Secondary data analysis of auditory steady-state response to explore the RDoC cognitive system constructs across the psychosis spectrum

Hallucinations and cognitive impairments associated with psychosis may be underpinned by N-methyl D- aspartate (NMDA) receptor hypofunction. Within the Research Domain Criteria (RDoC) developed by the National Institute of Mental Health, features of psychosis illness, which can also be transiently produced in

healthy normal subjects given NMDA receptor antagonists, fall under the Cognitive System domain. Within this domain, auditory perception and processing speed are most relevant to the proposed work. Research focused on the abnormal functioning of this cognitive system in both psychosis and psychosis vulnerability

subject groups may increase understanding of these symptoms. Electroencephalography (EEG) has great potential to elucidate the potential link between NMDA receptor hypofunction and symptoms of illness. Gamma (30-80Hz) oscillations are known to be generated by fast- spiking interneuron and pyramidal neuron microcircuits, and NMDA receptors play an important role in fast-

spiking interneuron activity. Using spectral decomposition to analyze EEG, frequency-specific oscillations, including the gamma band, can be isolated and extracted on a millisecond basis. The auditory steady-state response (ASSR) is often used to study impaired EEG gamma oscillations in schizophrenia. These tasks use

short-duration trains of repetitive auditory stimulation at a fixed frequency (e.g., every 25ms or 40-Hz) to evoke an ASSR at that same frequency. In particular, the 40-Hz ASSR is typically reduced in evoked response power and exhibits more oscillation phase variability, or reduced phase synchrony, across trials in

schizophrenia. These deficits have also been observed in first-degree relatives and individuals at clinical-high risk (CHR) for psychosis. More recently, two additional measures derived from ASSR have demonstrated sensitivity to psychosis pathophysiology. These measures are (1) spontaneous gamma band power in the pre-

stimulus baseline period, which is abnormally elevated in schizophrenia, and (2) the 40-Hz ASSR oscillation phase angle, which is significantly delayed in schizophrenia. In a series of previously conducted studies across 9 laboratories, we collected 40-Hz ASSRs from chronically ill (i.e. > 5-years duration) psychosis patients, early illness (i.e.