Smooth pursuit eye movements: effects of alcohol and chloral hydrate

Alcohol impairment of saccadic and smooth pursuit eye movements: impact of risk factors for alcohol dependence

RATIONALE

While persons at risk for alcohol dependence by virtue of heavy drinking patterns or family history (FH) of alcohol use disorders have exhibited differential alcohol responses on a variety of measures, few studies have examined alcohol's effects on eye movements in these subgroups.

OBJECTIVES

The purpose of this study was to (1) conduct a placebo-controlled, dose-ranging study of alcohol's effects on eye movements and (2) examine the impact of these risk factors on oculomotor response to alcohol.

METHODS

A within-subject, double-blind laboratory study was conducted in N = 138 heavy (HD; n = 78) and light social drinkers (LD; n = 60) with self-reported positive (FH+) or negative (FH-) family history. Subjects participated in three laboratory sessions in which they consumed a beverage containing a high (0.8 g/kg) or low (0.4 g/kg) dose of alcohol or placebo. Smooth pursuit, pro-saccadic, and anti-saccadic eye movements were recorded before and at two intervals after alcohol consumption.

RESULTS

Alcohol significantly impaired smooth pursuit gain and pro- and anti-saccade latency, velocity, and accuracy in a dose and time specific matter. HD and LD showed similar impairment on smooth pursuit gain and anti-saccade measures, but HD were less impaired in pro-saccade latency, velocity, and accuracy. FH+ and FH- subjects were equally impaired in nearly all pro- and anti-saccade measures, but FH+ were less impaired in smooth pursuit gain.

CONCLUSIONS

In sum, alcohol produced systematic impairment on oculomotor functioning, even at a non-intoxicating dose. Furthermore, high- and low-risk drinkers may be vulnerable to select performance deficits relative to eye movement task.

Horizontal gaze nystagmus: a review of vision science and application issues

The Horizontal Gaze Nystagmus (HGN) test is one component of the Standardized Field Sobriety Test battery. This article reviews the literature on smooth pursuit eye movement and gaze nystagmus with a focus on normative responses, the influence of alcohol on these behaviors, and stimulus conditions similar to those used in the HGN sobriety test. Factors such as age, stimulus and background conditions, medical conditions, prescription medications, and psychiatric disorder were found to affect the smooth pursuit phase of HGN. Much less literature is available for gaze nystagmus, but onset of nystagmus may occur in some sober subjects at 45 degrees or less. We conclude that HGN is limited by large variability in the underlying normative behavior, from methods and testing environments that are often poorly controlled, and from a lack of rigorous validation in laboratory settings.

A low-cost interface for control of computer functions by means of eye movements

Human-computer interactions (HCI) have become an important area of research and development in computer science and psychology. Appropriate use of computers could be of primary importance for communication and education of those subjects which could not move, speak, see or hear properly. The aim of our study was to develop a reliable, low-cost and easy-to-use HCI based on electrooculography signal analysis, to allow physically impaired patients to control a computer as assisted communication. Twenty healthy subjects served as volunteers: eye movements were captured by means of four electrodes and a two-channel amplifier. The output signal was then transmitted to an "Analog to Digital" (AD) converter, which digitized the signal of the amplifier at a rate of 500 Hz, before being sent to a laptop. We designed and coded a specific software, which analyzed the input signal to give an interpretation of eye movements. By means of a single ocular movement (up, down, left and right) the subjects were then able to move a cursor over a screen keyboard, passing from one letter to another; a double eye blink was then necessary to select and write the active letter. After a brief training session, all the subjects were able to confidently control the cursor and write words using only ocular movements and blinking. For each subject we presented three series of randomized words: mean time required to enter a single character was about 8.5s, while input errors were very limited (less than 1 per 250 characters). Our results confirm those obtained in previous studies: eye-movement interface can be used to properly control computer functions and to assist communication of movement-impaired patients.

