经颅直流电刺激干预工作记忆的脑功能网络研究

工作记忆是高级认知功能的重要基础,为探索经颅直流电刺激(tDCS)对工作记忆的影响及具体机制,招募18位被试参加实验,采集被试在伪/阳极/阴极tDCS刺激后三图、四图以及五图记忆负载任务中的行为数据(准确率、反应时长)与脑电信号。首先根据行为数据对工作记忆能力进行评估,再利用不同通道之间脑电信号的相关性,构建各状态下的脑功能网络,计算出平均度D、平均聚类系数C和全局效率E等网络特征参数,最后结合不同极性tDCS刺激后3种记忆负载任务中的行为数据与网络特征参数变化进行分析。研究表明,阳极刺激后四图与五图负载任务中的准确率(四图: 89.75%±1.36%;五图: 78.50%±2.25%)较伪刺激后(四图:81.25%±2.30%;五图: 73.25%±5.36%)均有显著提升(P<0.05),而阴极刺激后行为数据的变化无规律可循。根据脑功能网络特征参数的变化可以发现,阳极刺激后高度值节点主要分布在刺激点F3以及周围区域,3种记忆负载任务中的网络特征参数与伪刺激后相比均显著增加(P<0.05),且在四图负载任务中增幅最大(伪刺激:D=10.55±2.31,C=0.60±0.07,E=0.26±0.03;阳极刺激:D=15.37±1.35,C=0.71±0.04,E=0.34±0.02),而阴极刺激后的高度值节点主要分布在右侧额叶与枕叶区域,且网络特征参数只在五图负载任务中表现出显著降低(伪刺激:D=13.73±2.42,C=0.64±0.07,E=0.31±0.04;阴极刺激:D=11.46±2.31,C=0.58±0.05,E=0.28±0.03)。结果表明,阳极刺激通过激活左背外侧前额叶皮层活性,可有效提升工作记忆性能,且在难度适中的任务中提升效果更显著;阴极刺激可抑制该皮层活性,使大脑连通性能下降,但大脑选择其他脑区进行功能代偿,有较大的个体差异性,且抑制效果在高难度任务下更显著。     

不同视觉辅助刺激下运动想象大脑皮层因果连接网络特性分析

基于运动想象(MI)的脑-机接口系统(BCI)被认为是一种很有潜力的运动功能康复方法,但是经典MI-BCI使用时存在个体差异性大、识别率较低的问题。采用视觉辅助刺激范式可以增强MI特征,并能有效提高BCI识别的准确率。然而在不同的视觉辅助刺激范式下,MI任务期的大脑皮层因果连接响应特征及其面向运动功能康复的神经生理学意义却鲜有报道。设计4种不同类型的视觉辅助刺激范式,包括不同的动态/非动态视觉刺激及简单/复杂想象任务范式,选取MI任务期大脑运动感觉相关皮层7个感兴趣区域,利用孤立有效相干法(iCoh),对11名被试beta频段4种实验范式构建单尾单样本t检验(P<0.01)平均因果脑网络,并分析网络的平均度分布、聚类系数、全局效率、中介中心度参数。结果表明,相比于简单想象任务非动态视觉刺激范式,复杂想象任务动态视觉刺激范式平均度分布由2.143提高为2.429,聚类系数由0.634提高为0.767,全局效率由0.393提高为0.417。复杂想象任务动态刺激范式下,辅助运动皮层和顶上小叶、顶下小叶存在因果连接关系,辅助运动皮层成为脑网络中的关键节点。     

