Gamma auditory steady-state response as a promising electrophysiological biomarker for depression: an in vivo study with chronic unpredictable mild stress (CUS)-induced rats.

Gamma oscillations play a functional role in brain cognitions. Recently, auditory steady-state response (ASSR) has been reported abnormally in depression clinically, particularly in the low-gamma band. However, clinical electroencephalography research has challenges obtaining pure signals straight from the source level, making information isolation and precise localization difficult. Besides, the ASSR deficits pattern remains unclear. Herein, we focused on the origin of ASSR-primary auditory cortex (A1), the central node in the auditory pathway. We assessed the evoked-power and phase-synchronization using local field potentials (LFP) in depression (n = 21) and control (n = 22) rats. Subsequent processing of the received auditory information was examined using event-related potentials (AEPs). Results showed that depressed rats exhibited significant gamma ASSR impairments in peak-to-peak amplitude, inter-trial phase coherence, and signal-to-noise ratio. These deficits were more pronounced during 40-Hz auditory stimuli in right-A1, indicating severe gamma network abnormalities in the right auditory pathway. Besides, increased N2 and P3 amplitudes in depression group were found, indicating excessive inhibitory control and contextual processing. Taken together, these ASSR abnormalities have a high specificity of more than 90% and high sensitivity of more than 80% to distinguish depression under 40-Hz auditory stimuli. Our findings provided an abnormal gamma network in the auditory pathway, as a promising diagnostic biomarker in the future.