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

The Role of Dopamine in Anticipatory Pursuit Eye Movements: Insights from Genetic Polymorphisms in Healthy Adults

There is a long history of eye movement research in patients with psychiatric diseases for which dysfunctions of neurotransmission are considered to be the major pathologic mechanism. However, neuromodulation of oculomotor control is still hardly understood. We aimed to investigate in particular the impact of dopamine on smooth pursuit eye movements. Systematic variability in dopaminergic transmission due to genetic polymorphisms in healthy subjects offers a noninvasive opportunity to determine functional associations. We measured smooth pursuit in 110 healthy subjects genotyped for two well-documented polymorphisms, the COMT Val¹⁵⁸Met polymorphism and the SLC6A3 3′-UTR-VNTR polymorphism. Pursuit paradigms were chosen to particularly assess the ability of the pursuit system to initiate tracking when target motion onset is blanked, reflecting the impact of extraretinal signals. In contrast, when following a fully visible target sensory, retinal signals are available. Our results highlight the crucial functional role of dopamine for anticipatory, but not for sensory-driven, pursuit processes. We found the COMT Val¹⁵⁸Met polymorphism specifically associated with anticipatory pursuit parameters, emphasizing the dominant impact of prefrontal dopamine activity on complex oculomotor control. In contrast, modulation of striatal dopamine activity by the SLC6A3 3′-UTR-VNTR polymorphism had no significant functional effect. Though often neglected so far, individual differences in healthy subjects provide a promising approach to uncovering functional mechanisms and can be used as a bridge to understanding deficits in patients.

Vergence eye movements in patients with schizophrenia

Previous studies have shown that smooth pursuit eye movements are impaired in patients with schizophrenia. However, under normal viewing conditions, targets move not only in the frontoparallel plane but also in depth, and tracking them requires both smooth pursuit and vergence eye movements. Although previous studies in humans and non-human primates suggest that these two eye movement subsystems are relatively independent of one another, to our knowledge, there have been no prior studies of vergence tracking behavior in patients with schizophrenia. Therefore, we have investigated these eye movements in patients with schizophrenia and in healthy controls. We found that patients with schizophrenia exhibited substantially lower gains compared to healthy controls during vergence tracking at all tested speeds (e.g. 0.25 Hz vergence tracking mean gain of 0.59 vs. 0.86). Further, consistent with previous reports, patients with schizophrenia exhibited significantly lower gains than healthy controls during smooth pursuit at higher target speeds (e.g. 0.5 Hz smooth pursuit mean gain of 0.64 vs. 0.73). In addition, there was a modest (r≈0.5), but significant, correlation between smooth pursuit and vergence tracking performance in patients with schizophrenia. Our observations clearly demonstrate substantial vergence tracking deficits in patients with schizophrenia. In these patients, deficits for smooth pursuit and vergence tracking are partially correlated suggesting overlap in the central control of smooth pursuit and vergence eye movements.

Towards improved animal models for evaluating social cognition and its disruption in schizophrenia: the CNTRICS initiative

Social cognition refers to processes used to monitor and interpret social signals from others, to decipher their state of mind, emotional status and intentions, and select appropriate social behaviour. Social cognition is sophisticated in humans, being embedded with verbal language and enacted in a complex cultural environment. Its disruption characterises the entire course of schizophrenia and is correlated with poor functional outcome. Further, deficits in social cognition are related to impairment in other cognitive domains, positive symptoms (paranoia and delusions) and negative symptoms (social withdrawal and reduced motivation). In light of the significance and inadequate management of social cognition deficits, there is a need for translatable experimental procedures for their study, and identification of effective pharmacotherapy. No single paradigm captures the multi-dimensional nature of social cognition, and procedures for assessing ability to infer mental states are not well-developed for experimental therapeutic settings. Accordingly, a recent CNTRICS meeting prioritised procedures for measuring a specific construct: "acquisition and recognition of affective (emotional) states", coupled to individual recognition. Two complementary paradigms for refinement were identified: social recognition/preference in rodents, and visual tracking of social scenes in non-human primates (NHPs). Social recognition is disrupted in genetic, developmental or pharmacological disease models for schizophrenia, and performance in both procedures is improved by the neuropeptide oxytocin. The present article surveys a broad range of procedures for studying social cognition in rodents and NHPs, discusses advantages and drawbacks, and focuses on development of social recognition/preference and gaze-following paradigms for improved study of social cognition deficits in schizophrenia and their potential treatment.