On the trail of the genetics and pathophysiology of schizophrenia

Most of us engaged in mental health research and services have been astounded by the extraordinary advances in the basic sciences, particularly in the life sciences, during the past 50 years, which is a mere instant in the span of the recorded history of science. We have witnessed the following, among many others: The discovery in 1944 by Seymour Kety (Kety and Schmidt 1945, 1948) of a method to measure precisely the circulation of the blood in the brain, which permitted the measurement of a metabolic activity of the brain while performing various behavioral tasks, as is now being done with positron emission tomography (PET). The introduction of the phenothiazines into the treatment of psychosis, which led to the intensive study of neural receptor and transmitter dynamics in major mental illnesses and the role these receptors and transmitters play in behavior (Deniker 1970; Laborit et al. 1952). Watson and Crick's (1953) discovery of the double helix structure of DNA, which led to a revolution in molecular biology and made possible the discovery of the genetic etiology of many diseases, including some severe mental diseases. The continued but increasingly sophisticated study of brain anatomical mapping and localization, aided by new electronic and computer techniques. And I add to this list the precise measurement of cognitive processes and the ability to partition mental functions like attention into finer units (cf. Posner 1978).

Eye movements in recovering substance abusers: a prospective study

Smooth-pursuit (SPEM) and saccadic (SEM) eye movements were studied in 11 cocaine-dependent and 4 alcohol-dependent patients after 1, 3, and 12 weeks of verified abstinence. Sixteen non-drug-dependent controls were studied after comparable intervals. SPEM tracking accuracy, estimated by the Ln (S/N) statistic, was higher among cocaine-dependent patients than among alcohol-dependent patients and normal controls. A microanalysis of SPEM tracking revealed that the superior accuracy of the cocaine-dependent group was due to a small increase in eye movements at the target frequency (0.4 Hz) and a small compensatory decrease in higher frequency eye movements (i.e., saccades). In contrast to the findings of the SPEM study, the findings of the SEM study revealed that alcohol-dependent patients constituted the only abnormal group. Alcohol-dependent patients exhibited slower saccade onset latencies than the other groups. There were no significant differences among the groups with respect to saccade velocity, amplitude, or duration.

Lithium effect on smooth pursuit eye movements of healthy volunteers

Smooth pursuit eye movement (SPEM) dysfunctions in major affective disorder patients have been reported to be associated with lithium treatment. We report that SPEM of 13 healthy volunteers, either taking lithium (n = 7) or placebo (n = 6), were not significantly impaired by lithium. This could point to a pathophysiologic difference between affective disorder patients and a normal population.

Behavioral markers of schizophrenia useful for genetic studies

The advent of powerful molecular biological techniques have already led to the discovery of chromosomal loci linked to some genetically transmitted diseases. These techniques, however, lose their power if applied to a disease trait that is not Mendelian in its transmission. The low familial prevalence of psychiatric diseases such as schizophrenia make these techniques unsuitable for linkage studies of these conditions, if identification of schizophrenia relies solely on the clinical manifestation of the schizophrenic psychosis. Broadening the disease phenotype in diseases such as schizophrenia, with low recurrence risk, and narrowing it in diseases such as major affective disorder, with very high recurrence risk, may be an effective strategy for linkage studies of these diseases. Several alternative phenotypes are discussed, including smooth pursuit eye movement abnormalities, event related potentials, and deficient attentional deployment as measured by the continuous performance test. The strategy assumes that schizophrenia is a pleiotropic disorder, and that the psychosis is the rare form of the condition. The paper focuses principally on smooth pursuit eye movement abnormalities, and claims a plausible place for them as an independent expression of schizophrenia. With this strategy, the possibility for successful linkage studies increases, since familial distributions of schizophrenia and pursuit abnormalities, considered together, appear to fit an autosomal dominant pattern.

Effects of lithium treatment on eye movements

Smooth pursuit eye movements (SPEMs) of 11 bipolar manic patients were impaired during lithium treatment, which, however, improved their clinical condition. SPEM impairment was evident in a general qualitative degradation of eye tracking integrity, in a tendency for gain to be lowered, and in an increase in the number of saccadic events. Individual differences in the nature and magnitude of effects of lithium on eye movements were noteworthy.

