Margaret Niznikiewicz1,2, Peter Bachman3, Aysenil Belger4, Ricardo Carrión5, Erica Duncan6, Jason Johannesen7, Brian J. Roach8, Jean Addington9, Kristin Cadenhead10, NAPLS Consortium, Daniel H. Mathalon8,11; 1VA Boston Healthcare System, 2Harvard Medical School, 3University of Pittsburgh, 4University of North Carolina, 5Zucker Hillside Hospital, 6Emory University, 7Yale University, 8San Francisco VA Healthcare System, 9University of Calgary, 10University of California, San Diego, 11Univeristy of California, San Francisco
Purpose: Abnormalities in gamma-band auditory steady-state response (ASSR) are an index of dysfunction in neural oscillations associated with GABAergic interneuron function and related to cognitive dysfunction in schizophrenia (SZ). A robust finding in SZ, they are regarded as one of its biomarkers. However, it is not clear if this abnormality is present already in individuals at clinical high risk for psychosis (CHR) and whether it distinguishes between those who will convert to schizophrenia and those who will not. As part of the NAPLS study we examined ASSR at both baseline and post-stimulus time-windows to address this important question. Materials and Methods. 439 CHR and 236 healthy controls (HC) were tested on the ASSR paradigm using 20, 30, and 40 Hz click-trains. Baseline power was examined within -200-0 msec window. The inter-trial phase coherence (ITC) was examined within 1. 0-200 msec post-stimulus latency window to interrogate early gamma-band response and 2. 200-500 msec post-stimulus window, to interrogate late gamma-band response. Results: For 40Hz click stimulation but not for 20 or 30 Hz, the baseline power was larger in CHR than in HC at both Fz (p=.04) and Cz (p=.04). In contrast, reduced ITC was observed for 40 Hz click-trains for latency windows of 200-300 msec (p=0.006), 300-400 msec (p=0.023) and 400-500 (p=0.34), (i.e., late gamma-band response). No measure distinguished between CHR-converters and non-converters. Conclusions: These results suggest that measures of baseline power and of ITC at 40 Hz distinguish between HC and CHR but are not sensitive to the conversion status.