Pharmacological treatment effects on eye movement control

The increasing use of eye movement paradigms to assess the functional integrity of brain systems involved in sensorimotor and cognitive processing in clinical disorders requires greater attention to effects of pharmacological treatments on these systems. This is needed to better differentiate disease and medication effects in clinical samples, to learn about neurochemical systems relevant for identified disturbances, and to facilitate identification of oculomotor biomarkers of pharmacological effects. In this review, studies of pharmacologic treatment effects on eye movements in healthy individuals are summarized and the sensitivity of eye movements to a variety of pharmacological manipulations is established. Primary findings from these studies of healthy individuals involving mainly acute effects indicate that: (i) the most consistent finding across several classes of drugs, including benzodiazepines, first- and second- generation antipsychotics, anticholinergic agents, and anticonvulsant/mood stabilizing medications is a decrease in saccade and smooth pursuit velocity (or increase in saccades during pursuit); (ii) these oculomotor effects largely reflect the general sedating effects of these medications on central nervous system functioning and are often dose-dependent; (iii) in many cases changes in oculomotor functioning are more sensitive indicators of pharmacological effects than other measures; and (iv) other agents, including the antidepressant class of serotonergic reuptake inhibitors, direct serotonergic agonists, and stimulants including amphetamine and nicotine, do not appear to adversely impact oculomotor functions in healthy individuals and may well enhance aspects of saccade and pursuit performance. Pharmacological treatment effects on eye movements across several clinical disorders including schizophrenia, affective disorders, attention deficit hyperactivity disorder, Parkinson's disease, and Huntington's disease are also reviewed. While greater recognition and investigation into pharmacological treatment effects in these disorders is needed, both beneficial and adverse drug effects are identified. This raises the important caveat for oculomotor studies of neuropsychiatric disorders that performance differences from healthy individuals cannot be attributed to illness effects alone. In final sections of this review, studies are presented that illustrate the utility of eye movements for use as potential biomarkers in pharmacodynamic and pharmacogenetic studies. While more systematic studies are needed, we conclude that eye movement measurements hold significant promise as tools to investigate treatment effects on cognitive and sensorimotor processes in clinical populations and that their use may be helpful in speeding the drug development pathway for drugs targeting specific neural systems and in individualizing pharmacological treatments.

Are eye movement abnormalities indicators of genetic vulnerability to schizophrenia?

Fifty to eighty-five percent of schizophrenic patients are impaired on ocular pursuit paradigms. However, results regarding the relatives are more discordant. The aim of this study was to investigate whether eye movement disorders could be a vulnerability marker of schizophrenia.

METHOD

Twenty-one schizophrenic patients (DSM-IV), 31 first-degree relatives of those patients without schizophrenic spectrum disorders, and two groups of healthy controls matched by age and sex were included. Three oculomotor tasks (smooth pursuit, reflexive saccades and antisaccades) were used.

RESULTS

Patients had a lower averaged gain (P= 0.035) during smooth pursuit than controls, made less correct visually guided saccades (P< 0.001) and more antisaccades errors (P= 0.002) than controls. In contrast, none of the comparison between the relatives and their controls was significant.

CONCLUSION

Schizophrenic patients were impaired on smooth pursuit and antisaccade paradigms. None of these impairments was, however, observed in their first-degree relatives. Our results suggest that the eye movement parameters tested could not be considered as vulnerability markers for schizophrenia.

Linkage of eye movement dysfunction to chromosome 6p in schizophrenia: additional evidence

Establishing the genetics of physiological traits associated with schizophrenia may be an important first step in building a neurobiological bridge between the disease phenotype and its genetic underpinnings. One of the best known of the traits associated with schizophrenia is a disorder of smooth pursuit eye tracking (ETD), which is present in 50-80% of schizophrenia patients. ETD is more than three times more prevalent in the families of a schizophrenia patient than is schizophrenia itself. Arolt et al. [1999] estimated LOD scores for ETD of 2.85 for D6S282 and 3.70 for D6S271, two markers on 6p21.1, as well as obtaining an indication of possible linkage for schizophrenia. Our sample comprised two large families in Denmark. Markers in the region that was implicated by the study of Arolt et al. [1996, 1999] were analyzed as part of a genome scan using the "latent trait (L.T.) model" for the co-transmission of schizophrenia and ETD that we had previously fitted to segregation analysis data from Norway. We obtained a LOD score of 2.05 for D6S1017, a marker within 3 cM of the positive markers obtained by Arolt et al. [1996, 1999]. We regard our results as independent evidence supporting the findings of Arolt et al. [1996, 1999] and also as support for the L.T. model as a way of combining the traits ETD and schizophrenia.

