Smooth pursuit eye movement, prepulse inhibition, and auditory paired stimuli processing endophenotypes across the schizophrenia-bipolar disorder psychosis dimension

Oculomotor Abnormalities and Aberrant Neuro-Developmental Markers: Composite Endophenotype for Bipolar I Disorder: Anomalies Oculomotrices et Marqueurs Neuro-Développementaux Aberrants : Endophénotype Composite du Trouble Bipolaire I

BACKGROUND

Neurological soft signs (NSSs), minor physical anomalies (MPAs), and oculomotor abnormalities were plausible biomarkers in bipolar disorder (BD). However, specific impairments in these markers in patients after the first episode mania (FEM), in comparison with first-degree relatives (high risk [HR]) of BD and healthy subjects (health control [HC]) are sparse.

AIM OF THE STUDY

This study aimed at examining NSSs, MPAs, and oculomotor abnormalities in remitted adult subjects following FEM and HR subjects in comparison with matched healthy controls. Investigated when taken together, could serve as composite endophenotype for BD.

METHODS

NSSs, MPAs, and oculomotor abnormalities were evaluated in FEM (n = 31), HR (n = 31), and HC (n = 30) subjects, matched for age (years) (p = 0.44) and sex (p = 0.70) using neurological evaluation scale, Waldrop's physical anomaly scale and eye tracking (SPEM) and antisaccades (AS) paradigms, respectively.

RESULTS

Significant differences were found between groups on NSSs, MPAs, and oculomotor parameters. Abnormalities are higher in FEM subjects compared to HR and HC subjects. Using linear discriminant analysis, all 3 markers combined accurately classified 72% of the original 82 subjects (79·2% BD, 56·70% HR, and 82·1% HC subjects).

CONCLUSIONS

AS and SPEM could enhance the utility of NSSs, and MPAs as markers for BD. The presence of these abnormalities in FEM suggests their role in understanding the etiopathogenesis of BD in patients who are in the early course of illness. These have the potential to be composite endophenotypes and have further utility in early identification in BD.

Reduced amplitude and slowed latency of the acoustic startle response in adolescents and adults with 22q11.2 deletion syndrome

BACKGROUND

22q11.2 deletion syndrome (22q11DS) is one of the most robust genetic predictors of psychosis and other psychiatric illnesses. In this study, we examined 22q11DS subjects' acoustic startle responses (ASRs), which putatively index psychosis risk. Latency of the ASR is a presumptive marker of neural processing speed and is prolonged (slower) in schizophrenia. ASR measures correlate with increased psychosis risk, depend on glutamate and dopamine receptor signaling, and could serve as translational biomarkers in interventions for groups at high psychosis risk.

METHODS

Startle magnitude, latency, and prepulse inhibition were assessed with a standard acoustic startle paradigm in 31 individuals with 22q11.2DS and 32 healthy comparison (HC) subjects. Surface electrodes placed on participants' orbicularis oculi recorded the electromyographic signal in ASR eyeblinks. Individuals without measurable startle blinks in the initial habituation block were classified as non-startlers.

RESULTS

Across the startle session, the ASR magnitude was significantly lower in 22q11DS subjects than HCs because a significantly higher proportion of 22q11DS subjects were non-startlers. Latency of the ASR to pulse-alone stimuli was significantly slower in 22q11DS than HC subjects. Due to the overall lower 22q11DS startle response frequency and magnitudes prepulse inhibition could not be analyzed.

CONCLUSIONS

Reduced magnitude and slow latency of 22q11DS subjects' responses suggest reduced central nervous system and neuronal responsiveness. These findings are consistent with significant cognitive impairments observed in 22q11DS subjects. Further research is needed to untangle the connections among basic neurotransmission dysfunction, psychophysiological responsiveness, and cognitive impairment.

Evidence from comprehensive independent validation studies for smooth pursuit dysfunction as a sensorimotor biomarker for psychosis

Smooth pursuit eye movements are considered a well-established and quantifiable biomarker of sensorimotor function in psychosis research. Identifying psychotic syndromes on an individual level based on neurobiological markers is limited by heterogeneity and requires comprehensive external validation to avoid overestimation of prediction models. Here, we studied quantifiable sensorimotor measures derived from smooth pursuit eye movements in a large sample of psychosis probands (N = 674) and healthy controls (N = 305) using multivariate pattern analysis. Balanced accuracies of 64% for the prediction of psychosis status are in line with recent results from other large heterogenous psychiatric samples. They are confirmed by external validation in independent large samples including probands with (1) psychosis (N = 727) versus healthy controls (N = 292), (2) psychotic (N = 49) and non-psychotic bipolar disorder (N = 36), and (3) non-psychotic affective disorders (N = 119) and psychosis (N = 51) yielding accuracies of 65%, 66% and 58%, respectively, albeit slightly different psychosis syndromes. Our findings make a significant contribution to the identification of biologically defined profiles of heterogeneous psychosis syndromes on an individual level underlining the impact of sensorimotor dysfunction in psychosis.

Different levels of prepulse inhibition among patients with first-episode schizophrenia, bipolar disorder and major depressive disorder

BACKGROUND

Deficits in prepulse inhibition may be a common feature in first-episode schizophrenia, bipolar disorder (BD) and major depressive disorder (MDD). We sought to explore the levels and viability of prepulse inhibition to differentiate first-episode schizophrenia, BD and MDD in patient populations.

METHODS

We tested patients with first-episode schizophrenia, BD or MDD and healthy controls using prepulse inhibition paradigms, namely perceived spatial co-location (PSC-PPI) and perceived spatial separation (PSS-PPI).

RESULTS

We included 53 patients with first-episode schizophrenia, 30 with BD and 25 with MDD, as well as 82 healthy controls. The PSS-PPI indicated that the levels of prepulse inhibition were smallest to largest, respectively, in the first-episode schizophrenia, BD, MDD and control groups. Relative to the healthy controls, the prepulse inhibition deficits in the first-episode schizophrenia group were significant (p < 0.001), but the prepulse inhibitions were similar between patients with BD and healthy controls, and between patients with MDD and healthy controls. The receiver operating characteristic curve analysis showed that PSS-PPI (area under the curve [AUC] 0.73, p < 0.001) and latency (AUC 0.72, p < 0.001) were significant for differentiating patients with first-episode schizophrenia or BD from healthy controls.

LIMITATIONS

The demographics of the 4 groups were not ideally matched. We did not perform cognitive assessments. The possible confounding effect of medications on prepulse inhibition could not be eliminated.

