| Objective:Temporal interference fields stimulation(TI)is a new technique that has been proposed in recent years to produce a distinct envelope-modulated electric field(the difference in frequency between the two high-frequency fields is within the oscillatory range of the brain,e.g.10,20,40 Hz,etc.)in the target brain region by means of two high-frequency(≥1 k Hz)electric fields.The electric field is used to modulate deep brain structures without recruiting neurons above the cerebral cortex.Current studies have confirmed the facilitatory effects of 20 Hz differential frequency TI stimulation in terms of motor cortex functional connectivity,motor control tasks and motor cortex excitability,but studies have not yet explored the possible effects of other differential frequency TI stimulation and their possible temporal effects.Therefore,the present study will compare the changes in primary motor cortical excitability before and after different differential frequency TI stimuli(10,20,40Hz,Sham)to test the hypothesis that different differential frequency TI stimuli have different modulatory effects on motor cortical excitability.Methods:A randomized,double-blind,crossover,controlled experimental design was used.26 healthy adults participated in this study.The subjects participated in a randomized order for a total of 4 sessions of TI stimulation at 10,20 and 40 Hz differential frequency and Sham stimulation,with an interval of at least 48 h.The TI stimulation protocol:electrodes were positioned C1,F1,C5 and F5,with C1 and F1as one current,C5 and F5 as one current;one current intensity was 2 m A peak-to-peak;one current frequency is 2000Hz,the other currents are 2010Hz,2020Hz and 2040Hz;the stimulation time is 20min and the fade in and fade out time is 30s.Motor evoked potentials(MEP)and resting motor thresholds(RMT)were measured using transcranial magnetic stimulation(TMS)in the target and contralateral(right primary motor cortex)areas before,immediately after,30min and 60min after each intervention.Two-Way Repeated Measures ANOVA was used to analyse the effects of the intervention modality and time factors on motor cortical excitability.Results:The experiment was well blinded,with subjects reporting weak side effects of TI stimulation and no reports of serious adverse effects.(1)20 Hz differential frequency TI stimulation:Statistical results showed a significant interaction between the two factors of intervention mode and time on motor evoked potentials in the stimulated target area(F(9,225)=2.166,p=0.025,η_p~2=0.080).Further analysis revealed that the amplitude of motor evoked potentials in the stimulated target area was significantly increased after the intervention compared to the Sham group(p=0.024),and the effect lasted up to 1 hour;for the contralateral side of the stimulation(right primary motor cortex),there was a tendency for motor evoked potentials to decrease immediately after the intervention;for resting motor thresholds,there was no significant stimulation effect in the primary motor cortex of both hemispheres(p>0.05).(2)10 Hz and 40 Hz differential frequency TI stimulation:there was no significant difference in the amplitude of motor evoked potentials and resting motor thresholds in the primary motor cortex of the two hemispheres before and after the intervention(p>0.05);For resting motor thresholds,after the 40 Hz differential frequency TI stimulation intervention,the stimulation target area showed a decreasing trend immediately after the intervention,while the contralateral side of the stimulation(right primary motor cortex)showed an increasing trend..Conclusion:The 20 Hz differential frequency TI stimulation increased the excitability of the motor cortex in the target area and the effect lasted up to 60 min.10Hz and 40Hz differential frequency TI stimulation did not significantly increase motor cortical excitability in the target area,but the 40 Hz differential frequency TI stimulation intervention showed an increasing trend.This study is a reference to further explore the effects of TI stimulation on human locomotor performance,with the aim of optimising the TI stimulation protocol and ultimately helping to enhance human locomotor performance. |
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