高特质焦虑个体执行控制功能及其脑网络研究

利用行为学及复杂网络分析方法,探讨高特质焦虑(HTA)个体执行控制功能及其脑功能网络特点。以16名HTA个体为研究对象、16名低特质焦虑(LTA)个体为对照,进行Simon空间认知冲突任务,同步记录行为数据(反应时间及正确率)及 64导脑电(EEG)信号。对EEG数据进行同步似然分析,选择合适阈值构建脑网络拓扑结构并计算网络整体属性参数及节点属性参数。利用方差分析方法,对两组被试的行为数据及脑网络属性参数进行统计学分析,结果显示, HTA组被试的冲突反应时间显著长于LTA组(641.29±72.11 vs 602.10±61.47, P< 0.05)、反应正确率显著低于LTA组(90.73±2.14 vs 95.62±1.52, P< 0.05),表明其认知冲突反应的效率降低、执行控制功能下降。对beta节律脑网络的分析显示:HTA组被试其额顶叶各节点的节点度值均显著小于LTA组(P< 0.05),聚类系数(0.5341±0.0813 vs 0.6243±0.0527)及全局效率(0.0142±0.0037 vs 0.0185±0.0023)均显著小于LTA组(P< 0.05),而特征路径长度显著大于LTA组(1.8057±0.0036 vs 1.4380±0.0117, P< 0.05);高gamma节律脑网络的各属性参数结果与beta节律相似。以上结果表明HTA个体冲突监控、冲突解决等执行控制能力下降, 其机制不仅与额顶执行控制网络功能受损有关,也与脑网络的整合功能及信息传输能力减弱有关。额顶执行控制网络功能受损、执行控制能力下降可能是HTA个体稳定、固有的特征。     

低频重复经颅磁刺激刺激初级运动皮层对大脑功能连接影响的研究

重复经颅磁刺激(rTMS)能对刺激脑区及与其相连接的远端脑区产生影响。本文将从大脑功能连接、脑区之间相互协调工作状态改变的角度,研究低频rTMS刺激脑初级运动皮层对大脑的影响作用。募集了10名健康受试者,采用1 Hz rTMS刺激脑初级运动皮层20 min,采集刺激前后1 min闭目静息状态下的脑电(EEG)数据。对EEG进行相位同步分析,建立脑功能网络,并计算脑功能网络特征参数。最后使用符号秩和检验进行统计学分析。结果表明,低频rTMS刺激使大脑alpha频段全局相位同步指数显著降低(P0.05)。两两脑区分析表现为刺激侧的运动皮层与额叶皮层和顶叶皮层、非刺激侧顶叶皮层与双侧额叶皮层之间alpha频段相位同步显著降低。alpha频段脑功能网络的平均度、全局效率降低(P0.05),平均最短路径长度显著增加(P0.05)。表明低频rTMS使脑功能网络的信息传输变慢,传输效率变低。本文从大脑功能连接性的角度上证明了低频rTMS对大脑活动的抑制作用,说明低频rTMS能够对刺激脑区及与刺激脑区相连接的远端脑区产生影响。本研究有望为低频rTMS应用于临床疾病的治疗提供一定的指导。     

阳极经颅直流电刺激对脑卒中患者脑功能网络的影响

经颅直流电刺激(tDCS)在脑卒中治疗中应用潜力巨大,但其作用效应仍不明确。本研究基于脑电图(EEG)和图论分析探讨阳极tDCS干预对脑卒中患者的作用效应。对15例脑卒中患者施加阳极tDCS真刺激和伪刺激,以随机顺序间隔一周进行两次刺激,每次采集刺激前和刺激后静息态EEG信号。对每次采集的EEG信号,采用皮尔逊相关系数等分析方法研究各个导联间的关联性特征参数。基于分析结果,构建患者刺激前、后的脑功能网络,并分析网络特征参数的变化。结果显示,真刺激后脑功能网络的平均度、平均聚类系数、全局效率以及“小世界”属性值较刺激前均显著增大(P<0.05),特征路径长度显著减小(P<0.05),而伪刺激组相关参数变化未见显著差异(P>0.05)。结果表明,阳极tDCS干预对卒中后恢复性治疗具有积极影响,为其临床应用提供了实验依据。     