CONCLUSION

The level of prepulse inhibition among patients with first-episode schizophrenia was the lowest, with levels among patients with BD, patients with MDD and healthy controls increasingly higher. The PSS-PPI paradigm was more effective than PSC-PPI to recognize deficits in prepulse inhibition. These results provide a basis for further research on biological indicators that can assist differential diagnoses in psychosis.

Prepulse inhibition deficit as a transdiagnostic process in neuropsychiatric disorders: a systematic review

BACKGROUND

Psychopathological research is moving from a specific approach towards transdiagnosis through the analysis of processes that appear transversally to multiple pathologies. A phenomenon disrupted in several disorders is prepulse inhibition (PPI) of the startle response, in which startle to an intense sensory stimulus, or pulse, is reduced if a weak stimulus, or prepulse, is previously presented.

OBJECTIVE AND METHODS

The present systematic review analyzed the role of PPI deficit as a possible transdiagnostic process for four main groups of neuropsychiatric disorders: (1) trauma-, stress-, and anxiety-related disorders (2) mood-related disorders, (3) neurocognitive disorders, and (4) other disorders such as obsessive-compulsive, tic-related, and substance use disorders. We used Web of Science, PubMed and PsycInfo databases to search for experimental case-control articles that were analyzed both qualitatively and based on their potential risk of bias. A total of 64 studies were included in this systematic review. Protocol was submitted prospectively to PROSPERO 04/30/2022 (CRD42022322031).

RESULTS AND CONCLUSION

The results showed a general PPI deficit in the diagnostic groups mentioned, with associated deficits in the dopaminergic neurotransmission system, several areas implied such as the medial prefrontal cortex or the amygdala, and related variables such as cognitive deficits and anxiety symptoms. It can be concluded that the PPI deficit appears across most of the neuropsychiatric disorders examined, and it could be considered as a relevant measure in translational research for the early detection of such disorders.

Eye Movement Abnormalities Can Distinguish First-Episode Schizophrenia, Chronic Schizophrenia, and Prodromal Patients From Healthy Controls

Background

This study attempts to replicate in a Chinese population an earlier UK report that eye movement abnormalities can accurately distinguish schizophrenia (SCZ) cases from healthy controls (HCs). It also seeks to determine whether first-episode SCZ differ from chronic SCZ and whether these eye movement abnormalities are enriched in psychosis risk syndrome (PRS).

Methods

The training set included 104 Chinese HC and 60 Chinese patients with SCZ, and the testing set included 20 SCZ patients and 20 HC from a UK cohort. An additional 16 individuals with PRS were also enrolled. Eye movements of all participants were recorded during free-viewing, smooth pursuit, and fixation stability tasks. Group differences in 55 performance measures were compared and a gradient-boosted decision tree model was built for predictive analyses.

Results

Extensive eye-movement abnormalities were observed in patients with SCZ on almost all eye-movement tests. On almost all individual variables, first-episode patients showed no statistically significant differences compared with chronic patients. The classification model was able to discriminate patients from controls with an area under the curve of 0.87; the model also classified 88% of PRS individuals as SCZ-like.

Conclusions

Our findings replicate and extend the UK results. The overall accuracy of the Chinese study is virtually identical to the UK findings. We conclude that eye-movement abnormalities appear early in the natural history of the disorder and can be considered as potential trait markers for SCZ diathesis.

Sensory gating is related to positive and disorganised schizotypy in contrast to smooth pursuit eye movements and latent inhibition

Since the characteristics and symptoms of both schizophrenia and schizotypy are manifested heterogeneously, it is possible that different endophenotypes and neurophysiological measures (sensory gating and smooth pursuit eye movement errors) represent different clusters of symptoms. Participants (N = 205) underwent a standard conditioned-pairing paradigm to establish their sensory gating ratio, a smooth-pursuit eye-movement task, a latent inhibition task, and completed the Schizotypal Personality Questionnaire. A Multidimensional Scaling analysis revealed that sensory gating was related to positive and disorganised dimensions of schizotypy. Latent inhibition and prepulse inhibition were not related to any dimension of schizotypy. Smooth pursuit eye movement error was unrelated to sensory gating and latent inhibition, but was related to negative dimensions of schizotypy. Our findings suggest that the symptom clusters associated with two main endophenotypes are largely independent. To fully understand symptomology and outcomes of schizotypal traits, the different subtypes of schizotypy (and potentially, schizophrenia) ought to be considered separately rather than together.

An active inference perspective on the negative symptoms of schizophrenia

Predictive coding has played a transformative role in the study of psychosis, casting delusions and hallucinations as statistical inference in a system with abnormal precision. However, the negative symptoms of schizophrenia, such as affective blunting, avolition, and asociality, remain poorly understood. We propose a computational framework for emotional expression based on active inference-namely that affective behaviours such as smiling are driven by predictions about the social consequences of smiling. Similarly to how delusions and hallucinations can be explained by predictive uncertainty in sensory circuits, negative symptoms naturally arise from uncertainty in social prediction circuits. This perspective draws on computational principles to explain blunted facial expressiveness and apathy-anhedonia in schizophrenia. Its phenomenological consequences also shed light on the content of paranoid delusions and indistinctness of self-other boundaries. Close links are highlighted between social prediction, facial affect mirroring, and the fledgling study of interoception. Advances in automated analysis of facial expressions and acoustic speech patterns will allow empirical testing of these computational models of the negative symptoms of schizophrenia.

Prepulse inhibition in first-degree relatives of schizophrenia patients: A systematic review

BACKGROUND

Prepulse inhibition (PPI) is a measure of sensorimotor gating used to identify deficits in early-stage information processing and inhibitory function defects. Many studies support the presence of PPI deficits in schizophrenia patients. However, very few studies have explored PPI levels among first-degree relatives (FDR) of schizophrenia patients, and the results have been inconsistent. This review article explored PPI levels in FDR of schizophrenia patients.

METHODS

We performed a systematic literature review using the PubMed, Cochrane, Embase, EBSCO and Chinese databases from inception to January 2020. A series of related factors (eg, PPI paradigm, heritability and sample characteristics) and outcomes were summarized from the literature that met the inclusion criteria. The Newcastle-Ottawa Scale was used to assess the quality of the included studies.

RESULTS

A total of eight studies were eligible for systematic review after screening. A meta-analysis of the selected studies was not conducted due to the limitations of quantity and paradigm heterogeneity. A majority of the studies' subjects were siblings of schizophrenia patients and different paradigms were applied. Most of the included studies reported no difference in PPI values between FDR of schizophrenia patients and healthy controls.

