Differential modulation of the auditory steady state response and inhibitory gating by chloral hydrate anesthesia

Auditory steady state response (ASSR) and inhibitory gating (IG) are electrophysiological examinations commonly used to evaluate the sensory and cognitive functions of the brain. In some clinic examinations and animal experiments, general anesthesia is necessary to conduct electrophysiological recordings. However, the effects of anesthesia on ASSR and IG remain unclear. For this reason, we recorded local field potentials though electrodes implanted in different brain areas of rats: the auditory cortex (AC), hippocampus (HC), amygdala (AMY), and prefrontal cortex (PFC), and compared the characteristics of ASSR and IG under anesthetized and conscious conditions. We found that ASSR signals were the strongest in the AC, and decreased sequentially in the HP, AMY, and PFC. Chloral hydrate anesthesia significantly reduced the power and phase-locking of ASSR in the AC, HP, and AMY. In contrast, the extent of IG in the AC was weakest and it increased sequentially in the HP, AMY, and PFC. Anesthesia had less effect on the extent of IG. Our results suggest that ASSR and IG may originate from different neural circuits and that IG is more resistant to general anesthesia and therefore better suited to examining the functioning of non-auditory brain regions.