| Purpose:Ankle force sense is critical to human postural control,but the traditional improvement strategies for ankle force sense,such as balance training and strength training,require a longer period and have inconsistent effects.One possible reason is that previous studies have not fully utilized the central nervous system in the regulation of ankle force sense.In recent years,high-definition transcranial direct current stimulation（HD-t DCS）has attracted much attention in the field of improving human ability,which is believed to be able to modulate the central nervous system more accurately to improve human sensorimotor function.However,the effect of HD-t DCS on ankle force sense is still unknown,and the underlying mechanisms of its influence on lower limb sensorimotor function are also inconsistent.Therefore,the aim of this study was to explore the immediate effects of HD-t DCS on ankle muscle sensation in healthy adults,and to explore the potential mechanism by monitoring the hemodynamics response of the relevant cortex.Methods:Sixteen healthy adults（8 males and 8 females;age:25.5±1.8 yrs;height:170.8±10.9 cm;weight:63.9±11.9 kg）were recruited for this experiment using a randomized,double-blind,crossover design.Each subject completed 2 experiments which separated by 3 to 7 days.In each experiment,subjects first performed a force sense test of the right ankle plantarflexion muscles,which consisted of three active plantarflexion force reproduce without feedback after three 25%MVIC force control learning sessions based on the force feedback curve.After completion of the pre-test,subjects received HD-t DCS intervention（20 min,2 m A,real or sham stimulation in a randomly assigned order）targeting the primary motor cortex（M1）,followed by a post-test of the right ankle force sense.During the ankle force sense test,functional near-infrared spectroscopy（f NIRS）was used to monitor changes in the hemodynamics of sensorimotor cortex.Major areas covered by f NIRS channels including primary somatosensory cortex,primary motor cortex,premotor and supplementary motor cortex,and somatosensory association cortex.A two-way ANOVA with repeated measures was used to examine the effects of stimulation condition and time on the performance of ankle force sense test,sensorimotor cortical activation,and sensorimotor cortical functional connectivity.A correlation analysis was used to examine the relationship between the change in the performance of ankle force sense test and the change in cortical activation and functional connectivity after the intervention,respectively.Results:1)The two-way ANOVA with repeated measures revealed a significant main effect of time for root mean square error of the ankle force sense test(F[1,30]=9.899,p=0.004,=0.248),specifically a 19.97%decrease in the real HD-t DCS condition and a 10.23%decrease in the sham condition after the intervention;2)there was a significant interaction between time and stimulation condition for sensorimotor cortex activation during ankle force sense test(F[1,30]=9.899,p=0.004,=0.248),with post-hoc tests showing that activation of channel 2 was significantly higher after real HD-t DCS（p=0.02,Cohen’s d=0.91）,whereas activation of this channel was not significantly different after sham stimulation;3)there was a significant main effect of time for functional connectivity between channel 2 and channel 4(F[1,30]=8.066,p=0.008,=0.212),specifically a 53.88%decrease after real HD-t DCS and a 13.01%decrease after sham stimulation;4)the linear regression analysis showed that in the real HD-t DCS condition,the decrease in functional connectivity between channel 2 and channel 4 was significantly correlated with the decrease in root mean square error of ankle force sense（Pearson’s r=0.544,p=0.029）.Conclusions:HD-t DCS enhanced the cortical activation of supplementary motor area during ankle force sense tests in healthy young adults,and in the real HD-t DCS condition,the decrease in interhemispheric functional connectivity in supplementary motor area was significantly associated with improved ankle force sense.It is suggested that HD-t DCS used in this study can elevate cerebral cortex excitability and modulate the interhemispheric functional connectivity,and can be used as a potential intervention to enhance ankle force sense.This study provides a theoretical basis for improving ankle muscle force sensation at the level of central nervous system and offers new ideas for promoting the effectiveness and precision of ankle force sense intervention strategies. |
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