CONCLUSION

Contrary to traditional certainty that unaffected FDR of schizophrenia patients have PPI defects, our review found no sufficient evidence supporting that the PPI level in FDR of schizophrenia patients was lower than in healthy controls. A prospective cohort study focusing on different outcomes such as developing schizophrenia is required to explore PPI levels in FDR of schizophrenia patients.

Functional connectivity during smooth pursuit eye movements

Smooth pursuit eye movements (SPEM) hold the image of a slowly moving stimulus on the fovea. The neural system underlying SPEM primarily includes visual, parietal, and frontal areas. In the present study, we investigated how these areas are functionally coupled and how these couplings are influenced by target motion frequency. To this end, healthy participants (n = 57) were instructed to follow a sinusoidal target stimulus moving horizontally at two different frequencies (0.2 Hz, 0.4 Hz). Eye movements and blood oxygen level-dependent (BOLD) activity were recorded simultaneously. Functional connectivity of the key areas of the SPEM network was investigated with a psychophysiological interaction (PPI) approach. How activity in five eye movement-related seed regions (lateral geniculate nucleus, V1, V5, posterior parietal cortex, frontal eye fields) relates to activity in other parts of the brain during SPEM was analyzed. The behavioral results showed clear deterioration of SPEM performance at higher target frequency. BOLD activity during SPEM versus fixation occurred in a geniculo-occipito-parieto-frontal network, replicating previous findings. PPI analysis yielded widespread, partially overlapping networks. In particular, frontal eye fields and posterior parietal cortex showed task-dependent connectivity to large parts of the entire cortex, whereas other seed regions demonstrated more regionally focused connectivity. Higher target frequency was associated with stronger activations in visual areas but had no effect on functional connectivity. In summary, the results confirm and extend previous knowledge regarding the neural mechanisms underlying SPEM and provide a valuable basis for further investigations such as in patients with SPEM impairments and known alterations in brain connectivity.NEW & NOTEWORTHY This study provides a comprehensive investigation of blood oxygen level-dependent (BOLD) functional connectivity during smooth pursuit eye movements. Results from a large sample of healthy participants suggest that key oculomotor regions interact closely with each other but also with regions not primarily associated with eye movements. Understanding functional connectivity during smooth pursuit is important, given its potential role as an endophenotype of psychoses.

Meta-Analysis of Sensorimotor Gating Deficits in Patients With Schizophrenia Evaluated by Prepulse Inhibition Test

Prepulse inhibition (PPI) of startle is an operational measure of sensorimotor gating that is often impaired in patients with schizophrenia. Despite the large number of studies, there is considerable variation in PPI outcomes reported. We conducted a systematic review and meta-analysis investigating PPI impairment in patients with schizophrenia compared with healthy control subjects, and examined possible explanations for the variation in results between studies. Major databases were screened for observational studies comparing healthy subjects and patients with schizophrenia for the prepulse and pulse intervals of 60 and 120 ms as primary outcomes, ie, PPI-60 and PPI-120. Standardized mean difference (SMD) and 95% confidence intervals (CI) were extracted and pooled using random effects models. We then estimated the mean effect size of these measures with random effects meta-analyses and evaluated potential PPI heterogeneity moderators, using sensitivity analysis and meta-regressions. Sixty-seven primary studies were identified, with 3685 healthy and 4290 patients with schizophrenia. The schizophrenia group showed reduction in sensorimotor gating for both PPI-60 (SMD = -0.50, 95% CI = [-0.61, -0.39]) and PPI-120 (SMD = -0.44, 95% CI = [-0.54, -0.33]). The sensitivity and meta-regression analysis showed that sample size, gender proportion, imbalance for gender, source of control group, and study continent were sources of heterogeneity (P < .05) for both PPI-60 and PPI-120 outcomes. Our findings confirm a global sensorimotor gating deficit in schizophrenia patients, with overall moderate effect size for PPI-60 and PPI-120. Methodological consistency should decrease the high level of heterogeneity of PPI results between studies.

Cognitive Impairment and Diminished Neural Responses Constitute a Biomarker Signature of Negative Symptoms in Psychosis

The treatment of negative symptoms (NS) in psychosis represents an urgent unmet medical need given the significant functional impairment it contributes to psychosis syndromes. The lack of progress in treating NS is impacted by the lack of known pathophysiology or associated quantitative biomarkers, which could provide tools for research. This current analysis investigated potential associations between NS and an extensive battery of behavioral and brain-based biomarkers in 932 psychosis probands from the B-SNIP database. The current analyses examined associations between PANSS-defined NS and (1) cognition, (2) pro-/anti-saccades, (3) evoked and resting-state electroencephalography (EEG), (4) resting-state fMRI, and (5) tractography. Canonical correlation analyses yielded symptom-biomarker constructs separately for each biomarker modality. Biomarker modalities were integrated using canonical discriminant analysis to summarize the symptom-biomarker relationships into a "biomarker signature" for NS. Finally, distinct biomarker profiles for 2 NS domains ("diminished expression" vs "avolition/apathy") were computed using step-wise linear regression. NS were associated with cognitive impairment, diminished EEG response amplitudes, deviant resting-state activity, and oculomotor abnormalities. While a connection between NS and poor cognition has been established, association to neurophysiology is novel, suggesting directions for future mechanistic studies. Each biomarker modality was related to NS in distinct and complex ways, giving NS a rich, interconnected fingerprint and suggesting that any one biomarker modality may not adequately capture the full spectrum of symptomology.

Smooth pursuit eye movement deficits as a biomarker for psychotic features in bipolar disorder-Findings from the PARDIP study

OBJECTIVES

Smooth pursuit eye movement deficits are an established psychosis biomarker across schizophrenia, schizoaffective and psychotic bipolar disorder (BPwP). Whether smooth pursuit deficits are also seen in bipolar disorder without psychosis (BPwoP) is unclear. Here we present data from the Psychosis and Affective Research Domains and Intermediate Phenotypes (PARDIP) study comparing bipolar patients with and without psychotic features.

METHODS

Probands with BPwP (N = 49) and BPwoP (N = 36), and healthy controls (HC, N = 71) performed eye tracking tasks designed to evaluate specific sensorimotor components relevant for pursuit initiation and pursuit maintenance.

RESULTS

While BPwoP did not differ from either BPwP or HC on initial eye acceleration, they performed significantly better than BPwP on early (P < .01) and predictive (P = .02) pursuit maintenance measures, both without differing from HC. BPwP were impaired compared to HC on initial eye acceleration, and on early and predictive pursuit maintenance (all P < .01). In contrast to the three pursuit measures, BPwP and BPwoP were both impaired on general neurocognitive assessments in relation to HC (both P < .001), without a significant difference between the two bipolar patient groups.

