Acute Effects of Transcranial Direct Current Stimulation on the Gamma Auditory Steady-State Response in Healthy Controls

Schizophrenia is associated with disturbed auditory perceptions including auditory verbal hallucinations (AVH), which have been related to aberrant phase-locking of gamma-band steady state responses and have responded to treatment with transcranial direct current stimulation (tDCS). The objective of this study was to examine the effects of a single session of tDCS on auditory cortex responsiveness by assessing EEG power and phase measures of the 40-HZ auditory steady-state response (ASSR). In a randomized, crossover, sham-controlled design, 20 min of 2 mA anodal tDCS over the left prefrontal cortex in 30 healthy participants significantly increased 40-HZ ASSR spectral power and phase locking compared with sham tDCS. Increases in gamma power with anodal stimulation correlated with sham evoked gamma power, indicating a baseline-dependant relationship in which individuals with smaller baseline gamma power exhibit greater power increases with tDCS. This data suggests that altered gamma circuitry may be one mechanism underlying AVH responsiveness to tDCS in schizophrenia patients.