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).

Antisaccades and smooth pursuit eye movements in schizophrenia

Saccadic and smooth pursuit eye movements were recorded in schizophrenic patients, nonschizophrenic psychiatric patients, and normal controls. Both schizophrenic subjects and psychiatric controls demonstrated greater increases in error rates and greater delays in generating antisaccades than did normal controls. Schizophrenic patients with impaired smooth pursuit tracking showed greater increases in error rates in the antisaccade task than did schizophrenic patients with normal pursuit. Among psychiatric controls, increased errors on the antisaccade task were unrelated to pursuit performance. The small size of this group, however, reduces the power to detect a relation between smooth pursuit tracking and performance on the antisaccade task. Although most patients were receiving one or more medications, some of which can affect eye movements, medication state in this study did not account for differences we report in dependent variables.

The effects of remoxipride and chlorpromazine on eye movements and psychomotor performance in healthy volunteers

Fifteen healthy male volunteers received single doses of 100 mg immediate release remoxipride (IR), 150 mg controlled release remoxipride (CR), 50 mg chlorpromazine (CPZ), 2 mg lorazepam (LZ), and placebo in a randomised, five-period cross-over study. Both saccadic (SEM) and smooth pursuit eye movements (SPEM) as well as a battery of psychomotor performance tests were assessed at 1.5-h intervals over 9 h following drug administration. The areas under the response-time curves and the maximum effect during the study period were analysed by analysis of variance. The most consistent impairments were produced by LZ. The neuroleptics caused impairments to SEM, and tended to impair critical flicker fusion, continuous attention and both paced and unpaced versions of the digit-symbol substitution test as well as subjective measures of sedation. Only LZ impaired SPEM. Neither paced nor unpaced psychomotor tests distinguished between neuroleptics and benzodiazepines. The low therapeutic doses of IR and CR produced similar impairments to a sub-therapeutic dose of CPZ. Selectivity of pharmacological action does not appear to predict selectivity of effect on psychomotor function.

Comparison of the smooth eye tracking disorder of schizophrenics with that of nonhuman primates with specific brain lesions

The smooth pursuit eye tracking deficit (ETD) often associated with schizophrenia has generated enormous interest over the last 20 years. The deficit is observed in about 80% of schizophrenics and in half of their first degree relatives. It is not affected by neuroleptic medication and is not due to inattention. A review of 52 studies (and actual records when available) on ETD in schizophrenia reveals that the deficit can consistently be described as low gain pursuit augmented with catch-up saccades and often peppered with intrusive saccades. A review of the brain areas that have been shown to be involved in pursuit provides the necessary background for the subsequent section which details the nature of the smooth tracking deficits following experimental lesions. This section reveals that the ETD following lesions of the frontal lobe is unique in that it closely resembles the ETD of schizophrenics. This finding lends further support for frontal lobe theories of schizophrenia.

The duration of the movement aftereffect as an index of psychiatric illness

The duration of the movement aftereffect (MAE) has sometimes been used to make inferences about the subject's state (for example, their level of arousal). Some studies are reviewed in which visual aftereffects (including the MAE) were measured in schizophrenia, with inconsistent results. Some relevant psychopharmacological and neurological evidence is considered. It is concluded that: (i) Differences in the clinical status of the schizophrenic subjects and whether they were receiving medication, but not the method used to measure aftereffects, may underlie the interstudy disagreements. (ii) The effect of schizophrenia is to increase MAE duration, and this is not due to some peripheral artefact. (iii) Longer MAEs in the illness could result from enhanced neurally signalled contrast and/or from the increased adaptability of cortical neurons.