CONCLUSIONS

Our findings support the model that impairments of sensorimotor and cognitive processing as required for early and later predictive smooth pursuit maintenance are relatively specific to those bipolar patients with a history of psychosis. This suggests that the neural circuitry for developing feed-forward predictive models for accurate pursuit maintenance is associated with the occurrence of psychotic features in bipolar patients. In contrast, generalized neuropsychological impairments did not differentiate the two bipolar patient groups.

Lower prepulse inhibition in clinical high-risk groups but not in familial risk groups for psychosis compared with healthy controls

AIM

Although the lower level of prepulse inhibition (PPI) of the startle response is well known in schizophrenia, the onset of this difference is not clear. The aim of the present study was to compare PPI in individuals with clinical and familial high risk for psychosis, and healthy controls.

METHODS

We studied PPI in individuals within three groups: ultra-high risk for psychosis (UHR, n = 29), familial high risk for psychosis (FHR, n = 24) and healthy controls (HC, n = 28). The FHR group was chosen among siblings of patients with schizophrenia, whereas UHR was defined based on the Comprehensive Assessment of At-Risk Mental States (CAARMS). We collected clinical data using the BPRS-E, SANS and SAPS when individuals with UHR were antipsychotic-naïve. A cognitive battery that assessed attention, cognitive flexibility, working memory, verbal learning and memory domains was applied to all participants.

RESULTS

PPI was lower in the UHR group compared with both the FHR and HC groups. Those with a positive family history for schizophrenia had lower PPI than others in the UHR group. There was no difference in PPI between the FHR and HC groups. We found no relationship between PPI and cognitive performance in the three groups. Startle reactivity was not different among the three groups. Positive and negative symptoms were not related to PPI and startle reactivity in the UHR group.

CONCLUSIONS

Our findings suggest that clinical and familial high-risk groups for psychosis have different patterns of PPI.

Relationship of prolonged acoustic startle latency to diagnosis and biotype in the bipolar-schizophrenia network on intermediate phenotypes (B-SNIP) cohort

BACKGROUND

Latency of the acoustic startle reflex is the time from presentation of the startling stimulus until the response and provides an index of neural processing speed. Latency is prolonged in schizophrenia, is 90% heritable, and predicts conversion to schizophrenia in a high-risk population. The Bipolar-Schizophrenia Network for Intermediate Phenotypes (B-SNIP) consortium investigates neurobiological features found in psychotic disorders spanning diagnostic criteria for schizophrenia (SCZ), schizoaffective disorder (SAD), and psychotic bipolar disorder (BP). We investigated whether differences in startle latency and prepulse inhibition (PPI) occur in probands, their first-degree relatives, and neurobiologically defined subgroups of the probands (Biotypes).

METHODS

1143 subjects were included from the B-SNIP cohort: 143 with SCZ, 178 SCZ relatives (SCZ-Fam), 123 with SAD, 152 SAD relatives (SAD-Fam), 138 BP, 183 BP relatives (BP-Fam), and 226 controls (CON). A Biopac system recorded the eyeblink component of the startle reflex during startle testing.

RESULTS

Latency differed by diagnosis (F(3,620) = 5.10, p = 0.002): SCZ, SAD, and BP probands had slower latency than CON, with relatives intermediate. Biotypes 1 and 2 had slower latency than CON (p < 0.031) but Biotype 3 did not differ from CON. PPI did not separate CON from other subjects when analyzed by diagnoses nor when analyzed by biotype. Biotype 1 relatives had slower latency (F(3,663) = 3.49, p = 0.016) and more impaired PPI than Biotype 2 and 3 relatives (F(3,663) = 2.77, p = 0.041).

CONCLUSION

Startle latency is prolonged in psychotic disorders that cross traditional diagnostic categories. These data suggest a genetic difference between biotypes that span across clinically defined diagnoses.

Mechanisms of smooth pursuit eye movements in schizotypy

Several studies suggest that highly schizotypal individuals display a deficit in smooth pursuit eye movements (SPEM), which are considered an important biomarker of schizophrenia. In schizophrenia, abnormal SPEM is thought to be driven by impairments in motion perception. In schizotypy, the processes underlying reduced SPEM performance have not been examined so far, and there are no studies on motion perception deficits in schizotypy. Thus, in this registered report, we aimed to investigate whether motion perception is impaired in highly schizotypal individuals, and how it contributes to SPEM performance. On an exploratory basis, we were interested in the association between schizotypy and prediction, another mechanism underlying SPEM. To address this issue, participants with high total scores of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE short form) and control participants with low scores (N = 86 in each group) performed a standard sinusoidal SPEM task, random dot kinematograms to measure motion perception, and a blanking SPEM task to assess prediction abilities. Group comparisons as well as mediator analyses were carried out to identify whether motion perception or prediction are responsible for SPEM performance in schizotypy. We found reduced blanking SPEM performance in schizotypes compared to controls, but no group differences regarding sinusoidal SPEM and motion perception. Although no significant mediators were identified for SPEM performance in schizotypes, an exploratory analysis revealed an association between motion perception and SPEM gain in high, but not in low schizotypy. Our findings imply that despite the schizotypy-related impairment in prediction, motion perception seems to be a more important predictor of SPEM performance in schizotypes. A deficit in prediction that does not relate to SPEM performance suggests that protective factors (e.g., other cognitive processes) might operate in schizotypal individuals to maintain SPEM performance on a healthy level.

Prepulse inhibition in patients with bipolar disorder: a systematic review and meta-analysis

BACKGROUND

Prepulse inhibition (PPI) is a measurement method for the sensory gating process, which helps the brain adapt to complex environments. PPI may be reduced in patients with bipolar disorder (BD). This study investigated PPI deficits in BD and pooled the effect size of PPI in patients with BD.

METHODS

We conducted a literature search on PPI in patients with BD from inception to July 27, 2019 in PubMed, Embase, Cochrane Library databases, and Chinese databases. No age, sex, and language restriction were set. The calculation formula was PPI = 100 - [100*((prepulse - pulse amplitude) / pulse amplitude)]. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of studies.

RESULTS

Ten eligible papers were identified, of which five studies including a total of 141 euthymic patients and 132 healthy controls (HC) were included in the meta-analysis. Compared with HC, euthymic patients with BD had significantly lower PPI at the 60 ms interstimulus interval (ISI) between pulse and prepulse (P = 0.476, I2 = 0.0%, SMD = - 0.32, 95% CI = - 0.54 - -0.10). Sensitivity analysis shows no significant change in the combined effect value after removing any single study. There was no publication bias using the Egger's test at 60 ms (P = 0.606). The meta-analysis of PPI at the 60 ms ISI could have significant clinical heterogeneity in mood episode state, as well as lack of data on BD I or II subtypes.