磁刺激光明穴的脑电响应的脑功能网络构建与分析

经颅磁刺激技术与中医穴位刺激相结合的研究和应用,近年来已经取得一定进展,图论理论在脑科学研究领域中也进行一些探索,这些理论和技术的交叉与结合将为神经磁刺激技术的应用和脑科学的研究开启新的方向。利用互相关方法对磁刺激光明穴和假穴的脑电信号进行了两两通道间的线性时域关联特性分析,得出各通道间脑电数据的相关数量关系,并且以相关矩阵的形式表示,通过阈值大小的设定获取邻接矩阵,分别构建磁刺激光明穴与磁刺激假穴实验状态下脑电信号的脑功能网络图。结果发现,磁刺激光明穴的脑功能连接相比于磁刺激假穴的脑功能连接在枕叶(视觉联络区)、额叶区显著增多。利用基于图论的复杂网络理论,对所构建的脑功能网络特性参数进行参数比较和统计学分析。磁刺激光明穴使得脑功能网络发生变化,主要包括网络平均度增大、聚类系数增大、特征路径长度减小、全局效率和局部效率提高、小世界属性增强,并且这些差异经过统计学检验在均值差值上都有量化体现,通过统计检验发现磁刺激光明穴引起的脑功能网络参数的改变具有显著性差异(P<0.05)。研究提示,磁刺激光明穴相比磁刺激假穴,可以提高脑功能网络的全局效率和局部效率,缩短信息传播路径,使各个脑区之间的信息传递更加高效,为磁刺激技术施加于穴位改善神经功能提供一定的理论依据。     

基于偶极子特征优化的情绪重评同步EEG-fMRI源定位研究

为研究情绪重评时的大脑皮层源活动,针对情绪重评实验范式下采集的15例健康人同步EEG-fMRI数据,首先提出一种新颖的基于偶极子特征优化的融合源定位方法:根据fMRI加权最小范数估计源定位结果,采用20 ms EEG滑动时间窗,提取每个时窗内的偶极子空间融合特征,将其作为动态融合先验进行加权最小范数估计溯源;随后将该结果与fMRI加权最小范数估计源定位结果进行情绪重评机制上的对比;最后采用样本熵进行脑电源复杂度分析。实验结果表明,该方法可以在高时间和空间分辨率下,有效地追踪情绪重评任务下大脑皮层上的脑电源动态并识别出相关脑区。情绪重评过程中,随着后枕顶叶晚期正电位的出现,显著活跃脑区从左顶叶下部、右侧额中回下部、左侧脑岛转移到右侧颞上回和左外侧枕叶,最后在晚期正电位慢波阶段激活了右侧梭状回、右侧额中回下部和右侧扣带回峡部(P<0.05)。通过脑电源样本熵的计算,提取出被试在接受不同情绪刺激后1500 ms内的显著脑区(P<0.05):情绪响应的活跃脑区为左外侧枕叶(负性:0.688±0.124,中性:0.590±0.126);情绪重评的活跃脑区为右侧额中回下部(负性重评:0.814±0.114,负性:0.736±0.123);情绪重评的抑制脑区为右侧颞上回(负性:0.642±0.152,负性重评:0.546±0.090)。这些结果为情绪重评相关的皮层脑电源定位研究提供了脑区参考。     