Effects of pharmacologic catecholamine manipulation on smooth pursuit eye movements in normals

The pathophysiology of schizophrenia may be related directly or indirectly to abnormal dopaminergic activity. Both subcortical excess and frontal cortical deficiency of dopamine have been suggested, and primary or downstream failures of dopamine activation to the prefrontal cortex has been posited to explain some of the cognitive deficiencies in schizophrenia patients. Although the prefrontal cortex may also be a site for the disruption of smooth pursuit eye movements (SPEM), the most substantially described psychophysiological marker for schizophrenia vulnerability, no relationship of SPEM to dopaminergic activity has been demonstrated. In this study we explored the effect of altered dopamine function on SPEM quality through pharmacological manipulation of catecholamine tone in 11 healthy subjects. The subjects had SPEM measured at baseline, and under challenge conditions including amphetamine (0.3 mg/kg), haloperidol (2 mg), placebo, and combined amphetamine with haloperidol. Changes in the profile of mood scale (POMS) confirmed the expected subjective central nervous system effects the agents. Placebo and amphetamine had no effect on qualitative ratings of SPEM, but haloperidol, alone and in combination with amphetamine, disrupted eye tracking, producing a pattern of small saccadic intrusions characteristic of patients with schizophrenia. These findings link dopaminergic blockade with SPEM disruption in normal subjects.

SPEM impairment in drug-naive schizophrenic patients: evidence for a trait marker

Smooth-pursuit eye movements (SPEM) were assessed in healthy subjects and in drug-naive, chronic, and residual schizophrenic patients. SPEM gain was found to be decreased in all the schizophrenic patients who also exhibited a significant increase in the rate of saccades. The frequency of square-wave jerks was the same in schizophrenic patients and normal controls, suggesting that the primary abnormality in schizophrenic patients was a low gain rather than a defect of the saccadic system. Patients were retested 1 month later, and stability of gain was high even in formerly drug-naive subjects who had been treated for 1 month with neuroleptic drugs. Altogether these results confirm the conclusions of most previous studies, extend them to drug-naive schizophrenic patients, and favor the hypothesis that SPEM impairment is a trait marker in schizophrenia.

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.

Abnormalities of smooth pursuit and saccadic control in schizophrenia and affective disorders

Smooth pursuit abnormalities have been reported in patients with schizophrenia and their first-degree relatives, suggesting that abnormal tracking may serve as a biological marker for schizophrenia. Recent studies in schizophrenic patients have found reduced pursuit gain, low initial acceleration and abnormal gain-corrective saccade interactions. Impaired saccadic initiation has been noted in anti-saccade tasks and in predictive saccade generation, as has saccadic hypometria. While abnormalities have been found in affective disorder patients, studies of their first-degree relatives suggest that abnormalities during pursuit are more closely associated with schizophrenia. Identification of specific defects allows informed speculation about their neural substrates and suggests possible relationships between the ocular motor defects and other cognitive and perceptual abnormalities associated with the major psychiatric disorders.

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.

Attentional markers of vulnerability to schizophrenia: performance of medicated and unmedicated patients and normals

Medicated and unmedicated schizophrenic patients (both n's = 14) were compared to a normal control sample (n = 15) on two attentional tasks hypothesized to be markers of vulnerability to schizophrenia. These tasks, the continuous performance test and the visual backward masking task, were found to be more deviant in schizophrenic patients than in normals. In addition, the group mean levels of performance did not differ consistently across medication status within the medicated patients. It was found, however, that the association between these tasks varied as a function of medication status, with unmedicated patients more similar to normals than to medicated patients. The implications of these results for the two tasks as markers are discussed, with special focus on those earlier studies that did not evaluate unmedicated patients.

Monologue speech: effects of d-amphetamine, secobarbital and diazepam

Drugs of abuse from different pharmacological classes increase social conversation. Alcohol and d-amphetamine also increase rates of talking in subjects producing speech monologues in an isolated context. This latter finding suggests that the increases observed during dyadic social conversation may represent general increases in talking and not specific effects on social interaction. The present study was conducted to assess whether other abused drugs also increase monologue speaking. The acute effects of secobarbital (0, 50, 150, 250 mg), d-amphetamine (0, 25 mg) (Experiment 1), and diazepam (0, 10, 20, 40 mg) (Experiment 2) were investigated in healthy, adult volunteers. Secobarbital and d-amphetamine both increased the total amount of speech emitted, while diazepam generally had no effect or decreased talking. Experiment 3 was conducted to further compare the effects of secobarbital (0, 50, 150, 250 mg) and diazepam (0, 5, 15, 25 mg) using a within-subject, crossover design. Secobarbital increased talking in three of the four subjects studied, while diazepam, again, had no effect or decreased talking. In contrast to the differences noted with talking, secobarbital and diazepam both decreased response rates in a nonverbal performance task (i.e., circular-lights procedure); they also produced many similar effects on various subject-rated measures of drug effect. Thus, the differences in the effects of these two compounds on talking are not the result of a general difference in their overall profile of behavioral effects. In summary, the results obtained with secobarbital and d-amphetamine further demonstrate that an explicitly social context is not a necessary condition to observe drug-produced increases in speech quantity. The failure of diazepam to reliably increase talking in the present study illustrates the existence of some pharmacological specificity in the effect of drugs on human speech, and suggests another way in which the behavioral effects of the barbiturates and benzodiazepines may differ.