CONCLUSIONS

Euthymic patients with BD show PPI deficits at the 60 ms, suggesting a deficit in the early sensory gate underlying PPI. The PPI inhibition rate at a 60 ms interval is a stable index. More research is needed in the future to confirm this outcome, and to delve deeper into the mechanisms behind deficits.

Disrupted Corollary Discharge in Schizophrenia: Evidence From the Oculomotor System

Corollary discharge (CD) signals are motor-related signals that exert an influence on sensory processing. They allow mobile organisms to predict the sensory consequences of their imminent actions. Among the many functions of CD is to provide a means by which we can distinguish sensory experiences caused by our own actions from those with external causes. In this way, they contribute to a subjective sense of agency. A disruption in the sense of agency is central to many of the clinical symptoms of schizophrenia, and abnormalities in CD signaling have been theorized to underpin particularly those agency-related psychotic symptoms of the illness. Characterizing abnormal CD associated with eye movements in schizophrenia and their resulting influence on visual processing and subsequent action plans may have advantages over other sensory and motor systems. That is because the most robust psychophysiological and neurophysiological data regarding the dynamics and influence of CD as well as the neural circuitry implicated in CD generation and transmission comes from the study of eye movements in humans and nonhuman primates. We review studies of oculomotor CD signaling in the schizophrenia spectrum and possible neurobiological correlates of CD disturbances. We conclude by speculating on the ways in which oculomotor CD dysfunction, specifically, may invoke specific experiences, clinical symptoms, and cognitive impairments. These speculations lay the groundwork for empirical study, and we conclude by outlining potentially fruitful research directions.

Schizotypy and smooth pursuit eye movements as potential endophenotypes of obsessive-compulsive disorder

Patients with obsessive-compulsive disorder (OCD) show dysfunctions of the fronto-striatal circuitry, which imply corresponding oculomotor deficits including smooth pursuit eye movements (SPEM). However, evidence for a deficit in SPEM is inconclusive, with some studies reporting reduced velocity gain while others did not find any SPEM dysfunctions in OCD patients. Interestingly, psychosis-like traits have repeatedly been linked to both OCD and impaired SPEM. Here, we examined a large sample of n = 168 patients with OCD, n = 93 unaffected first-degree relatives and n = 171 healthy control subjects to investigate whether elevated levels of schizotypy and SPEM deficits represent potential endophenotypes of OCD. We applied a SPEM task with high demands on predictive pursuit that is more sensitive to assess executive dysfunctions than a standard task with continuous visual feedback, as episodes of target blanking put increased demands on basal ganglia and prefrontal involvement. Additionally, we examined the relation between schizotypy and SPEM performance in OCD patients and their relatives. Results indicate that OCD patients and unaffected relatives do not show deficient performance in either standard or predictive SPEM. Yet, both patients and relatives exhibited elevated levels of schizotypy, and schizotypy was significantly correlated with velocity gain during standard trials in unmedicated and depression-free OCD patients. These findings highlight the role of schizotypy as a candidate endophenotype of OCD and add to the growing evidence for predisposing personality traits in OCD. Furthermore, intact gain may represent a key characteristic that distinguishes the OCD and schizophrenia patient populations.

Application of eye trackers for understanding mental disorders: Cases for schizophrenia and autism spectrum disorder

Studies of eye movement have become an essential tool of basic neuroscience research. Measures of eye movement have been applied to higher brain functions such as cognition, social behavior, and higher‐level decision‐making. With the development of eye trackers, a growing body of research has described eye movements in relation to mental disorders, reporting that the basic oculomotor properties of patients with mental disorders differ from those of healthy controls. Using discrimination analysis, several independent research groups have used eye movements to differentiate patients with schizophrenia from a mixed population of patients and controls. Recently, in addition to traditional oculomotor measures, several new techniques have been applied to measure and analyze eye movement data. One research group investigated eye movements in relation to the risk of autism spectrum disorder several years prior to the emergence of verbal‐behavioral abnormalities. Research on eye movement in humans in social communication is therefore considered important, but has not been well explored. Since eye movement patterns vary between patients with mental disorders and healthy controls, it is necessary to collect a large amount of eye movement data from various populations and age groups. The application of eye trackers in the clinical setting could contribute to the early treatment of mental disorders.

Studies of eye movement have become an essential tool of basic neuroscience research. With the development of eye trackers, a growing body of research has described eye movements in relation to mental disorders.

Deficits of perceived spatial separation-induced prepulse inhibition in patients with bipolar disorder compared to healthy controls

OBJECTIVE

This study aimed to assess sensorimotor gating deficits in patients with bipolar disorder (BD) using a modified perceived spatial separation-induced prepulse inhibition (PSS-PPI) paradigm. The relationships between PSS-PPI, demographic and clinical characteristics, and cognitive functioning were also analyzed.

METHODS

In this cross-sectional study, 30 patients with BD were compared to 33 healthy controls (HC) with respect to prepulse inhibition measures of PSS-PPI using a 120 ms lead interval. The Young Mania Rating Scale, Hamilton Depression Scale, and Hamilton Anxiety Scale were used to assess manic, depressive, and anxiety symptoms. Cognition was evaluated using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Stroop color-word test.

RESULTS

Compared with HC, patients with BD had a lower PSS-PPI level. PSS-PPI showed medium effect size (ES) between patients with BD and HC (ES = 0.65). Among patients with BD, PSS-PPI was positively correlated with the language domain of RBANS and negatively correlated with double word time and color interference time. There were no differences in PSS-PPI levels between patients with and without psychotic symptoms or between those euthymic patients or depressive patients with BD.

CONCLUSIONS

Patients with BD show a sensorimotor gating deficit as measured by perceived spatial separation-induced PPI of the startle response, which was more sensitive compared to the classic PPI paradigm. Euthymic bipolar patients and depressive bipolar patients show similar PPI level. PPI deficit in patients with BD is related to cognition, but not with demographic and clinical characteristics.

Correlations between exploratory eye movement, hallucination, and cortical gray matter volume in people with schizophrenia

BACKGROUND

Widespread cortical gray matter alternations in people with schizophrenia are correlated with both psychotic symptoms and cognitive/behavioral abnormalities, including the impairments of exploratory eye movement (EEM). Particularly, the loss of gray matter density is specifically related to deficits of the responsive search score (RSS) of EEM in schizophrenia. It is unknown, however, whether the schizophrenia-related RSS deficits are associated with certain psychotic symptoms, such as hallucinations.

