| Objective: Temporal interference electrical fields(TI)stimulation is a novel brain modulation technique that has received much attention from researchers because of its non-invasive and deep-target properties.At present,there are few studies related to TI technique,and the comparison of the electric field and regulatory effects with transcranial alternating current stimulation(t ACS)is more helpful for in-depth understanding of the regulatory characteristics of TI stimulation.In this study,Temporal interference electrical stimulation system(TIESS)was developed based on previous studies,and TI was applied to healthy adults via the system.A frontoparietal in-phase TI stimulation protocol was proposed based on the neural basis of working memory.We set up a frontoparietal in-phase transcranial alternating current stimulation protocol for control to investigate the difference of simulated electric field between this two protocols and the effects on working memory performance.Methods: The current study was conducted with a randomized,parallel-controlled experimental design.A total of 60 healthy adults were recruited and randomly divided into four groups,including: TI group,t ACS group,TI sham group,and t ACS sham group.The output of the TIESS was verified by measuring the characteristics of the voltage and the stability of the current output by the system at different resistances(1-10 KΩ).The stimulation target of this study was the middle frontal gyrus and inferior parietal lobule,that is,F4 and P4 of the EEG 10/20 system.For each target region,TI stimulation consisted of two high frequency alternating current(2000 Hz and 2006 Hz),and the peak-to-peak amplitude of the current was 2 m A.Sinusoidal currents with a 6 Hz frequency value were used for t ACS and the peak-to-peak amplitude was 2 m A without DC offset.Electromagnetic computation was performed to calculated the electric fields of TI and t ACS protocols.Two sham stimulation only consisted of a ramping up stage and a fade-out stage.Both stages lasted 15 s.Each participant completed tasks consisting of 1,2,and 3 back verbal tasks before,during,and immediately after the stimulation session(pre-,during-,and after stimulation).Percent change values of reaction time,accuracy and inverse efficiency score(reaction time/accuracy)were quantified.One-way ANOVA was used to analyze the effects of different stimulation on the values.Results:(1)Temporal interference electric stimulation system can output stable current and voltage,which can meet the demand of the experiment.(2)Simulation results revealed that the frontoparietal in-phase TI stimulation protocol was able to produce hot spots in the target areas and produced a more focused stimulus compared to frontoparietal in-phase t ACS.The results also showed that,the maximum field amplitude in the hot spot of the isolated t ACS field was only half of the TI field when the peak-to-peak amplitude of each current was the same.(3)Behavioral results: An interaction effect between different groups was found in the 3-back condition for the percent change between after stimulation period and before stimulation period,and post-hoc analysis revealed a significant reduction in reaction time for the TI stimulation compared to the t ACS sham group.t ACS showed a significant increase for both reaction time and inverse efficiency scores compared to the t ACS sham stimulus group.An interaction effect was found in the 1-back condition for the percent change between during stimulation period and before stimulation period,and post-hoc analysis revealed a significant improvement of the subjects in the TI sham group.(4)The discomfort produced by the TI stimulation was only mild to moderate and did not differ compared to t ACS.Conclusion: The temporal interference electric stimulation system designed in this study can be stably used to apply TI stimulation,and the adverse events of TI stimulation are no different from those of traditional t ACS.The frontoparietal in-phase temporal interference stimulation in this study can generate more focal hotpots in target sites.The TI protocol is an effective technique to enhance working memory performance,but the regulatory effects did not better than the effects of t ACS. |
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