Uncovering key predictive channels and clinical variables in the gamma band auditory steady-state response in early-stage psychosis: a longitudinal study.

Objective: Psychotic disorders are characterised by abnormalities in the synchronisation of neuronal responses. A 40 Hz gamma band deficit during auditory steady-state response (ASSR) measured by electroencephalogram (EEG) is a robust observation in psychosis and is associated with symptoms and functional deficits. However, the majority of ASSR studies focus on specific electrode sites, while whole scalp analysis using all channels, and the association with clinical symptoms, are rare.

Methods: In this study, we use whole-scalp 40 Hz ASSR EEG measurements – power and phase-locking factor – to establish deficits in early-stage psychosis (ESP) subjects, classify ESP status using an ensemble of machine learning techniques, identify correlates with principal components obtained from clinical/demographic/functioning variables, and correlate functional outcome after a short-term follow-up.

Results: We identified significant spatially-distributed group level differences for power and phase locking. The performance of different machine learning techniques and interpretation of the extracted feature importance indicate that phase locking has a more predictive and parsimonious pattern than power. Phase locking is also associated with principal components composed of measures of cognitive processes. Short-term functional outcome is associated with baseline 40 Hz ASSR signals from the FCz and other channels in both phase locking and power.

Conclusion: This whole-scalp EEG study provides additional evidence to link deficits in 40 Hz ASSRs with cognition and functioning in ESP, and corroborates with prior studies of phase locking from a subset of EEG channels. Confirming 40 Hz ASSR deficits serves as a candidate phenotype to identify circuit dysfunctions and a biomarker for clinical outcomes in psychosis.