Smooth pursuit performance in families with multiple occurrence of schizophrenia and nonpsychotic families

Normative tDCS over V5 and FEF reveals practice-induced modulation of extraretinal smooth pursuit mechanisms, but no specific stimulation effect

The neural networks subserving smooth pursuit eye movements (SPEM) provide an ideal model for investigating the interaction of sensory processing and motor control during ongoing movements. To better understand core plasticity aspects of sensorimotor processing for SPEM, normative sham, anodal or cathodal transcranial direct current stimulation (tDCS) was applied over visual area V5 and frontal eye fields (FEF) in sixty healthy participants. The identical within-subject paradigm was used to assess SPEM modulations by practice. While no specific tDCS effects were revealed, within- and between-session practice effects indicate plasticity of top-down extraretinal mechanisms that mainly affect SPEM in the absence of visual input and during SPEM initiation. To explore the potential of tDCS effects, individual electric field simulations were computed based on calibrated finite element head models and individual functional localization of V5 and FEF location (using functional MRI) and orientation (using combined EEG/MEG) was conducted. Simulations revealed only limited electric field target intensities induced by the applied normative tDCS montages but indicate the potential efficacy of personalized tDCS for the modulation of SPEM. In sum, results indicate the potential susceptibility of extraretinal SPEM control to targeted external neuromodulation (e.g., personalized tDCS) and intrinsic learning protocols.

A possible key role of vision in the development of schizophrenia

Based on a brief overview of the various aspects of schizophrenia reported by numerous studies, here we hypothesize that schizophrenia may originate (and in part be performed) from visual areas. In other words, it seems that a normal visual system or at least an evanescent visual perception may be an essential prerequisite for the development of schizophrenia as well as of various types of hallucinations. Our study focuses on auditory and visual hallucinations, as they are the most prominent features of schizophrenic hallucinations (and also the most studied types of hallucinations). Here, we evaluate the possible key role of the visual system in the development of schizophrenia.

Effects of ketamine on brain function during smooth pursuit eye movements

The uncompetitive NMDA receptor antagonist ketamine has been proposed to model symptoms of psychosis. Smooth pursuit eye movements (SPEM) are an established biomarker of schizophrenia. SPEM performance has been shown to be impaired in the schizophrenia spectrum and during ketamine administration in healthy volunteers. However, the neural mechanisms mediating SPEM impairments during ketamine administration are unknown. In a counter-balanced, placebo-controlled, double-blind, within-subjects design, 27 healthy participants received intravenous racemic ketamine (100 ng/mL target plasma concentration) on one of two assessment days and placebo (intravenous saline) on the other. Participants performed a block-design SPEM task during functional magnetic resonance imaging (fMRI) at 3 Tesla field strength. Self-ratings of psychosis-like experiences were obtained using the Psychotomimetic States Inventory (PSI). Ketamine administration induced psychosis-like symptoms, during ketamine infusion, participants showed increased ratings on the PSI dimensions cognitive disorganization, delusional thinking, perceptual distortion and mania. Ketamine led to robust deficits in SPEM performance, which were accompanied by reduced blood oxygen level dependent (BOLD) signal in the SPEM network including primary visual cortex, area V5 and the right frontal eye field (FEF), compared to placebo. A measure of connectivity with V5 and FEF as seed regions, however, was not significantly affected by ketamine. These results are similar to the deviations found in schizophrenia patients. Our findings support the role of glutamate dysfunction in impaired smooth pursuit performance and the use of ketamine as a pharmacological model of psychosis, especially when combined with oculomotor biomarkers. Hum Brain Mapp 37:4047-4060, 2016. © 2016 Wiley Periodicals, Inc.

Association of variants in DRD2 and GRM3 with motor and cognitive function in first-episode psychosis

Similar smooth pursuit eye tracking dysfunctions are present across psychotic disorders. They include pursuit initiation and maintenance deficits that implicate different functional brain systems. This candidate gene study examined psychosis-related genotypes regulating dopamine and glutamate neurotransmission in relation to these pursuit deficits. One hundred and thirty-eight untreated first-episode patients with a psychotic disorder were genotyped for four markers in DRD2 and four markers in GRM3. The magnitude of eye movement abnormality in patients was defined in relation to performance of matched healthy controls (N = 130). Eighty three patients were followed after 6 weeks of antipsychotic treatment. At baseline, patients with a -141C deletion in DRD2 rs1799732 had slower initiation eye velocity and longer pursuit latency than CC insertion carriers. Further, GRM3 rs274622_CC carriers had poorer pursuit maintenance than T-carriers. Antipsychotic treatment resulted in prolonged pursuit latency in DRD2 rs1799732_CC insertion carriers and a decline in pursuit maintenance in GRM3 rs6465084_GG carriers. The present study demonstrates for the first time that neurophysiological measures of motor and neurocognitive deficits in patients with psychotic disorders have different associations with genes regulating dopamine and glutamate systems, respectively. Alterations in striatal D2 receptor activity through the -141C Ins/Del polymorphism could contribute to pursuit initiation deficits in psychotic disorders. Alterations in GRM3 coding for the mGluR3 protein may impair pursuit maintenance by compromising higher perceptual and cognitive processes that depend on optimal glutamate signaling in corticocortical circuits. DRD2 and GRM3 genotypes also selectively modulated the severity of adverse motor and neurocognitive changes resulting from antipsychotic treatment.