METHODS

In 33 participants with schizophrenia, the measurement of EEM, assessment of the hallucination severity using Positive and Negative Syndrome Scale (PANSS) and a voxel-based morphometric analysis of cortical gray matter volume (GMV) were conducted to investigate the relationships between the RSS of EEM, symptom severity, and GMV. In 29 matched healthy controls, the measurement of EEM and a voxel-based morphometric analysis of cortical GMV were also conducted to investigate the relationship between the RSS of EEM and GMV.

RESULTS

In participants with schizophrenia, the hallucination severity was significantly negatively correlated with both the RSS and the GMV of a large number of brain regions in the frontal, temporal, parietal, orbitofrontal, calcarine, cingulate, and insular cortices, and rolandic operculum, hippocampus, parahippocampal gyrus, and thalamus. Also in participants with schizophrenia, the RSS was significantly positively correlated with the GMV in the left supplementary motor area (SMA), left superior frontal cortex (SFG), bilateral precentral gyri, bilateral postcentral gyri, and bilateral middle frontal cortices. More importantly, the GMV of the SMA, SFG, and precentral gyrus in the left hemisphere was not only significantly negatively correlated with the hallucination severity but also significantly positively correlated with the RSS. No significant correlation could be revealed between the RSS and the GMV of any brain regions in healthy controls.

CONCLUSIONS

There was a significantly negative association between the hallucination severity and the RSS of EEM, suggesting that the RSS may be a potential biomarker for predicting the hallucination severity of schizophrenia. Also, the GMV of the left SMA, SFG, and precentral gyrus may be the common substrates underlying both hallucination induction and the RSS in people with schizophrenia.

Genome-wide association studies of smooth pursuit and antisaccade eye movements in psychotic disorders: findings from the B-SNIP study

Eye movement deviations, particularly deficits of initial sensorimotor processing and sustained pursuit maintenance, and antisaccade inhibition errors, are established intermediate phenotypes for psychotic disorders. We here studied eye movement measures of 849 participants from the Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) study (schizophrenia N=230, schizoaffective disorder N=155, psychotic bipolar disorder N=206 and healthy controls N=258) as quantitative phenotypes in relation to genetic data, while controlling for genetically derived ancestry measures, age and sex. A mixed-modeling genome-wide association studies approach was used including ~4.4 million genotypes (PsychChip and 1000 Genomes imputation). Across participants, sensorimotor processing at pursuit initiation was significantly associated with a single nucleotide polymorphism in IPO8 (12p11.21, P=8 × 10-11), whereas suggestive associations with sustained pursuit maintenance were identified with SNPs in SH3GL2 (9p22.2, P=3 × 10-8). In participants of predominantly African ancestry, sensorimotor processing was also significantly associated with SNPs in PCDH12 (5q31.3, P=1.6 × 10-10), and suggestive associations were observed with NRSN1 (6p22.3, P=5.4 × 10-8) and LMO7 (13q22.2, P=7.3x10-8), whereas antisaccade error rate was significantly associated with a non-coding region at chromosome 7 (P=6.5 × 10-9). Exploratory pathway analyses revealed associations with nervous system development and function for 40 top genes with sensorimotor processing and pursuit maintenance (P=4.9 × 10-2-9.8 × 10-4). Our findings suggest novel patterns of genetic variation relevant for brain systems subserving eye movement control known to be impaired in psychotic disorders. They include genes involved in nuclear trafficking and gene silencing (IPO8), fast axonal guidance and synaptic specificity (PCDH12), transduction of nerve signals (NRSN1), retinal degeneration (LMO7), synaptic glutamate release (SH3GL2), and broader nervous system development and function.

The Pioneering Contributions of Irving Gottesman: An Appreciation

Irving Gottesman was one of the leading psychopathologists and behavior geneticists of our time, greatly influencing our basic conceptualization of the transmission of schizophrenia and other major mental disorders in ways that impacted research programs around the world. Here we highlight his landmark twin studies of schizophrenia, his introduction of the concept of endophenotypes, and his role in providing the conceptual base for vulnerability/stress models of schizophrenia. His ability to influence our basic assumptions about the nature of genetic factors, environmental factors, and their interaction in the onset and course of major mental disorders was truly remarkable.

Evidence that eye-movement profiles do not explain slow binocular rivalry rate in bipolar disorder: support for a perceptual endophenotype

OBJECTIVES

Presenting conflicting images simultaneously, one to each eye, produces perceptual alternations known as binocular rivalry (BR). Slow BR rate has been proposed as an endophenotype for bipolar disorder (BD) for use in large-scale genome-wide association studies. However, the trait could conceivably reflect eye movement (EM) dysfunction in BD rather than anomalous perceptual processing per se. To address this question, we examined the relationship between EM profiles and BR rate for various stimulus types in BD and healthy subjects. We also examined differences in EM profiles between these groups.

METHODS

Employing a repeated-measures within-subjects design, 20 BD outpatients and 20 age- and sex-matched healthy controls completed EM tasks and separate BR tasks involving a range of stimuli with different drift speeds. The association between each EM measure and BR rate was examined with correlational analyses for all stimulus conditions in both groups. Between-group comparisons were performed to determine any differences in those EM measures. Corresponding Bayesian analyses were also conducted.

RESULTS

There were no EM measures that showed a significant relationship with BR rate in either the BD group or the healthy group (P≥7.87×10^-3 ), where those EM measures were also significantly different between the BD and healthy groups (P≥1.32 × 10^-2 ). These findings were verified with Bayes factors.

CONCLUSIONS

The results provide evidence that EM profiles do not explain the slow BR endophenotype for BD, thus indicating that the trait reflects anomalous perceptual processing per se. This perceptual trait can be employed in clinical, genetic, mechanistic and pathophysiological studies.

Human iPSC Glial Mouse Chimeras Reveal Glial Contributions to Schizophrenia

In this study, we investigated whether intrinsic glial dysfunction contributes to the pathogenesis of schizophrenia (SCZ). Our approach was to establish humanized glial chimeric mice using glial progenitor cells (GPCs) produced from induced pluripotent stem cells derived from patients with childhood-onset SCZ. After neonatal implantation into myelin-deficient shiverer mice, SCZ GPCs showed premature migration into the cortex, leading to reduced white matter expansion and hypomyelination relative to controls. The SCZ glial chimeras also showed delayed astrocytic differentiation and abnormal astrocytic morphologies. When established in myelin wild-type hosts, SCZ glial mice showed reduced prepulse inhibition and abnormal behavior, including excessive anxiety, antisocial traits, and disturbed sleep. RNA-seq of cultured SCZ human glial progenitor cells (hGPCs) revealed disrupted glial differentiation-associated and synaptic gene expression, indicating that glial pathology was cell autonomous. Our data therefore suggest a causal role for impaired glial maturation in the development of schizophrenia and provide a humanized model for its in vivo assessment.

