing monkeys is useful for predicting drug effects on sensory motor function in humans.

Study of pursuit and vestibulo-ocular cancellation

This present study, a follow-up of our earlier investigation, further examines the time courses of recovery of oculomotor and vestibular function while patients are under the sedative effect of a single dose of secobarbital (Seconal). The assessment included tests for saccade and smooth pursuit, and the vestibulo-ocular reflex and its cancellation, as evaluated by sinusoidal and pseudorandom rotation in a high-frequency hydraulic chair (up to 5 Hz). Analysis of results showed that the vestibulo-ocular reflex (VOR) gain, depressed soon after drug intake, recovered substantially after a few hours. Changes in VOR gain were more pronounced with higher frequencies of rotation at 2 and 3 Hz, and greater with pseudorandom than sinusoidal stimulation. Under barbiturate influence, pursuit and VOR cancellation followed distinctly different time courses of recovery. This dissociation between VOR cancellation and pursuit supports the theory that these two systems are subserved by different mechanisms. Saccadic hypermetria was also observed after drug intake.

Effects of dopaminergic agents on eye tracking before and after repeated methamphetamine

The effects of methamphetamine (MA), apomorphine (AP) and haloperidol (HAL) on eye tracking function were tested in rhesus monkeys. Three rhesus monkeys were trained to track with their eyes a disk-shaped projected image that oscillated along a horizontal plane on a screen, using a training procedure in which responses on a lever were reinforced with water only when the center of the disk dimmed for a brief period. Eye movements were recorded by electrooculography (EOG). The effects of intramusuclar administration of MA, APO and HAL on responding were compared before and after a 8-14 day period of repeated MA administration. During this regimen, MA was given in 4 divided doses starting at a total daily dose of 4 mg/kg/day and increasing to 16-40 mg/kg/day. All three drugs disrupted performance during both the initial dose-response determination as well as during the redetermination following the regimen. However, tolerance to MA in 3 monkeys and to APO in 2 monkeys was observed after the regimen, while no marked sensitivity change was observed to haloperidol. Since other data reported elsewhere have shown that dopamine is depleted in the caudate after similar repeated administration regimens, long lasting brain dopaminergic changes are likely present in these monkeys. Therefore, these results suggest that the changes in sensitivity to the drugs that were observed in terms of eye tracking function are related to dopamine depletion in the brain.

Effects of phencyclidine, secobarbital and diazepam on eye tracking in rhesus monkeys

Rhesus monkeys were trained to track a moving disk using a procedure in which responses on a lever were reinforced with water delivery only when the disk, oscillating in a horizontal plane on a screen at a frequency of 0.4 Hz in a visual angle of 20 degrees, dimmed for a brief period. Pursuit eye movements were recorded by electrooculography (EOG). IM phencyclidine, secobarbital, and diazepam injections decreased the number of reinforced lever presses in a dose-related manner. Both secobarbital and diazepam produced episodic jerky-pursuit eye movements, while phencyclidine had no consistent effects on eye movements. Lever pressing was disrupted at doses which had little effect on the quality of smooth-pursuit eye movements in some monkeys. This separation was particularly pronounced with diazepam. The similarities of the drug effects on smooth-pursuit eye movements between the present study and human studies indicate that the present method using rhesus monkeys may be useful for predicting drug effects on eye tracking and oculomotor function in humans.

Determination of smooth pursuit eye movement velocity in humans by computer

Smooth pursuit eye movements are the output of a system closely related to visual suppression of the vestibulo-ocular reflex, and impairment of these functions when performing day-to-day activities may be important. Smooth pursuit velocity has been assessed using a computerized electro-oculographic technique based on the amount of saccadic activity detected throughout a range of visual target velocities spanning the capability of the smooth pursuit system. Each test session lasts 2 min. With this technique the effects on smooth pursuit of various centrally acting compounds have been demonstrated in healthy subjects. Healthy females had lower smooth pursuit velocities when compared to age-matched males. A linear correlation was shown between smooth pursuit velocity determined by the computer technique and by a previously reported visual method. Such measures have wide application in neurological diagnosis and in the assessment of the central effects of drugs in man.

Smooth-pursuit eye movements, and diazepam, CPZ, and secobarbital

This study examined the effects on smooth-pursuit eye tracking of single doses of CPZ (0.667 and 1.334 mg/kg), diazepam (0.071, 0.142, and 0.284 mg/kg), and secobarbital (100 mg). Only the barbiturate significantly affected the ability to follow a moving target with smooth-pursuit eye movements. In repeated testing of a single subject, 130 mg of secobarbital disrupted smooth-pursuit movements at least until 24 hrs after ingestion.