Psychosis in children: diagnosis and treatment

The diagnosis of childhood psychosis raises a host of unresolved problems, despite the Diagnostic and Statistical Manual Of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR) giving identical symptoms and definitions for children, adolescents, and adults. The fantasy lives of children, and issues of developing language and cognition (including retardation), all impair diagnostic accuracy, particularly when differentiating between childhood-onset schizophrenia (COS) (≤12 years), bipolar affective disorder, major depressive disorder, and even obsessive-compulsive disorder and attention-deficit/hyperactivity disorder: the catch-all classification, psychosis not otherwise specified (PNOS), is always available for conundra that prove unsolvable. Typical if nonpathognomonic features include neurocognitive difficulties. Multiple screening instruments and specialized versions of semistructured diagnostic interviews are available. Although smooth-pursuit eye-tracking movements may prove a genetic marker for COS, etiologies are likely to be oligogenetic rather than related to a single gene. No specific biological markers or neuroimages have been identified. As such, psychoses may be indicative of a more general pattern of brain dysfunction. Drug treatments are largely based on the adult literature because of a dearth of controlled data below age 18. There are still no rigorous studies of psychosocial treatments and psychotherapy specific to childhood psychosis.

Contribution of nonprimate animal models in understanding the etiology of schizophrenia

Schizophrenia is a severe psychiatric disorder that is characterized by positive and negative symptoms and cognitive impairments. The etiology of the disorder is complex, and it is thought to follow a multifactorial threshold model of inheritance with genetic and neurodevelop mental contributions to risk. Human studies are particularly useful in capturing the richness of the phenotype, but they are often limited to the use of correlational approaches. By assessing behavioural abnormalities in both humans and rodents, nonprimate animal models of schizophrenia provide unique insight into the etiology and mechanisms of the disorder. This review discusses the phenomenology and etiology of schizophrenia and the contribution of current nonprimate animal models with an emphasis on how research with models of neuro transmitter dysregulation, environmental risk factors, neurodevelopmental disruption and genetic risk factors can complement the literature on schizophrenia in humans.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

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.

Effects of procyclidine on eye movements in schizophrenia

Smooth pursuit eye movement (SPEM) and antisaccade deficits are observed in the schizophrenia spectrum and have been used to study the pathophysiology as well as the genetic basis of this condition. The neurotransmitter acetylcholine has been implicated in a number of cognitive processes thought to underlie SPEM and antisaccade performance. This study investigates effects on eye movements of procyclidine, an anticholinergic drug often administered to schizophrenic patients. A total of 13 patients completed a double-blind placebo-controlled crossover design, receiving 15 mg procyclidine and placebo. Seven participants received procyclidine first and placebo second, six participants were tested in the reverse order. SPEM and antisaccade (as well as fixation and prosaccade) eye movements were recorded using infrared oculography. Results showed that procyclidine overall, relative to placebo, mildly worsened SPEM performance, as indicated by nonsignificantly reduced gain (p=0.08) and increased frequency of intrusive anticipatory saccades during pursuit (p=0.06). A significant interaction of group and order of administration indicated that procyclidine increased the rate of antisaccade reflexive errors only when administered first; the opposite pattern was observed when placebo was administered first, likely due to the operation of practice effects at second assessment. These findings indicate that acute administration of a clinically relevant dose of procyclidine leads to mild impairments in eye movement performance in schizophrenic patients, suggesting the need to consider this compound in oculomotor studies in schizophrenia. The action of this anticholinergic drug on oculomotor performance is consistent with the hypothesized role of the cholinergic system in the cognitive mechanisms of attention and working memory, processes thought to underlie SPEM and antisaccade performance. Effects of order of administration and practice on the antisaccade task suggest that these factors need to be taken into consideration in future pharmacological studies.