Combining two model systems of psychosis: The effects of schizotypy and sleep deprivation on oculomotor control and psychotomimetic states

Model systems of psychosis, such as schizotypy or sleep deprivation, are valuable in informing our understanding of the etiology of the disorder and aiding the development of new treatments. Schizophrenia patients, high schizotypes, and sleep-deprived subjects are known to share deficits in oculomotor biomarkers. Here, we aimed to further validate the schizotypy and sleep deprivation models and investigated, for the first time, their interactive effects on smooth pursuit eye movements (SPEM), prosaccades, antisaccades, predictive saccades, and measures of psychotomimetic states, anxiety, depression, and stress. To do so, n = 19 controls and n = 17 high positive schizotypes were examined after both a normal sleep night and 24 h of sleep deprivation. Schizotypes displayed higher SPEM global position error, catch-up saccade amplitude, and increased psychotomimetic states. Sleep deprivation impaired SPEM, prosaccade, antisaccade, and predictive saccade performance and increased levels of psychotomimetic experiences. Additionally, sleep deprivation reduced SPEM gain in schizotypes but not controls. We conclude that oculomotor impairments are observed in relation to schizotypy and following sleep deprivation, supporting their utility as biomarkers in model systems of psychosis. The combination of these models with oculomotor biomarkers may be particularly fruitful in assisting the development of new antipsychotic or pro-cognitive drugs.

Oculomotor Prediction: A Window into the Psychotic Mind

Psychosis - an impaired contact with reality - is a hallmark of schizophrenia. Many psychotic symptoms are associated with disruptions in agency - the sense that 'I' cause my actions. A failure to predict sensory consequences of one's own actions may underlie agency disturbances. Such predictions rely on corollary discharge (CD) signals, 'copies' of movement commands sent to sensory regions prior to action execution. Here, we make a case that the oculomotor system is a promising model for understanding CD in psychosis, building on advances in our understanding of the behavioral and neurophysiological correlates of CD associated with eye movements. In this opinion article, we provide an overview of recent evidence for disturbed oculomotor CD in schizophrenia, potentially linking bizarre and disturbing psychotic experiences with basic physiological processes.

Visual and non-visual motion information processing during pursuit eye tracking in schizophrenia and bipolar disorder

Despite many reports on visual processing deficits in psychotic disorders, studies are needed on the integration of visual and non-visual components of eye movement control to improve the understanding of sensorimotor information processing in these disorders. Non-visual inputs to eye movement control include prediction of future target velocity from extrapolation of past visual target movement and anticipation of future target movements. It is unclear whether non-visual input is impaired in patients with schizophrenia. We recorded smooth pursuit eye movements in 21 patients with schizophrenia spectrum disorder, 22 patients with bipolar disorder, and 24 controls. In a foveo-fugal ramp task, the target was either continuously visible or was blanked during movement. We determined peak gain (measuring overall performance), initial eye acceleration (measuring visually driven pursuit), deceleration after target extinction (measuring prediction), eye velocity drifts before onset of target visibility (measuring anticipation), and residual gain during blanking intervals (measuring anticipation and prediction). In both patient groups, initial eye acceleration was decreased and the ability to adjust eye acceleration to increasing target acceleration was impaired. In contrast, neither deceleration nor eye drift velocity was reduced in patients, implying unimpaired non-visual contributions to pursuit drive. Disturbances of eye movement control in psychotic disorders appear to be a consequence of deficits in sensorimotor transformation rather than a pure failure in adding cognitive contributions to pursuit drive in higher-order cortical circuits. More generally, this deficit might reflect a fundamental imbalance between processing external input and acting according to internal preferences.

Prepulse inhibition in euthymic bipolar disorder patients in comparison with control subjects

OBJECTIVE

Deficient prepulse inhibition (PPI) of the startle response, indicating sensorimotor gating deficits, has been reported in schizophrenia and other neuropsychiatric disorders. This study aimed to assess sensorimotor gating deficits in patients with euthymic bipolar. Furthermore, we analysed the relationships between PPI and clinical and cognitive measures.

METHOD

Prepulse inhibition was measured in 64 patients with euthymic bipolar and in 64 control subjects matched for age, gender, education level and smoking status. Clinical characteristics and level of functioning were assessed in all participants using Hamilton Depression Rating Scale (HDRS), Young Mania Rating Scale (YMRS) and Functioning Assessment Short Test (FAST). Cognition was evaluated using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) and the Stroop test as an additional measure of executive function.

RESULTS

Compared with controls, patients with bipolar disorder exhibited PPI deficits at 60- and 120-millisecond prepulse-pulse intervals. Among patients with bipolar disorder, PPI was correlated with the social cognition domain of the MCCB. PPI was not significantly correlated with other clinical, functional and neurocognitive variables in either group.

CONCLUSIONS

Our data suggest that PPI deficit is a neurobiological marker in euthymic bipolar disorder, which is associated with social cognition but not with other clinical, functional or cognitive measures.

Consensus paper of the WFSBP Task Force on Biological Markers: Criteria for biomarkers and endophenotypes of schizophrenia part I: Neurophysiology

The neurophysiological components that have been proposed as biomarkers or as endophenotypes for schizophrenia can be measured through electroencephalography (EEG) and magnetoencephalography (MEG), transcranial magnetic stimulation (TMS), polysomnography (PSG), registration of event-related potentials (ERPs), assessment of smooth pursuit eye movements (SPEM) and antisaccade paradigms. Most of them demonstrate deficits in schizophrenia, show at least moderate stability over time and do not depend on clinical status, which means that they fulfil the criteria as valid endophenotypes for genetic studies. Deficits in cortical inhibition and plasticity measured using non-invasive brain stimulation techniques seem promising markers of outcome and prognosis. However the utility of these markers as biomarkers for predicting conversion to psychosis, response to treatments, or for tracking disease progression needs to be further studied.

