BACKGROUND:Mismatch negativity (MMN) is a component of the auditory event-related potential (ERP) that is elicited during a passive oddball paradigm where task-irrelevant infrequent deviants are presented in a stream of more frequent standard stimuli. MMN is believed to index a preattentive stage of auditory information processing closely linked to NMDA receptor (NMDAR) function. Ketamine is thought to act primarily as an NMDAR antagonist, has been used in clinical trials to model the symptoms of schizophrenia, and is increasingly being used in the clinic to treat depression. Various studies have reported that ketamine reduces MMN amplitude, which in turn may reflect reduced function of NMDAR-mediated neurotransmission. Nonetheless, there is growing evidence showing MMN amplitude either having high variability or, paradoxically, moving in the opposite direction after ketamine in different individuals. METHODS:We analyzed results from 3 independent ERP studies to test the hypothesis of a crossover interaction (disordinal drug effect) between the duration-deviant MMN amplitude at baseline (without ketamine) and the direction and magnitude of the ketamine effect. To rule out regression to the mean (RTM), a statistical phenomenon that may also partially explain this crossover interaction, we separately estimated RTM using a drug-free test-retest study. RESULTS:Our results are the first to statistically demonstrate the existence of a disordinal drug response to ketamine, where the direction and magnitude of ketamine-induced changes in MMN amplitude can be predicted by baseline MMN amplitude. CONCLUSIONS:These new insights may contribute to novel precision medicine approaches in the treatment of central nervous system disorders.

BACKGROUND: Auditory steady-state response (ASSR) abnormalities in the 40-Hz (gamma band) frequency have been observed in schizophrenia and in rodent studies of NMDA receptor (NMDAR) hypofunction. However, the extent to which 40-Hz ASSR abnormalities in schizophrenia resemble deficits in 40-Hz ASSR induced by acute administration of ketamine, an NMDAR antagonist, is not yet known. METHODS: To address this knowledge gap, we conducted parallel electroencephalography studies: a crossover, placebo-controlled ketamine drug challenge study with healthy participants (study 1) and a comparison of patients with schizophrenia and healthy control participants (study 2). Time-frequency analysis of the ASSR was used to calculate baseline, broadband gamma power, evoked power, total power, phase-locking factor, and phase-locking angle. RESULTS: Relative to healthy control participants, patients with schizophrenia exhibited increases in prestimulus broadband gamma power and reductions in 40-Hz ASSR evoked power, total power, and phase-locking factor, replicating previous studies. However, we failed to replicate previous findings of 40-Hz ASSR phase delay in schizophrenia. Relative to placebo, ketamine increased prestimulus broadband gamma power; reduced 40-Hz ASSR evoked power, total power, and phase-locking factor; and advanced the phase of the 40-Hz ASSR. CONCLUSIONS: Normalized by their respective control groups/conditions, direct comparison of these measures between schizophrenia and ketamine data only revealed significant differences in phase, supporting the role of NMDAR hypofunction in mediating gamma oscillation abnormalities in schizophrenia.

Individuals at clinical high risk for psychosis (CHR) have variable clinical outcomes and low conversion rates, limiting development of novel and personalized treatments. Moreover, given risks of antipsychotic drugs, safer effective medications for CHR individuals are needed. The Accelerating Medicines Partnership® Schizophrenia (AMP® SCZ) Program was launched to address this need. Based on past CHR and schizophrenia studies, AMP SCZ assessed electroencephalography (EEG)-based event-related potential (ERP), event-related oscillation (ERO), and resting EEG power spectral density (PSD) measures, including mismatch negativity (MMN), auditory and visual P300 to target (P3b) and novel (P3a) stimuli, 40-Hz auditory steady state response, and resting EEG PSD for traditional frequency bands (eyes open/closed). Here, in an interim analysis of AMP SCZ EEG measures, we assess test-retest reliability and stability over sessions (baseline, month-2 follow-up) in CHR (n = 654) and community control (CON; n = 87) participants. Reliability was calculated as Generalizability (G)-coefficients, and changes over session were assessed with paired t-tests. G-coefficients were generally good to excellent in both groups (CHR: mean = 0.72, range = 0.49–0.85; CON: mean = 0.71, range = 0.44–0.89). Measure magnitudes significantly (p < 0.001) decreased over session (MMN, auditory and visual target P3b, visual novel P3a, 40-Hz ASSR) and/or over runs within sessions (MMN, auditory/visual novel P3a and target P3b), consistent with habituation effects. Despite these small systematic habituation effects, test-retest reliabilities of the AMP SCZ EEG-based measures are sufficiently strong to support their use in CHR studies as potential predictors of clinical outcomes, markers of illness progression, and/or target engagement or secondary outcome measures in controlled clinical trials. Watch Dr Daniel H. Mathalon discuss their work and this article: https://vimeo.com/1066564687 .