鼻腔内机械振荡刺激对健康人群静息态脑电图相对功率及有效连接的影响

鼻腔内机械振荡刺激(iMVS)是一种新型的无创神经刺激技术, 可提升边缘系统内在功能活性从而改善自主神经平衡。通过分析iMVS对健康人群脑电图(EEG)相对功率以及EEG有效连接的影响,探索iMVS的神经生理机制。将22名健康成年被试随机均分为刺激组与对照组,并对11名刺激组被试两侧鼻腔各进行10 min的iMVS,11名对照组被试进行假刺激。在iMVS前和iMVS结束30 min后记录被试的静息态脑电图。采用Welch变换进行相对功率分析;采用直接定向传递函数(dDTF)进行有效连接分析;采用独立样本t检验、配对t检验以及FDR方法进行统计学分析。结果显示,iMVS后刺激组被试的alpha、beta频段EEG相对功率显著提升。刺激组alpha频段相对功率从51.57%±5.93%上升至57.33%±4.59%,其中C3、C4、T8、O1、O2导联的alpha频段相对功率提升显著(P<0.05);刺激组beta频段相对功率从7.28%±0.11%上升至8.36%±0.44%,其中C3、C4、T7、T8、O2导联的beta频段相对功率提升显著(P<0.05); iMVS后刺激组被试的alpha频段dDTF值显著提升,刺激组alpha频段dDTF值由0.052±0.0017提升至0.0592±0.0028,其中F4至F3、O2至F3、C4至F4、O2至F4、F3至C3、C4至C3、F3至T7、C4至T8、O2至O1方向的dDTF值显著提升(P<0.05)。刺激前后对照组的EEG相对功率以及EEG有效连接未见显著变化。大脑边缘系统的内在功能活性与alpha、beta频段EEG相对功率以及alpha频段EEG有效连接呈正相关。研究结果表明,在刺激结束30 min后iMVS技术对于边缘系统的内在功能活性具有提升作用。研究首次从脑电分析角度阐释iMVS改善自主神经平衡的相关机制,并为采用EEG相对功率和EEG有效连接作为iMVS效用评价的生物标记物提供证据。     

基于静息态fMRI相位同步的ADHD儿童脑网络研究

探索相位同步和复杂网络方法在注意缺陷多动障碍(ADHD)脑网络机制研究中的应用, 选取135例ADHD患者和102例正常对照作为研究对象。以这237例被试的功能磁共振图像时间序列作为研究数据, 利用相位同步分析方法获得脑区间的连接关系, 并在此基础上构建脑网络。然后, 利用复杂网络的局部效率指标评估静息态脑功能, 并采用多元线性回归和方差分析等统计方法, 分析ADHD患者和正常对照在静息态下脑区的局部效率可能存在的差异。结果表明, ADHD患者与正常对照在年龄、性别、量表分值(注意力和自制力)、3种智商值(语言智商、操作智商和总智商)等方面均无统计学差异, 在诊断和头动参数上有显著差异(P<0.05, 校正后)。诊断方面发现, 11个局部效率正常对照组与ADHD组具有统计学差异的脑区(P<0.05), 其中主要的脑区为左侧尾状核(0.118±0.317 vs 278±0.433)、丘脑(0.345±0.425 vs 0.541±0.435)、颞横回(0.467±0.476 vs 0.654±0.444)和右侧背外侧额上回(0.536±0.401 vs 0.681±0.333)、额中回(0.505±0.377vs 0.641±0.331)、尾状核(0.144±0.329 vs 0.298±0.423)。在静息态下, ADHD患者和正常对照在左侧中央前回、尾状核、丘脑等脑区的局部效率差异可能与患者尾状核、丘脑等特定脑区的功能异常有关, 也可能与患者注意和执行有关的神经网络损伤有关。     

老年人轻度认知障碍部分定向相干脑网络分析

近年的研究表明,轻度认知障碍(MCI)患者的认知加工呈现脑连通性缺失特征,但各脑区间如何影响,因果特性不明。本研究的目的在于分析MCI患者在认知任务下的有向脑网络特征。采集了30位老人在信息冲突颜色认知作业下的头皮脑电,包括21位正常人和9位MCI患者。选取刺激呈现后的脑电计算其部分定向相干值,依此构建脑网络,并着重分析了不同脑区的入度差异。研究发现：在beta段,MCI患者右前额区信息流入缺失,左中央区的信息流入异常增强;在患者组和正常组中前脑区的入度要远高于后脑区;正常人在匹配和不匹配刺激下右脑区的入度要高于左脑区;但是在患者组中左右脑区的入度却没有明显差别。在特定阈值下：正常人在匹配刺激下左脑区（阈值0.14）的入度要低于MCI患者（F=3.780,P=0.040）;正常人在不匹配刺激下左脑区（阈值0.26）的入度要低于MCI患者（F=3.780,P=0.040）;正常人在匹配刺激下右脑区（阈值0.18）的入度要高于MCI患者（F=3.941,P=0.021）。文章从入度为脑网络特征验证了MCI患者在颜色认知任务下右脑的功能缺损。     

