Effects Of TACS Of Different Frequencies On Auditory Steady-state Response And Its Short-term Aftereffect

Transcranial Alternating Current Stimulation(t ACS)is a non-invasive brain stimulation method that can be used to regulate cognitive and memory functions.Due to the unique frequency-specific t ACS,it is suitable for regulating physiologically related brain oscillations in a specific frequency manner,and is expected to directly regulate rhythmic activities in the range of typical electroencephalography(EEG).In addition,Oscillatory activity in the brain is an important mechanism of the brain’s integrated functions,and the EEG activity in the gamma range(30-80 Hz)is related to the processing of sensory information and cognitive processes.Auditory steady-state responses(ASSR)recorded with EEG is a typical auditory evoked potential with high frequency specificity.The activity of ASSR reflects periodic activities related to the rhythm of the cerebral cortex.In order to explore the effect of t ACS on the excitability of the auditory cortex,In this study,different frequencies of t ACS combined with auditory stimulation were used to induce ASSR,and then revealed the excitatory/inhibitory effects of t ACS on the γ activity of the auditory cortex,and provided an electrophysiological basis for the interaction between t ACS and auditory cortex excitability.The study first explored the effect of α-t ACS(11 Hz)on the γ activity of the auditory cortex.The t ACS electrodes were placed in the temporal lobe of the auditory cortex,and the EEG data were recorded before stimulation,after pseudo stimulation,and after real stimulation.The results show that α-t ACS had an inhibitory effect on 40Hz-ASSR and reduced the endogenous oscillation activity in the low-frequency gamma band(30-38 Hz).At the same time,11 Hz-t ACS may enhanced the activity of the middle temporal gyrus regardless of the real/sham of the stimulation,and only the real stimulation of t ACS may reduce the activity of the posterior cingulate gyrus.This study preliminarily confirmed that α-t ACS in the auditory cortex has an inhibitory effect on ASSR.In order to further explore the regulation of frequency-specific t ACS on the excitability level of the auditory cortex.We adopted a random repeated measurement research design to evaluate the effects of α-t ACS(10 Hz)and γ-t ACS(40 Hz)on auditory steady-state activity.On the premise of one week interval,recorded the EEG data before and after the real/sham of t ACS stimulation.The results show that,compared with γ-t ACS and pseudo-stimulation,α-t ACS had a significant inhibitory effect on 40 Hz-ASSR.This result further reveals the direct modulation of brain oscillations by t ACS at a specific frequency.In addition,studies have shown that t ACS can induce a sustained after-effect for up to 30 minutes.The reason for this electrophysiology is still unclear,it may be consistent with synaptic changes,or it may be due to persistent hyperpolarization of membrane potential.In order to explore the sustained after-effect of auditory cortex t ACS on auditory steady-state activity,the study collected and analyzed the EEG data after α-t ACS and γ-t ACS stimulation 30 minutes.It was found that the inhibitory effect of α-t ACS can last for 30 minutes.The result further confirmed that t ACS can regulate the rhythmic activity of the brain at a specific frequency.