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.

Changes in eye tracking during clinical stabilization in schizophrenia

Eye tracking abnormalities have been proposed as a trait marker for schizophrenia on the basis of their familial prevalence and the consistency of tracking over time in clinically stable patients. However, few studies have examined stability through acute episodes of illness, and most studies have not analyzed changes in different forms of eye movements. Therefore, the authors examined eye tracking, clinical state, and neuroleptic dose during 4 consecutive weeks in nine recently hospitalized schizophrenic patients. For the patients and controls, qualitative ratings of pursuit accuracy remained relatively stable over time. In contrast, saccade frequency increased significantly, with a 57% increase in small saccades and a 77% reduction in larger saccades. In comparison with cross-sectional studies which have found no correlation between neuroleptic dose and tracking performance, a reduction in large saccades was strongly correlated with increase in neuroleptic dose. The findings suggest that pursuit accuracy may be a trait characteristic of schizophrenia, while the frequency and size of saccades are state dependent characteristics.

Dark condition normalization of smooth pursuit tracking: evidence of cerebellar dysfunction in psychosis

Smooth pursuit tracking performance was evaluated in psychotic (n = 20) and normal control subjects (n = 20) during light and dark testing conditions using computer-based analyses of electrographically recorded tracking patterns. Previously reported impaired tracking in psychotics tested under light conditions was reaffirmed. However, the tracking patterns of patients during the dark condition not only resembled those of controls under similar conditions, but were no longer significantly different from controls' light condition performance. Among several possible bases for these results which are considered, the involvement of cerebellar dysfunction in these patients is emphasized.

Catecholamines and attention. I: Animal and clinical studies

One important function of the catecholamine innervation of the cerebral cortex may be the control of attention. Of particular interest are the catecholamine projections to the cerebral cortex from the reticular formation, namely the dopamine neurons of the ventral tegmentum of the midbrain and the noradrenergic neurons of the locus coeruleus in the upper pons. Animal studies implicate noradrenaline and dopamine in a wide range of attention-related behaviours involving search and exploratory activity, distractibility, response rate, discriminability and the switching of attention. Most human studies come from the clinical literature relating to schizophrenia, Parkinson's disease and attention deficit disorder. An association has been claimed in each of these conditions between abnormal catecholamine activity (in particular dopamine) and attentional dysfunction. In particular, difficulty with the attachment of appropriate responses to environmental stimuli, akin to those observed in animals with lesions to central dopamine pathways, indicates a role for dopamine in response selection processes. Overall, the animal and human studies reviewed indicate a role for central noradrenaline and dopamine in the early and late processing of information, respectively.

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.

Eye-tracking, attention and amphetamine challenge

Smooth pursuit eye movement (SPEM) performance has been linked to nonvoluntary attentional processes. Amphetamine is a psychotropic drug with documented effects on attentional performance. In order to evaluate the relationship between SPEM performance and amphetamine's attentional effects, SPEM performance was measured prior to and following amphetamine administration in five bipolar patients and eight obsessive-compulsive patients. In these 13 patients, amphetamine did not significantly alter the accuracy of SPEM in the two patient groups. However, significant negative correlations were observed in the obsessive-compulsive patients and in the combined patient groups between baseline SPEM impairment and changes in eye-tracking accuracy following amphetamine, i.e. individuals with poorer SPEM accuracy improved while better SPEM performers deteriorated in tracking accuracy during amphetamine treatment.

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.