Enhancement of pinch force in the lower leg by anodal transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is a procedure to polarize human brain. It has been reported that tDCS over the hand motor cortex transiently improves the performance of hand motor tasks. Here, we investigated whether tDCS could also improve leg motor functions. Ten healthy subjects performed pinch force (PF) and reaction time (RT) tasks using the left leg before, during and after anodal, cathodal or sham tDCS over the leg motor cortex. The anodal tDCS transiently enhanced the maximal leg PF but not RT during its application. Neither cathodal nor sham stimulation changed the performance. None of the interventions affected hand PF or RT, showing the spatial specificity of the effect of tDCS. These results indicate that motor performance of not only the hands but also the legs can be enhanced by anodal tDCS. tDCS may be applicable to the neuro-rehabilitation of patients with leg motor disability.     

Modulation of event-related desynchronization during motor imagery with transcranial direct current stimulation (tDCS) in patients with chronic hemiparetic stroke

Electroencephalogram-based brain–computer interface (BCI) has been developed as a new neurorehabilitative tool for patients with severe hemiparesis. However, its application has been limited because of difficulty detecting stable brain signals from the affected hemisphere. It has been reported that transcranial direct current stimulation (tDCS) can modulate event-related desynchronization (ERD) in healthy persons. The objective of this study was to test the hypothesis that anodal tDCS could modulate ERD in patients with severe hemiparetic stroke. The participants were six patients with chronic hemiparetic stroke (mean age, 56.8 ± 9.5 years; mean time from the onset, 70.0 ± 19.6 months; Fugl-Meyer Assessment upper extremity motor score, 30.8 ± 16.5). We applied anodal tDCS (10 min, 1 mA) and sham stimulation over the affected primary motor cortex in a random order. ERD of the mu rhythm (mu ERD) with motor imagery of extension of the affected finger was assessed before and after anodal tDCS and sham stimulation. Mu ERD of the affected hemisphere increased significantly after anodal tDCS, whereas it did not change after sham stimulation. Our results show that anodal tDCS can increase mu ERD in patients with hemiparetic stroke, indicating that anodal tDCS could be used as a conditioning tool for BCI in stroke patients.     

Enhancement of non-dominant hand motor function by anodal transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is a non-invasive powerful method to modulate brain activity. It can enhance motor learning and working memory in healthy subjects. To investigate the effects of anodal tDCS (1 mA, 20 min) of the dominant and non-dominant primary motor cortex (M1) on hand motor performance in healthy right-handed volunteers, healthy subjects underwent one session of both sham and active anodal stimulation of the non-dominant or dominant primary motor cortex. A blinded rater assessed motor function using the Jebsen Taylor Hand Function Test. For the non-dominant hand, active tDCS was able to improve motor function significantly-there was a significant interaction between time and condition of stimulation (p = 0.003). Post hoc tests showed a significant enhancement of JTT performance after 1 mA anodal tDCS of M1 (mean improvement of 9.41%, p = 0.0004), but not after sham tDCS (mean improvement of 1.3%, p = 0.84). For the dominant hand, however, neither active nor sham tDCS resulted in a significant change in motor performance. Our findings show that anodal tDCS of the non-dominant primary motor cortex results in motor function enhancement and thus confirm and extend the notion that tDCS can change behavior. We speculate that the under-use of the non-dominant hand with its associated consequences in cortical plasticity might be one of the reasons to explain motor performance enhancement in the non-dominant hand only.     