The relationship between smooth pursuit eye movement impairment and psychological measures of psychopathology

Two hundred and eighty-four male college volunteers were screened for smooth pursuit eyetracking deficiencies, a commonly reported concomitant of schizophrenia. A sample of 36 subjects, weighted with poor eyetrackers, was brought into the National Institute of Mental Health laboratory and retested on electro-oculogram and infrared tracking procedures. They were also administered psychological tests which assessed nine dimensions relevant to schizophrenic, neuropsychological, and affective disorders. In the area of schizophrenia-like symptoms, measures of attention deficits, stimulation avoidance, and identity problems predicted poor eyetracking for the whole sample. Using the poor eyetracking subjects alone (N = 24), interpersonal withdrawal was also significantly related to poor performance but not stimulation avoidance. In the neuropsychological area, measures of attention control and perceptual-motor dysfunction for the total sample, and perceptual problems and general intellectual decrements for the poor eyetrackers were significantly related to poor performance. There was no relationship between measures of affective dysfunction and poor eyetracking.

Combined measure of smooth pursuit eye movements and ventricle-brain ratio in schizophrenic disorders

Smooth pursuit eye movements (SPEM) were examined in 67 schizophrenic patients and 101 control subjects. Our study confirms that eye tracking in schizophrenic patients is impaired compared to that in controls. The similar pattern of distribution of SPEM abnormalities in Italian patients as in ethnically different populations strengthens the hypothesis that these abnormalities may be a biological marker for schizophrenia. We also examined the relationship between SPEM abnormalities and the ventricle-brain ratio (VBR), which is also considered useful for differentiating schizophrenic subgroups. Our preliminary results indicate that there is an inverse correlation between abnormal SPEM performance and ventricular enlargement, suggesting that these abnormalities mark distinct subgroups of patients.

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.

Smooth pursuit eye movement disorder and its psychobiologic correlates in unmedicated schizophrenics

The accuracy of smooth pursuit eye movements (SPEMs) was evaluated electrooculographically in 14 medication-free schizophrenics. Concentrations of monoamine metabolites and gamma-amino-butyric acid (GABA) were measured in their cerebrospinal fluid (CSF). Ventricular-brain ratios (VBR) were determined by computed axial tomography (CT scan). Premorbid adjustment was evaluated by the Phillips Scale. The SPEMs of eight of the patients were reevaluated after 2 weeks of treatment with either prazosin or pimozide. No consistent significant correlations were found between SPEM accuracy and CSF metabolite concentrations, VBR, or premorbid adjustment. SPEM accuracy was not correlated with number of days off medication and was significantly correlated when measured before and during medication.

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.

Frontal lobe dysfunctions in schizophrenia--I. Eye movement impairments

The phenomena of eye movement impairments in schizophrenia are interpreted in this paper, Part I of a two-paper series, in the context of neural mechanisms of attention and eye movement control. The predominant pattern of attention and eye movement impairment in schizophrenia--a disruption of smooth pursuit by saccadic intrusions--is consistent with a disinhibition of saccades. This disinhibition may be related to a dysfunction of frontal eye field mechanisms involved in feedback regulation of saccades and smooth pursuit during visual tracking. A second, less specific type of smooth pursuit impairment consists of saccadic substitution, and may be interpreted in terms of a dysfunction of temporo-parietal mechanisms of task-engagement.

Limit cycle oscillations of the human eye

The altered feedback technique is very suited to display nonlinearities of the human smooth pursuit system. In fact, when the gain of the retinal feedback path is raised, for the horizontal channel, above its normal unitary negative value, a threshold is met beyond which sustained horizontal self-excited smooth oscillations of the eye can be observed, which point out the existence of a stable limit cycle. Furthermore, the characterizing features of both the transient and steady state show a well defined dependence on the total feedback factor K. In particular, the analytical dependence on K of the amplitude and frequency of limit cycle oscillations can be derived. Implications of the experiment with respect to the mathematical modelling of the system are discussed.

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.