ABSTRACT
Gamma band neural oscillations in the human electroencephalogram (EEG) play an important role in perceptual and cognitive processes. Auditory steady state responses (ASSR) can probe neural oscillations with respect to phase synchronization and response magnitude. EEG recordings in bipolar disorder and schizophrenia patients showed reduced evoked power and phase locking for 40 Hz ASSR. Also, several studies have reported increased evoked power and decreased synchronization of the gamma band in patients with Alzheimer's disease. ASSR deficits in various psychiatric disorders may index disturbances of gamma-aminobutyric acid neurotransmission within auditory pathways and cortex. Although, several studies have reported ASSR deficits in various psychopathologies of psychiatric illness, further studies are necessary that investigate biological mechanism based on the ASSRs. In this review, the current concept and biological mechanism of ASSRs are discussed.