Smooth pursuit eye tracking, neuropsychological test performance, and computed tomography in schizophrenia

Smooth pursuit eye movements (SPEM) were measured in 18 patients who met Research Diagnostic Criteria for schizophrenia. Some degree of SPEM impairment was present in most patients. Deviant eye tracking was not related to ratings of severity of illness, but was related to recurrent episodes of hospitalization, antipsychotic medication, and lower ratings in anxiety and delusions. Worse SPEM tended to be associated with larger lateral ventricles as assessed on computed tomography. Three patients with reversed occipital asymmetry had more deviant eye tracking than the remaining patients. Eye movement impairment was related to worse performance in Finger Tapping and in the Trail-Making Test, and to fewer perceived alternations of a Necker cube, suggesting that frontoparietal disturbances are related to poor pursuit eye tracking in schizophrenia.

Vestibular activation, smooth pursuit tracking, and psychosis

Pursuit tracking and vestibular activation procedures were combined in an investigation to determine if smooth pursuit tracking deficits could be related to abnormalities of visual-vestibular interaction in psychiatric patients. In actively psychotic patients, but not in comparison groups of schizophrenic outpatients with remitted symptomatology or normal controls, a significant failure of visual fixation to suppress caloric nystagmus was related to a higher incidence of disordered tracking during both baseline and postirrigation conditions. Other vestibular irregularities including dysrhythmia and reduced fast phase velocity were observed in these same patients. The results are supportive of a central deficit in visual-vestibular interaction that may contribute to pursuit tracking deficits in psychosis.

Eye movements of teenage children of schizophrenics: a possible inherited marker of susceptibility to the disease

Teenage children each having one schizophrenic parent showed deficits in oculomotor control which are also found in schizophrenic subjects compared with controls. They made significantly more saccadic eye movements interrupting smooth pursuit ocular tracking. They also made significantly more double-jump saccadic movements in a looking task. Since this latter difference was true only when the visual target was illuminated during the saccade (p less than 0.001), the cause was likely visual processing and not a fixation stability problem. The two measures correlated significantly for all subjects (r = 0.63), and half the experimentals had scores more than two standard deviations above the mean for controls. This suggests that a pattern of oculomotor dysfunction found in schizophrenics which comes from a single source may act as a marker for susceptibility of their offspring to the disease.

Motor control of schizophrenics--II. Manual control and tracking: sensory and motor deficits

Manual control and tracking of 12 acute and chronic schizophrenics was tested for comparison with their performance in oculomotor tracking. Schizophrenics tended to be slower in a non-timed, non-tracking hand movement, and chronics made even slower movement when the experimental room was illuminated than when it was darkened. Chronics also had a significantly higher reaction time than normal controls. When tracking a constant-velocity visual target, all schizophrenics were significantly slower than normals to high-velocity (50 degrees and 60 degrees/s) targets only. When tracking a sinusoidally moving target, schizophrenics were not less accurate over-all but they showed less improvement than normals when room illumination gave visual information about background and hand position. This complex group of motor deficiencies of schizophrenics, along with their oculomotor control problems, suggests that they have sensory processing, attentional, and motor planning problems when performing orienting tasks.

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.

Benzodiazepines impair smooth pursuit eye movements

Five healthy male volunteers received single oral doses of 10 mg diazepam, 20 mg temazepam and placebo, in a double-blind, randomised fashion. Smooth pursuit eye movement velocity and serum benzodiazepine concentration were measured before and after at 0.5,1,1.5,2,3,4,6,9 and 12 h after administration of the treatments. Significant decrease in smooth pursuit eye movement velocity as compared to placebo was observed between 0.5-2 h after temazepam, and between 1-2 h after diazepam. Smooth pursuit eye movement velocity was log-linearly correlated with serum temazepam and diazepam concentration. The results demonstrate the relationship between serum benzodiazepine concentration and its effect on an objective measure of oculomotor performance.

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.

Disturbed smooth pursuit and saccadic eye movements in schizophrenia

Smooth pursuit and saccadic eye movements of schizophrenic patients were examined. In a pendulum (0.5 Hz) tracking task schizophrenic inpatients had a slightly lower smooth pursuit gain than outpatients and controls, who showed no significant differences. The number of saccades, counter-saccades and velocity arrests occurring in a 20 s tracking epoque was the same in patients and controls, but patients made larger saccades. When tracking a stepping target by saccadic eye movements, schizophrenic inpatients, and to a lesser extent outpatients, exhibited longer reaction times than controls and had a higher incidence of "non-fixation" (saccades away from the target while the target is stationary). Schizophrenic patients also showed a significantly larger proportion of dysmetric saccades (undershooting the target). While similar changes of reaction time and non-fixation score were observed in manic-depressives and alcoholics, dysmetria was more often found in schizophrenics and possibly constitutes the expression of a specific impairment of attention.

