Effects Of Brain Network-based Transcranial Direct Current Stimulation On Gait Characteristics In Healthy Adults

Purpose: Brain Network-based Transcranial Direct Current Stimulation(Network t DCS)is a new neurological intervention that uses t DCS to modulate the activity within and between single or multiple brain networks,using the resting brain network as the primary target.Compared to conventional t DCS,Network t DCS is able to target functional brain networks more precisely and to exert specific modulation effects.However,the effect of this technique on the modulation of gait behaviour has not been validated.Therefore,the aim of this study was to investigate the specific effects of Network t DCS on different gait characteristics in healthy adults: 1)the effects of a PFN+/DN-t DCS protocol that promotes excitability of the Frontoparietal network(PFN)and suppresses the Default network(DN)on gait speed under different walking conditions;2)the specific effects of Network t DCS on gait speed under different walking conditions;and 3)the specific effects of Network t DCS on gait speed under different walking conditions.(2)the specific effects of a DAN+/DN-t DCS scheme that promotes the excitability of the dorsal attention network(DAN)while suppressing the DN on gait variability under different walking conditions;further validate the causal relationship between brain network modulation of gait characteristics and provide a new brain-based network-based neuromodulation technique.Methods: This study used a randomised controlled trial design to investigate the specific effects of the FPN+/DN-t DCS protocol and the DAN+/DN-t DCS protocol on gait characteristics in two separate experiments(Experiment 1 and Experiment 2).Forty-eight healthy adults were recruited in each experiment and randomised to either the Network t DCS group or the sham stimulation group,with 24 individuals in each group.Of these,Experiment 1 used the FPN+/DN-t DCS protocol and Experiment 2used the DAN+/DN-t DCS protocol: 1)Experiment 1: each subject was required to receive either 1 session of FPN+/DN-t DCS(promoting FPN excitability while inhibiting DN excitability)or FPN+/DN-sham(sham stimulation);2)Experiment 2:each subject was required to receive 1 session of DAN+/DN-t DCS(promoting DAN excitability while inhibiting DN excitability)or DAN+/DN-sham(sham stimulation).The stimulation time for both experiments was 20 min,the total current intensity was less than 4 m A and the maximum current intensity at any electrode was less than 2m A.Sham stimulation provided only 1 min of current at the beginning of the stimulation,consisting of a 30 s slow rise and a 30 s slow fall.Subjects’ cognitive function(Experiment 1 assessed executive function,Experiment 2 assessed attentional function)and gait task performance(gait temporal parameters,gait variability,dual task cost,computational tasks,etc.)were assessed in Experiments 1-2both before and immediately after stimulation.A two-factor(stimulus protocol x preand post-stimulus)repeated measures ANOVA was used to analyse the effects of the above stimulus protocols on the subjects’ various parameters.Results: Experiments 1 and Experiments 2 were well blinded and did not report any serious adverse events,with subjects correctly inferring stimulus types of 48.00% and50.04%,respectively.1)Experiment 1: 40 subjects(20 in each group)completed all experimental tests and were included in the statistical analysis.The results revealed a significant increase in step width variability of 22.57%(p < 0.05)after FPN+/DN-sham(sham stimulation)and no significant change in gait variability in the FPN+/DN-t DCS group.In addition,FPN+/DN-t DCS significantly reduced the reaction time of the executive function under inconsistent conditions(p < 0.05),namely the executive function was significantly enhanced.2)Experiment 2: 48subjects(24 in each group)completed all experimental tests and were included in the statistical analysis.Results found that after DAN+/DN-t DCS there was a significant reduction in gait width variability of 21.2%(p < 0.05)reduction in gait width variability in fast gait and a significant 20.7%(p < 0.05)reduction in gait width variability in dual task gait.At the same time,DAN+/DN-t DCS significantly reduced the executive effect in the attentional network test(p < 0.05),namely a significant increase in attentional functioning.Conclusions: Brain network-based transcranial direct current stimulation is a new method to specifically modulate gait parameters.This study validates the important role of brain networks in gait neuromodulation and adds to the research evidence that non-invasive brain stimulation techniques improve gait function.In particular,DAN+/DN-t DCS protocols that target stimulation of the DAN and DN specifically reduce gait variability in healthy adults.There is a need to further optimise the stimulation protocols and to investigate the specific effects and underlying neurobiological mechanisms of these stimulation protocols on gait characteristics in people with slow gait speed and high gait variability.