Effects of nicotine on leading saccades during smooth pursuit eye movements in smokers and nonsmokers with schizophrenia

Several studies have shown that schizophrenic patients and their biological relatives generate a greater number of leading saccades during smooth pursuit eye movement (SPEM) tasks. This abnormality may reflect a failure of cortical and/or cerebellar areas to coordinate saccadic and pursuit eye movements during visual tracking. The pharmacology of this phenomenon is not known. Here, we sought to replicate and extend the findings of Olincy et al (1998), who found that nicotine transiently reduced the number of leading saccades during SPEMs. A total of 27 subjects with schizophrenia (17 males; 14 smokers), and 25 healthy comparison subjects (nine males; 14 smokers) completed an eye-tracking task after receiving a 1.0 mg nasal spray of nicotine and during drug-free conditions. Results confirm that nicotine reduces the number of leading saccadic eye movements during visual tracking in schizophrenic patients. Baseline impairments and the beneficial effects of nicotine were not restricted to patient smokers, as nonsmoker patients exhibited the greatest number of leading saccades in the no drug condition and exhibited the most pronounced improvements after nicotine administration. Improvement in patient nonsmokers was not a function of previous smoking history. No effect of nicotine was observed in control nonsmokers. In contrast to the previous study, nicotine appeared to improve performance in control smokers. Overall, the study results support a functional role of nACh receptors in improving eye-tracking performance, and are consistent with the hypothesis, articulated by several investigators, that nACh receptor system abnormalities are responsible for a number of schizophrenia-related neurophysiological deficits.

Reliability of smooth pursuit, fixation, and saccadic eye movements

The present study investigated the reliability and susceptibility to practice effects of oculomotor tasks. Smooth pursuit, fixation, antisaccade, and prosaccade tasks were administered to 31 healthy participants to assess internal consistency (Cronbach's alpha) and within-session practice effects. Twenty-one of these participants were retested after an average interval of 57.86 days to assess temporal stability and between-session practice effects. Internal consistencies were high for most measures, with few within-session performance changes. Test-retest reliabilities of most measures were good. Between-session practice effects were most consistently observed on the antisaccade task, indicated by reduced error rate and improved spatial accuracy at retest. Magnitude of improvement on these measures was related to performance, indicating that poor performers benefited most from repeated assessment. These findings support the trait nature of oculomotor function and point to the need to take into consideration between-session practice effects on the antisaccade task in longitudinal studies.

Schizophrenia spectrum disorders and eye tracking dysfunction in singleton and multiplex schizophrenia families

One line of research which is helping to unravel the genetic susceptibility to schizophrenia (SZ) is the analysis of eye tracking dysfunction (ETD), a quantifiable phenotypic marker. To investigate if such a biological marker is also present in singleton schizophrenia families, we examined eye tracking in members of singleton families (N=53) and compared it to members of multiplex (N=76) and nonpsychiatric families (N=71) using high resolution infrared oculography. The prevalence of ETD defined by gain values (eye/target velocity) and saccadic frequencies during smooth pursuit at 15 degrees /s did not differ between multiplex and singleton families in either the schizophrenic index patients or their relatives, but was significantly different from nonpsychotic families. ETD rate was higher in those relatives with compared to those without a diagnosis of a schizophrenia spectrum disorder. In relatives with a spectrum disorder, ETD appeared to be associated with traits for "sensitivity" and "suspiciousness". In the group of relatives from singleton families without a schizophrenia spectrum disorder, we still found a higher prevalence of ETD than in nonpsychotic families. Our results suggest that eye tracking dysfunction is a very sensitive biological marker for the vulnerability to schizophrenia, even in those cases where no psychopathological symptoms or signs are obvious. ETD in schizophrenia is suggested to serve as a neurophysiological type model, indicating a perception deficit.

Eye-tracking dysfunction (ETD) in families with sporadic and familial schizophrenia

BACKGROUND

Within the field of genetic schizophrenia research, eye-tracking dysfunction can be regarded as a putative trait marker in families with multiple occurrences of the disease (familial schizophrenia). We concentrated on families with single occurrences of schizophrenia (sporadic schizophrenia) to test whether a genetic factor may be present in these families as well.

METHODS

Eye movements were recorded using infrared oculography in eight families with sporadic schizophrenia (44 members), eight families with familial schizophrenia (66 members), and nine nonpsychotic families (77 members). Triangle-wave stimuli at 15 degrees /sec and 30 degrees /sec were used, and gains (eye velocity/target velocity), rates, and amplitudes of saccades (classified as catch-up and anticipatory saccades) were determined.

RESULTS

1) In sporadic-schizophrenia families, gain values, saccade rates, and anticipatory saccade amplitudes at 30 degrees /sec differed in a statistically significant fashion from nonpsychotic families, but not from families with multiple occurrences of schizophrenia, and 2) at 30 degrees /sec, a significant effect of target direction on smooth-pursuit maintenance was observed in both sporadic- and familial-schizophrenia families.

CONCLUSIONS

Our results support the hypothesis that genetic factors may be present even in sporadic-schizophrenia families and may contribute to a more precise and biologically based definition of the schizophrenia phenotype in future molecular genetic analysis.