Motor control of schizophrenics--I. Oculomotor control of schizophrenics: a deficit in sensory processing, not strictly in motor control

An in-depth analysis of eye movements of schizophrenics has demonstrated defects in several oculomotor subsystems, likely due to processing of sensory information and not to problems in the motor system itself. Schizophrenic subjects made more pursuit tracking errors, due to higher RMS errors, larger phase lag, and more saccades in pursuit. When making saccadic movements they had normal reaction times, saccade velocity and intersaccadic pause, but made more double-jump saccades and overshot the target. Only some had inability to hold steady fixation, but all had an attentional problem in restraining an inappropriate eye movement. The multiple defects suggest a processing problem that is not strictly motor and does not fit any standard definition of attention.

Flickering light spot as a tracking target for the study of smooth pursuit eye movements in schizophrenics--a new method

Smooth pursuit eye movements (SPEM) were studied in 26 schizophrenics and 20 normal controls. A light spot on a screen of cathode ray oscilloscope was used as a tracking target. In order to induce SPEM disorder easily, the subjects were required to track a light spot which flickered in various frequencies. This new method devised by the authors has clearly demonstrated that the SPEM in schizophrenic was more profoundly disturbed by the flickering of the tracking target than that in the normal control subjects. It was supposed that poor tracking of a flickering light spot in schizophrenics may be due to the inadequate concentration of attention to visual stimuli, and/or inability to predict the movements of a tracking target.

Smooth pursuit eye movements among storage battery workers

Eleven male workers in a battery storage plant with lead and erythrocyte protoporphyrin blood actual levels greater than 50 and 100 micrograms %, respectively, and 18 male controls without lead exposure were tested by a clinical pendular eye tracking test (PETT). Each worker underwent a series of lead absorption measurements including blood lead, urinary lead, erythrocyte protoporphyrin, delta-aminolevulinic acid dehydratase activity, and urinary delta-aminolevulinic acid. The SPEMs were evaluated by an eye tracking technique. The subjects followed a horizontally moving target which, in the form of a luminous spot on a dark background, was projected onto a screen placed 1 m from the subject. The maximum predicted eye movement velocity during tracking was about 30 degrees/s. Skin electrodes were applied on the outer canthi of both eyes and SPEM were plotted on a polygraph, recording both the actual eye movements and the corresponding first derivative. Our findings suggest that lead workers display a disorder of motor coordination of SPEMs system, and the PETT is useful, when associated with biochemical data, to evaluate the degree of subclinical damage of nervous system during lead poisoning.

Horizontal and vertical pursuit eye movements, the oculocephalic reflex, and the functional psychoses

Sixteen schizophrenic patients, 16 manic-depressive patients, and 14 nonpatient control subjects were tested for horizontal and vertical smooth pursuit eye movements (SPEM) and the oculocephalic reflex. All patients with impaired horizontal pursuit also displayed disrupted vertical pursuit, suggesting that a common mechanism underlies these abnormalities. The oculocephalic reflex was intact in 96% of the subjects whether or not pursuit was disrupted, suggesting that the locus of the eye movement disorder in psychosis may be cortical. For horizontal pursuit, there were significant differences between schizophrenics and nonpatient controls, and between manic depressives and nonpatient controls, but not between schizophrenics and manic depressives, suggesting that the SPEM disruption occurs with significant prevalence in major functional psychoses and not only in schizophrenia.

Target velocity and smooth pursuit eye movements in psychiatric patients

Smooth pursuit tracking performance of psychiatric patients and non-hospitalized normal controls was compared for targets oscillating at 0.45 Hz and 0.31 Hz. Psychiatric inpatients exhibited significantly more velocity arrests than psychiatric outpatients or normals under both conditions. Tracking performance of all groups at 0.31 Hz was improved relative to that at 0.45 Hz, but significant improvement occurred only for outpatients and normals. The role of attentional and stimulus factors in the tracking performance or psychiatric patients is discussed.