The enhanced cortical activation induced by transcranial direct current stimulation during hand movements

The aim of this study is to evaluate whether tDCS applied on the primary motor cortex (M1) in company with hand movements could enhance cortical activation, using functional MRI (fMRI). Twelve right-handed normal subjects were recruited. Real tDCS and sham tDCS with hand movements were applied during fMRI scanning. Subjects performed grasp-release hand movements at a metronome-guided frequency of 1Hz, while direct current with 1.0mA was delivered to the primary motor cortex. The averaged cortical map and the intensity index were compared between real tDCS with hand movements and sham tDCS with hand movements. Our result showed that cortical activation on the primary sensorimotor cortex was observed under both of two conditions; real tDCS with hand movements and sham tDCS with hand movements. Voxel count and peak intensity were 365.10±227.23 and 5.66±1.97, respectively, in the left primary sensorimotor cortex during real tDCS with right hand movements; in contrast, those were 182.20±117.88 and 4.12±0.88, respectively, during sham tDCS with right hand movements. Significant differences in voxel count and peak intensity were observed between real tDCS and sham tDCS (p<0.05). We found that anodal tDCS application during motor task enhanced cortical activation on the underlying targeted motor cortex, compared with the same motor task without tDCS. Therefore, it seemed that tDCS induced more cortical activity and modulated brain function when concurrently applied with motor task.     

Transcranial Direct Current Stimulation Modulates Neuronal Networks in Attention Deficit Hyperactivity Disorder

Anodal transcranial direct current stimulation (tDCS) of the prefrontal cortex has been repeatedly shown to improve working memory (WM). Since patients with attention deficit hyperactivity disorder (ADHD) are characterized by both underactivation of the prefrontal cortex and deficits in WM, the modulation of prefrontal activity with tDCS in ADHD patients may increase their WM performance as well as improve the activation and connectivity of the WM network. In the present study, this hypothesis was tested using a double-blind sham-controlled experimental design. After randomization, sixteen adolescents with ADHD underwent either anodal tDCS over the left dorsolateral prefrontal cortex (DLPFC, 1 mA, 20 min) or sham stimulation with simultaneous fMRI during n-back WM task. Both in one-back and two-back conditions, tDCS led to a greater activation (compared with sham stimulation) of the left DLPFC (under the electrode), left premotor cortex, left supplementary motor cortex, and precuneus. The effects of tDCS were long-lasting and influenced resting state functional connectivity even 20 min after the stimulation, with patterns of strengthened DLPFC connectivity after tDCS outlining the WM network. In summary, anodal tDCS caused increased neuronal activation and connectivity, not only in the brain area under the stimulating electrode (i.e. left DLPFC) but also in other, more remote brain regions. Because of moderate behavioral effects of tDCS, the significance of this technique for ADHD treatment has to be investigated in further studies.     

Transcranial direct-current stimulation reduced the excitability of diaphragmatic corticospinal pathways whatever the polarity used

We investigated effects of transcranial direct-current stimulation (tDCS) on the diaphragmatic corticospinal pathways in healthy human. Anodal, cathodal, and sham tDCS were randomly applied upon the left diaphragmatic motor cortex in twelve healthy right-handed men. Corticospinal pathways excitability was assessed by means of transcranial magnetic stimulation (TMS) elicited motor-evoked-potential (MEP). For each tDCS condition, MEPs were recorded before (Pre) tDCS then after 10 min (Post1, at tDCS discontinuation in the anodal and cathodal sessions) and 20 min (Post2). As result, both anodal and cathodal tDCS significantly decreased MEP amplitude of the right hemidiaphragm at both Post1 and Post2, versus Pre. MEP amplitude was unchanged versus Pre during the sham condition. The effects of cathodal and anodal tDCS applied to the diaphragm motor cortex differ from those observed during tDCS of the limb motor cortex. These differences may be related to specific characteristics of the diaphragmatic corticospinal pathways as well as to the diaphragm's functional peculiarities compared with the limb muscles.     

