Gamma auditory steady-state response and remission in antipsychotic-naïve patients at clinical high risk for psychosis: a longitudinal study

OBJECTIVES: Patients at clinical high risk (CHR) for schizophrenia experience a wide range of clinical outcomes. Given this heterogeneity, long-term prognostic biomarkers are needed. The gamma-frequency EEG auditory steady-state response (ASSR) is deficient in schizophrenia, and a promising predictive biomarker of CHR outcomes. We hypothesised that reduced gamma ASSR would be associated with future symptom nonremission in CHR patients. METHODS: 36 help-seeking, antipsychotic-naïve CHR outpatients and 21 healthy control participants (HCPs) had EEGs recorded while they listened to 1-ms, 93-dB clicks presented at 40 Hz in 500-ms trains with 500-ms intertrain intervals. Mean 40-Hz evoked power (EP) and intertrial phase-locking factor (PLF) were measured from 0-500 ms post click-train onset. We compared EP and PLF between CHR patients who remitted over a two-year follow-up period, those who did not remit, and HCPs. RESULTS: CHR nonremitters, but not remitters, had larger EP than HCPs. CONCLUSIONS: The direction of the abnormality in gamma ASSR EP in CHR nonremitters (larger than in HCPs) was contrary to our hypothesis, and may represent a stage of cortical hyperexcitability in the pathophysiological trajectory to psychosis. Gamma ASSR may be a useful addition to prognostic algorithms for patients at CHR for psychosis.