Background Social functioning difficulties in adolescents and young adults at clinical high risk for psychosis (CHR-P) are among the strongest risk factors for psychosis onset. Recent research in patients with schizophrenia has demonstrated complex relationships between early auditory processing deficits as measured by the mismatch negativity (MMN) response of the auditory event-related potential, neurocognition, social cognition, negative symptoms, and social functioning. However, the interrelationships of these variables and associations with social functioning impairments prior to the onset of the illness are unclear. The present study used a structural equation modeling (SEM) approach to integrate these factors to determine the specific determinants that lead to poor social functioning in CHR-P youth. Methods A total of 518 CHR-P individuals from the NAPLS2 (North American Prodrome Longitudinal Study) were used to evaluate SEMs with pathways starting from MMN to social functioning. The intervening variables included processing speed, social cognition, and negative symptoms. Results A final trimmed model revealed that early auditory processing (MMN) had a direct effect on processing speed, and both processing speed and negative symptoms had direct effects on social functioning. The direct effect from social cognition to social functioning was not significant. Conclusions Our findings suggest that neurophysiological deficits are associated with social functioning by way of processing speed impairments, which fully accounted for the relationship in CHR-P youths prior to psychosis onset. These results may have implications for early intervention strategies that target early information-processing deficits with the aim of improving social trajectories and limiting psychosis onset in young CHR-P individuals.

Background:Reduced mismatch negativity (MMN) and P300 event-related potential (ERP) components are widely replicated in schizophrenia and are also observed in individuals at clinical high risk for psychosis (CHR-P) who subsequently convert to psychosis. It is unknown whether they reflect changes in excitatory and/or inhibitory synaptic function, both implicated in schizophrenia and considered potential drug targets. Methods:We analyzed baseline MMN and P300 ERPs from the NAPLS2 study, asking whether altered synaptic excitation, inhibition, or both could explain amplitude reductions in CHR-P (n=583). CHR-P participants who converted to psychosis (CHR-Converters; n=77) or remitted by 24-month follow-up (CHR-Remitters; n=94) were compared on MMN evoked by pitch+duration double-deviant tones and P300 elicited by target tones from passive and active auditory oddball paradigms, respectively. Biophysical modeling was used to infer (excitatory) pyramidal cell and (inhibitory) interneuron function from both MMN and P300 ERPs. Results:MMN and P300 amplitude reductions in future CHR-Converters relative to CHR-Remitters were best explained by reduced pyramidal cell excitability (posterior probability P>.95 of a group-by-condition interaction effect). In simulations, reduced pyramidal cell excitability suppressed deviant and target ERPs. Within CHR-Converters, but not CHR-Remitters, more severe positive symptoms were associated with disinhibition of pyramidal cells (P>.99). Conclusions:Results mirror previous findings in schizophrenia and suggest that reduced pyramidal cell excitability is present at baseline in future CHR-Converters, supporting the hypothesis that hypofunction of pyramidal cells is a primary pathology in schizophrenia, rather than a consequence of chronic illness. Positive symptoms among CHR-Converters may reflect compensatory downregulation of inhibition.

Neuroimaging methods rely on models of neurovascular coupling that assume hemodynamic responses evolve seconds after changes in neural activity. However, emerging evidence reveals noncanonical BOLD (blood oxygen level dependent) responses that are delayed under stress and aberrant in neuropsychiatric conditions. To investigate BOLD coupling to resting-state fluctuations in neural activity, we simultaneously recorded EEG and fMRI in people with schizophrenia and psychiatrically unaffected participants. We focus on alpha band power to examine voxelwise, time-lagged BOLD correlations. Principally, we find diversity in the temporal profile of alpha-BOLD coupling within regions of the default mode network (DMN). This includes early coupling (0-2 seconds BOLD lag) for more posterior regions, thalamus and brainstem. Anterior regions of the DMN show coupling at canonical lags (4-6 seconds), with greater lag scores associated with self-reported measures of stress and greater lag scores in participants with schizophrenia. Overall, noncanonical alpha-BOLD coupling is widespread across the DMN and other non-cortical regions, and is delayed in people with schizophrenia. These findings are consistent with a hemo-neural hypothesis, that blood flow and/or metabolism can regulate ongoing neural activity, and further, that the hemo-neural lag may be associated with subjective arousal or stress. Our work highlights the need for more studies of neurovascular coupling in psychiatric conditions.

