Study On The Effect Of High-definition Transcranial Direct Current Stimulation Combined With Slow-wave Sleep On Episodic Memory

Background: Sleep is a basic physiological process to maintain important human functions and physical and mental health.It plays a positive role in cognitive promotion and emotional regulation,especially slow wave sleep plays a key role in memory consolidation.Memory is one of the important components of cognitive function,which is easily affected by normal aging and different neuropsychiatric diseases,and impairs the daily life and cognitive function of individuals.Neuromodulation technology to enhance brain sleep processes to consolidate memory processing has attracted wide attention from brain science researchers.It have found that transcranial direct current stimulation(tDCS)has a regulatory effect on sleep-dependent memory consolidation,but the effect and neural mechanism are still unclear.Objective: The purpose of this study is to explore the effect of high-definition transcranial direct current stimulation(HD-tDCS)on episodic memory in healthy college students during the slow wave sleep of nap.Based on resting-state EEG to explore the power spectral density(PSD)change characteristics before and after transcranial direct current stimulation intervention during the slow-wave sleep of nap,and to try to parse the neural mechanism of HD-tDCS in promoting memory function.Method: Ninety-two healthy college students recruited from Anhui Medical University from December 2020 to December 2022 were selected to measure the general demographic characteristics and neuropsychological cognitive scale before enrollment.The groups were randomized into anodal HD-tDCS sleep group,sham-stimulated HD-tDCS sleep group,and anodal HD-tDCS awake group.The anodal HD-tDCS sleep group was given 0.5m A and 25 min stimulation during the slow wave sleep period of the midday nap,the sham-stimulated HD-tDCS sleep group was given sham stimulation during the slow wave sleep period of the midday nap,and the anodal HD-tDCS awake group was given 0.5m A and 25 min anodic stimulation when the subjects were awake during the waking period.The stimulation target of the three groups was the left dorsolateral prefrontal lobe.The participants in the anode HD-tDCS sleep group and the sham-stimulated HD-tDCS sleep group were all tested for episodic memory and EEG data collection before and after nap,while the anodal HD-tDCS awake group was collected for behavioral and EEG data at equal intervals during the waking period.Results: Comparison of general demographic characteristics of the three groups of participants: there was no significant difference in gender,age and years of education(all P>0.05),and there was no significant difference in neuropsychological cognitive assessment and Pittsburgh sleep quality index score among the three groups of participants(all P>0.05).In the associative memory test,there was a statistically significant difference in the degree of improvement among participants in the three groups before and after the intervention(P<0.05);and in the anodal HD-tDCS sleep group,the associative memory scores were significantly higher after the intervention compared with those before the intervention,which was statistically significant(P<0.05).In the Chinese’s version of the Auditory Verbal Learning Test(CAVLT),the immediate recall scores of participants in the anodic HD-tDCS sleep group and the sham-stimulated HD-tDCS sleep group were significantly improved before and after the intervention(P<0.05);In the anode HD-tDCS sleep group,the score of immediate recall after intervention was significantly higher than that before intervention(P<0.05);In the sham-stimulated HD-tDCS sleep group,the score of immediate recall after nap was higher than that before sleep(P<0.05).Power spectral density analysis revealed that the power spectral density in the theta band of the frontoparietal region was significantly reduced after stimulation in both the anodal HD-tDCS sleep group and the sham-stimulated HD-tDCS sleep group compared to the anodal HD-tDCS awake group.Correlation analysis suggested that the baseline values of theta-band PSD before stimulation in the anodal HD-tDCS sleep group and sham-stimulated HD-tDCS sleep group were significantly correlated with the difference in associative memory scores,that is,the greater the baseline PSD value of theta band,the more obvious the improvement of associative memory score.Conclusions: The results of this study indicate that anodic high-precision transcranial direct current stimulation acting on the left dorsolateral prefrontal cortex during slow wave sleep can significantly improve episodic memory function in healthy college students,and the altered power spectral density in theta frequency band may be an important neural mechanism.