Pursuit eye movements as an intermediate phenotype across psychotic disorders: Evidence from the B-SNIP study

Smooth pursuit eye tracking deficits are a promising intermediate phenotype for schizophrenia and possibly for psychotic disorders more broadly. The Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) consortium investigated the severity and familiality of different pursuit parameters across psychotic disorders. Probands with schizophrenia (N=265), schizoaffective disorder (N=178), psychotic bipolar disorder (N=231), their first-degree relatives (N=306, N=217, N=273, respectively) and healthy controls (N=305) performed pursuit tracking tasks designed to evaluate sensorimotor and cognitive/predictive aspects of pursuit. Probands from all diagnostic groups were impaired on all pursuit measures of interest compared to controls (p<0.001). Schizophrenia probands were more impaired than other proband groups on both early pursuit gain and predictive gain. Relatives with and without enhanced psychosis spectrum personality traits were impaired on initial eye acceleration, the most direct sensorimotor pursuit measure, but not on pursuit gain measures. This suggests that alterations in early sensorimotor function may track susceptibility to psychosis even in the absence of psychosis related personality traits. There were no differences in pursuit measures between relatives of the three proband groups. Familiality estimates of pursuit deficits indicate that early pursuit gain was more familial than predictive gain, which has been the most widely used measure in previous family studies of psychotic disorders. Thus, while disease-related factors may induce significant impairments of pursuit gain, especially in schizophrenia, the pattern of deficits in relatives and their familiality estimates suggest that alterations in sensorimotor function at pursuit onset may indicate increased susceptibility across psychotic disorders.

Association of chromosome 5q21.3 polymorphisms with the exploratory eye movement dysfunction in schizophrenia

Schizophrenia patients show abnormalities in many eye movement tasks. Among them, exploratory eye movements (EEM) dysfunction seems to be specific to schizophrenia. However the mechanism of EEM disturbances in schizophrenia patients remains elusive. We investigate the relationship between EEM and single nucleotide polymorphisms (SNPs) or genes to identify susceptibility loci for EEM in schizophrenia. We firstly performed EEM test, then performed a genome-wide association study (GWAS) and gene-based association study of EEM in 128 individuals with schizophrenia and 143 healthy control subjects. Comparing to healthy controls, schizophrenia patients show significant decrease in NEF (22.99 ± 3.96 vs. 26.02 ± 5.72, P <0.001), TESL (368.78 ± 123.57 vs. 603.12 ± 178.63, P <0.001), MESL (16.86 ± 5.27 vs. 24.42 ± 6.46, P <0.001), RSS (8.22 ± 1.56 vs. 10.92 ± 1.09, P <0.001), and CSS (5.06 ± 0.97 vs. 6.64 ± 0.87, P <0.001). Five SNPs of the MAN2A1, at 5q21.3, were associated with EEM abnormalities (deceased CSS) and satisfied the criteria of GWAS significance threshold. One is localized near 5'-UTR (rs17450784) and four are in intron (rs1438663, rs17162094, rs6877440 and rs10067856) of the gene. Our findings suggest that the identified loci may control the schizophrenia-related quantitative EEM trait. And the identified gene, associated with the EEM phenotype, may lead to new insights into the etiology of schizophrenia.

Modafinil effects on middle-frequency oscillatory power during rule selection in schizophrenia

Control-related cognitive processes such as rule selection are associated with cortical oscillations in the theta, alpha and, beta ranges, and modulated by catecholamine neurotransmission. Thus, a potential strategy for improving cognitive control deficits in schizophrenia would be to use pro-catecholamine pharmacological agents to augment these control-related oscillations. In a double-blind, placebo-controlled (within-subjects) study, we tested the effects of adjunctive single-dose modafinil 200 mg on rule-related 4-30 Hz oscillations in 23 stable schizophrenia patients, using EEG during cognitive control task performance. EEG data underwent time-frequency decomposition with Morlet wavelets to determine the power of 4-30 Hz oscillations. Modafinil (relative to placebo) enhanced oscillatory power associated with high-control rule selection in theta, alpha, and beta ranges, with modest effects during rule maintenance. Modafinil treatment in schizophrenia augments middle-frequency cortical oscillatory power associated with rule selection, and may subserve diverse subcomponent processes in proactive cognitive control.

Diagnostic specificity and familiality of early versus late evoked potentials to auditory paired stimuli across the schizophrenia-bipolar psychosis spectrum

Disrupted sensory processing is a core feature of psychotic disorders. Auditory paired stimuli (PS) evoke a complex neural response, but it is uncertain which aspects reflect shared and/or distinct liability for the most common severe psychoses, schizophrenia (SZ) and psychotic bipolar disorder (BDP). Evoked time-voltage/time-frequency domain responses quantified with EEG during a typical PS paradigm (S1-S2) were compared among proband groups (SZ [n = 232], BDP [181]), their relatives (SZrel [259], BDPrel [220]), and healthy participants (H [228]). Early S1-evoked responses were reduced in SZ and BDP, while later/S2 abnormalities showed SZ/SZrel and BDP/BDPrel specificity. Relatives' effects were absent/small despite significant familiality of the entire auditorineural response. This pattern suggests general and divergent biological pathways associated with psychosis, yet may reflect complications with conditioning solely on clinical phenomenology.

Deficient prepulse inhibition in schizophrenia detected by the multi-site COGS

BACKGROUND

Startle inhibition by weak prepulses (PPI) is studied to understand the biology of information processing in schizophrenia patients and healthy comparison subjects (HCS). The Consortium on the Genetics of Schizophrenia (COGS) identified associations between PPI and single nucleotide polymorphisms in schizophrenia probands and unaffected relatives, and linkage analyses extended evidence for the genetics of PPI deficits in schizophrenia in the COGS-1 family study. These findings are being extended in a 5-site "COGS-2" study of 1800 patients and 1200 unrelated HCS to facilitate genetic analyses. We describe a planned interim analysis of COGS-2 PPI data.

METHODS

Eyeblink startle was measured in carefully screened HCS and schizophrenia patients (n=1402). Planned analyses of PPI (60 ms intervals) assessed effects of diagnosis, sex and test site, PPI-modifying effects of medications and smoking, and relationships between PPI and neurocognitive measures.

RESULTS

884 subjects met strict inclusion criteria. ANOVA of PPI revealed significant effects of diagnosis (p=0.0005) and sex (p<0.002), and a significant diagnosis×test site interaction. HCS>schizophrenia PPI differences were greatest among patients not taking 2nd generation antipsychotics, and were independent of smoking status. Modest but significant relationships were detected between PPI and performance in specific neurocognitive measures.

DISCUSSION

The COGS-2 multi-site study detects schizophrenia-related PPI deficits reported in single-site studies, including patterns related to diagnosis, prepulse interval, sex, medication and other neurocognitive measures. Site differences were detected and explored. The target COGS-2 schizophrenia "endophenotype" of reduced PPI should prove valuable for identifying and confirming schizophrenia risk genes in future analyses.