Impairments in mismatch negativity (MMN) are well-established in schizophrenia and have been observed in youth at clinical high-risk for psychosis (CHR-P). Prior animal studies have shown that social isolation may be related to neurobiological changes, including reduced MMN-like responses and schizophrenia-like behaviors. In parallel, neighborhood social fragmentation has been shown to be associated with the onset of psychosis. This study investigates the association between neighborhood social fragmentation and MMN impairment among CHR-P youth and healthy comparisons (HC). Data were collected from the North American Prodrome Longitudinal Study Phase 2. Electroencephalography was recorded during an unattended auditory oddball paradigm with duration-, pitch-, and double-deviant tones. Generalized linear mixed models tested the association between neighborhood social fragmentation and the frontal-central averaged MMN for three deviant types for youth at CHR-P and HC separately. The models adjusted for age, sex, race/ethnicity, parental education, parental history of psychosis, and neighborhood poverty. Participants (mean [SD] age: 18.69 [4.59], 41.9

BACKGROUND:Sensory prediction allows the brain to anticipate and parse incoming self-generated sensory information from externally generated signals. Sensory prediction breakdowns may contribute to perceptual and agency abnormalities in psychosis (hallucinations, delusions). The pons, a central node in a cortico-ponto-cerebellar-thalamo-cortical circuit, is thought to support sensory prediction. Examination of pons connectivity in schizophrenia and its role in sensory prediction abnormalities is lacking. METHODS:We examined these relationships using resting-state functional magnetic resonance imaging and the electroencephalography-based auditory N1 event-related potential in 143 participants with psychotic spectrum disorders (PSPs) (with schizophrenia, schizoaffective disorder, or bipolar disorder); 63 first-degree relatives of individuals with psychosis; 45 people at clinical high risk for psychosis; and 124 unaffected comparison participants. This unique sample allowed examination across the psychosis spectrum and illness trajectory. Seeding from the pons, we extracted average connectivity values from thalamic and cerebellar clusters showing differences between PSPs and unaffected comparison participants. We predicted N1 amplitude attenuation during a vocalization task from pons connectivity and group membership. We correlated participant-level connectivity in PSPs and people at clinical high risk for psychosis with hallucination and delusion severity. RESULTS:Compared to unaffected comparison participants, PSPs showed pons hypoconnectivity to 2 cerebellar clusters, and first-degree relatives of individuals with psychosis showed hypoconnectivity to 1 of these clusters. Pons-to-cerebellum connectivity was positively correlated with N1 attenuation; only PSPs with heightened pons-to-postcentral gyrus connectivity showed this pattern, suggesting a possible compensatory mechanism. Pons-to-cerebellum hypoconnectivity was correlated with greater hallucination severity specifically among PSPs with schizophrenia. CONCLUSIONS:Deficient pons-to-cerebellum connectivity linked sensory prediction network breakdowns with perceptual abnormalities in schizophrenia. Findings highlight shared features and clinical heterogeneity across the psychosis spectrum.

Mismatch negativity (MMN) event-related potential (ERP) component reduction, indexing N-methyl-D-aspartate receptor (NMDAR)-dependent auditory echoic memory and short-term plasticity, is a well-established biomarker of schizophrenia that is sensitive to psychosis risk among individuals at clinical high-risk (CHR-P). Based on the NMDAR-hypofunction model of schizophrenia, NMDAR-dependent plasticity is predicted to contribute to aberrant neurodevelopmental processes involved in the pathogenesis of schizophrenia during late adolescence or young adulthood, including gray matter loss. Moreover, stress and inflammation disrupt plasticity. Therefore, using data collected during the 8-center North American Prodrome Longitudinal Study (NAPLS-2), we explored relationships between MMN amplitudes and salivary cortisol, gray matter volumes, and inflammatory cytokines. Participants included 303 CHR-P individuals with baseline electroencephalography (EEG) data recorded during an MMN paradigm as well as structural magnetic resonance imaging (MRI) and salivary cortisol, of which a subsample (n = 57) also completed blood draws. More deficient MMN amplitudes were associated with greater salivary cortisol and pro-inflammatory cytokine levels in future CHR-Converters, but not among those who did not convert to psychosis within the next two years. More deficient MMN amplitude was also associated with smaller total gray matter volume across participants regardless of future clinical outcomes, and with subcortical gray matter volumes among future CHR-Converters only. These findings are consistent with the theory that deficient NMDAR-dependent plasticity results in an overabundance of weak synapses that are subject to over-pruning during psychosis onset, contributing to gray matter loss. Further, MMN plasticity mechanisms may interact with stress, cortisol, and neuroinflammatory processes, representing a proximal influence of psychosis.