The effect of transcranial direct current stimulation on the cortical activation by motor task in the human brain: An fMRI study

Objectives: We attempted to evaluate whether cortical activation resulting from hand movements is changed by transcranial direct current stimulation (tDCS) applied on the primary motor cortex for the hand in the human brain, using functional MRI (fMRI). Methods: Fourteen normal subjects were recruited; subjects were randomly assigned to either the tDCS group (n = 7) or the sham group (n = 7). fMRI was performed with hand grasp-release movements at 1 Hz before and after 20 min of intervention (the tDCS group: anodal tDCS, the sham group: sham stimulation). Results: The activation of the tDCS underlying primary sensorimotor cortex (SM1) was significantly increased in the tDCS group (p < 0.05). By contrast, the SM1 was significantly decreased in the sham group in terms of the voxel count and intensity (p < 0.05). No subjects complained of any adverse symptoms or signs. Conclusion: We demonstrated that anodal tDCS increased the cortical excitability of the underlying motor cortex in the human brain. It seems that tDCS is an effective modality to modulate brain function.     

Transcranial direct current stimulation effects on I-wave activity in humans

Transcranial direct current stimulation (tDCS) of the human cerebral cortex modulates cortical excitability noninvasively in a polarity-specific manner: anodal tDCS leads to lasting facilitation and cathodal tDCS to inhibition of motor cortex excitability. To further elucidate the underlying physiological mechanisms, we recorded corticospinal volleys evoked by single-pulse transcranial magnetic stimulation of the primary motor cortex before and after a 5-min period of anodal or cathodal tDCS in eight conscious patients who had electrodes implanted in the cervical epidural space for the control of pain. The effects of anodal tDCS were evaluated in six subjects and the effects of cathodal tDCS in five subjects. Three subjects were studied with both polarities. Anodal tDCS increased the excitability of cortical circuits generating I waves in the corticospinal system, including the earliest wave (I1 wave), whereas cathodal tDCS suppressed later I waves. The motor evoked potential (MEP) amplitude changes immediately following tDCS periods were in agreement with the effects produced on intracortical circuitry. The results deliver additional evidence that tDCS changes the excitability of cortical neurons.     

Enhanced locomotor adaptation aftereffect in the "broken escalator" phenomenon using anodal tDCS

The everyday experience of stepping onto a stationary escalator causes a stumble, despite our full awareness that the escalator is broken. In the laboratory, this "broken escalator" phenomenon is reproduced when subjects step onto an obviously stationary platform (AFTER trials) that was previously experienced as moving (MOVING trials) and attests to a process of motor adaptation. Given the critical role of M1 in upper limb motor adaptation and the potential for transcranial direct current stimulation (tDCS) to increase cortical excitability, we hypothesized that anodal tDCS over leg M1 and premotor cortices would increase the size and duration of the locomotor aftereffect. Thirty healthy volunteers received either sham or real tDCS (anodal bihemispheric tDCS; 2 mA for 15 min at rest) to induce excitatory effects over the primary motor and premotor cortex before walking onto the moving platform. The real tDCS group, compared with sham, displayed larger trunk sway and increased gait velocity in the first AFTER trial and a persistence of the trunk sway aftereffect into the second AFTER trial. We also used transcranial magnetic stimulation to probe changes in cortical leg excitability using different electrode montages and eyeblink conditioning, before and after tDCS, as well as simulating the current flow of tDCS on the human brain using a computational model of these different tDCS montages. Our data show that anodal tDCS induces excitability changes in lower limb motor cortex with resultant enhancement of locomotor adaptation aftereffects. These findings might encourage the use of tDCS over leg motor and premotor regions to improve locomotor control in patients with neurological gait disorders.