Effects Of Fronto-parietal θ Transcranial Alternating Current Stimulation On A Dual Task Of Working Memory-postural Control

Objective:Dual-task（i.e.walking or standing while performing a cognitive task）may interfere with the performance of one or both tasks.Based on capacity sharing theory,improving dual-task abilities such as postural control by improving cognitive functions（i.e.working memory）may be a feasible measure.In recent years,transcranial alternating current stimulation（tACS）has been found to have a greater potential to improve working memory performance,especially theta band stimulation in frontal-parietal regions.Therefore,the aim of this study was to investigate the effects of frontal-parietal tACS atθband on working memory-postural control dual-tasks performance.Methods:A within-subjects cross-over pilot study evaluated the effects of 20 mins of 6hz-tACS targeting both the left dorsolateral prefrontal cortex（LDLPFC）and posterior parietal cortex（PPC）in 20 healthy adults（21.6±1.3 years old）.During each session,closed-eye resting-state EEG acquisition and single-and dual-task behavioral tests（working memory single-task,static tandem standing,and a dual-task of working memory-postural control）were assessed before and immediately after stimulation.To determine the interference effects of the dual-task condition,differences in cognitive and postural control performance were analyzed using paired t-tests.Behavioral outcomes andθpower of RS-EEG were statistically analyzed using a 2×2（time×group）repeated measures ANOVA to examine the effect of tACS on working memory and upright standing performance as well as the RS-EEG;within-group analysis using paired t-tests.Pearson’s correlation analysis was used to investigate the correlation between the change of RS-EEG（Δ）and the change of behavioral outcomes（Δ）after different stimulus conditions（post-pre）.Results:1)When exploring the dual-task interference,all the sway velocity were significantly decrease under dual-task condition(V_ML:p=0.045,V_AP:p=0.004,and Vcop:p=0.011),we did not find any significant difference in working memory performance either on upright posture situations or seating conditions（ps>0.05）.2)No interaction between the two stimulation situations and the time factor across outcomes was found in the repeated measures ANOVA,but within-group analyses revealed a significant 5.3%decrease in working memory response time under the dual-task following the tACS（t=-3.157,p=0.005）;however,no differences were observed on either upright postural control performance or RS-EEG results（ps<0.05）.3)Correlation analyses revealed a significant correlation between increased RS-EEGθpower at the F3 and P3 channels and faster reaction time（r=-0.515,p=0.02;r=-0.483,p=0.031,respectively）in the working memory task after tACS.However,no differences were observed on either upright postural control performance or RS-EEG results（ps<0.05）.Conclusion:Fronto-parietalθ-tACS has potential as a neuromodulatory tool for improving working memory performance in dual-task situations,but its effect on the modulation of concurrently performed postural control tasks requires further investigation.