Does anodal transcranial direct current stimulation enhance excitability of the motor cortex and motor function in healthy individuals and subjects with stroke: A systematic review and meta-analysis

Department of Physiotherapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Australia.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology (Impact Factor: 3.1). 04/2012; 123(4):644-57. DOI: 10.1016/j.clinph.2011.08.029
Source: PubMed


The primary aim of this review is to evaluate the effects of anodal transcranial direct current stimulation (a-tDCS) on corticomotor excitability and motor function in healthy individuals and subjects with stroke. The secondary aim is to find a-tDCS optimal parameters for its maximal effects. Electronic databases were searched for studies into the effect of a-tDCS when compared to no stimulation. Studies which met the inclusion criteria were assessed and methodological quality was examined using PEDro and Downs and Black (D&B) assessment tools. Data from seven studies revealed increase in corticomotor excitability with a small but significant effect size (0.31 [0.14, 0.48], p=0.0003) in healthy subjects and data from two studies in subjects with stroke indicated significant results with moderate effect size (0.59 [0.24, 0.93], p=0.001) in favor of a-tDCS. Likewise, studies examining motor function demonstrated a small and non-significant effect (0.39 [-0.17, 0.94], p=0.17) in subjects with stroke and a large but non-significant effect (0.92 [-1.02, 2.87], p=0.35) in healthy subjects in favor of improvement in motor function. The results also indicate that efficacy of a-tDCS is dependent on current density and duration of application. A-tDCS increases corticomotor excitability in both healthy individuals and subjects with stroke. The results also show a trend in favor of motor function improvement following a-tDCS. A-tDCS is a non-invasive, cheap and easy-to-apply modality which could be used as a stand-alone technique or as an adds-on technique to enhance corticomotor excitability and the efficacy of motor training approaches. However, the small sample size of the included studies reduces the strength of the presented evidences and any conclusion in this regard should be considered cautiously.

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    • "In such case, anodal tDCS applied over the ipsilateral motor cortex could be an interesting strategy to optimize muscle performance in healthy subjects, as previously demonstrated (Boggio et al., 2006b). Another possible strategy to optimize the leg muscle performance would be to amplify the electrical current density (μA/cm 3 ) under the active electrodes (McCreery, Agnew, Yuen, & Bullara, 1990) or to increase the duration of tDCS stimulus, in order to promote more effective changes in the corticomotor excitation, responsible to recruit motor units of major muscles groups in the lower limbs (Bastani & Jaberzadeh, 2012). Finally, the anodal tDCS could be applied during (and not prior to) the exercise performed until fatigue, since there is preliminary evidence demonstrating that anodal tDCS would be effective to bolster the capacity to exercise under such conditions (Williams et al., 2013). "

    Full-text · Article · Sep 2015 · Isokinetics and exercise science
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    • "Furthermore, inter-study variability in stimulation parameters such as current density and stimulation duration, both of which are known moderators of tDCS dose [46] [47], also likely contributes to the disparity in results observed thus far. Available neurophysiological data from studies of the motor cortex show some support for a dose–response relationship between cortico-spinal excitability and either current density or stimulation duration, whereby, within specific limits, larger current densities or longer stimulation durations lead to more pronounced excitability changes [26] [48] [49]. However, these results are certainly not without exception [33] [50] [51] and whether any such relationship can be extended to stimulation of other brain regions, or to cognitive/behavioural outcome measures, remains to be established, with inconsistent findings having been reported thus far [11] [16] [52] [53]. "
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    ABSTRACT: AbstractBackground Several studies have trialled anodal transcranial direct current stimulation (a-tDCS) for the enhancement of working memory (WM) in both healthy and neuropsychiatric populations. However, the efficacy of this technique remains to be clearly established. Objective This review provides a quantitative synthesis of the published literature investigating the effects of a-tDCS, compared to sham, on WM, as assessed using the n-back, Sternberg and digit-span tasks. We also separated results from tasks performed ‘online’ (during stimulation) and ‘offline’ (following stimulation). The secondary aim was to assess for any additional effects of current density and stimulation duration. Methods Comprehensive literature searches were performed using MEDLINE, Embase, PsychINFO, CENTRAL and Scopus from July 1998 to June 2014. Results In healthy cohorts, a-tDCS produced a trend towards improvement for offline WM accuracy (p = 0.05) and a small, but significant improvement in reaction time (p = 0.04); however, no significant effects were observed for online tasks (accuracy [p = 0.29], reaction time [p = 0.42]). In the neuropsychiatric cohort, a-tDCS significantly improved accuracy for online (p = 0.003), but not offline (p = 0.87) tasks, and no effect was seen for either online (p = 0.20) or offline (p = 0.49) reaction times. Secondary analyses controlling for current density and stimulation duration provided limited support for the role of these factors in influencing a-tDCS efficacy. Conclusions This review provides some evidence of a beneficial effect of a-tDCS on WM performance. However, the small effect sizes obtained, coupled with non-significant effects on several analyses require cautious interpretation and highlight the need for future research aimed at investigating more optimised stimulation approaches.
    Full-text · Article · Jan 2015 · Brain Stimulation
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    • "of stimulation [28] [29]. When applied to the motor cortex, which is accompanied by the contraction of muscles, TMS can alter the heart rate variability (HRV) due to connections between the brain cortex and the autonomic centers [30] [31]. "
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    ABSTRACT: Several standard protocols based on repetitive transcranial magnetic stimulation (rTMS) have been employed for treatment of a variety of neurological disorders. Despite their advantages in patients that are retractable to medication, there is a lack of knowledge about the effects of rTMS on the autonomic nervous system that controls the cardiovascular system. Current understanding suggests that the shape of the so-called QRS complex together with the size of the different segments and intervals between the PQRST deflections of the heart could predict the nature of the different arrhythmias and ailments affecting the heart. This preliminary study involving 10 normal subjects from 20 to 30 years of age demonstrated that rTMS can induce changes in the heart rhythm. The autonomic activity that controls the cardiac rhythm was indeed altered by an rTMS session targeting the motor cortex using intensity below the subject's motor threshold and lasting no more than 5 minutes. The rTMS activation resulted in a reduction of the RR intervals (cardioacceleration) in most cases. Most of these cases also showed significant changes in the Poincare plot descriptor SD2 (long-term variability), the area under the low frequency (LF) power spectrum density curve, and the low frequency to high frequency (LF/HF) ratio. The RR intervals changed significantly in specific instants of time during rTMS activation showing either heart rate acceleration or heart rate deceleration.
    Full-text · Article · Jul 2014
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