Absolute gobbledegook written here. Useless. There is no way I could take this to any doctor or therapist and explain what needs to be done and the results expected from this intervention.
Neurophysiological signatures of hand motor response to dual-transcranial direct current stimulation in subacute stroke: a TMS and MEG study
Abstract
Background
Dual transcranial direct current stimulation (tDCS) to the bilateral primary motor cortices (M1s) has potential benefits in chronic stroke, but its effects in subacute stroke, when behavioural effects might be expected to be greater, have been relatively unexplored. Here, we examined the neurophysiological effects and the factors influencing responsiveness of dual-tDCS in subacute stroke survivors.Methods
We conducted a randomized sham-controlled crossover study in 18 survivors with first-ever, unilateral subcortical ischaemic stroke 2–4 weeks after stroke onset and 14 matched healthy controls. Participants had real dual-tDCS (with an ipsilesional [right for controls] M1 anode and a contralesional M1 [left for controls] cathode; 2 mA for 20mins) and sham dual-tDCS on separate days, with concurrent paretic [left for controls] hand exercise. Using transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG), we recorded motor evoked potentials (MEPs), the ipsilateral silent period (iSP), short-interval intracortical inhibition, and finger movement-related cortical oscillations before and immediately after tDCS.Results
Stroke survivors had decreased excitability in ipsilesional M1 with a relatively excessive transcallosal inhibition from the contralesional to ipsilesional hemisphere at baseline compared with controls, as quantified by decreased MEPs and increased iSP duration. Dual-tDCS led to increased MEPs and decreased iSP duration in ipsilesional M1. The magnitude of the tDCS-induced MEP increase in stroke survivors was predicted by baseline contralesional-to-ipsilesional transcallosal inhibition (iSP) ratio. Baseline post-movement synchronization in α-band activity in ipsilesional M1 was decreased after stroke compared with controls, and its tDCS-induced increase correlated with upper limb score in stroke survivors. No significant adverse effects were observed during or after dual-tDCS.Conclusions
Task-concurrent dual-tDCS in subacute stroke can safely and effectively modulate bilateral M1 excitability and inter-hemispheric imbalance and also movement-related α-activity.Background
Transcranial
direct current stimulation (tDCS) has been demonstrated to
non-invasively modulate cortical excitability in the primary motor
cortex (M1) in both controls and stroke survivors [1, 2].
Motor evoked potentials (MEPs) typically increase following unilateral
anodal tDCS and decrease following unilateral cathodal tDCS, with
effects outlasting stimulation by minutes to hours [3].
This polarity-specific modulation has been suggested as a putative way
to promote post-stroke motor recovery, either by enhancing ipsilesional
M1 excitability with anodal tDCS or decreasing contralesional M1
excitability with cathodal tDCS [4].
Some tDCS studies have suggested that these approaches may be
promising, but the quality of evidence for tDCS in promoting post-stroke
motor recovery is still low to moderate [5],
partially due to heterogeneity in study designs and stroke survivor
profiles across the literature, and small sample sizes within studies [6].
To successfully translate tDCS effects into clinical benefits, patient
selection based on neurophysiological status for a given effective tDCS
montage may be required [6,7,8,9].
Dual, or bi-hemispheric, tDCS involves concurrent anodal stimulation to one M1 and cathodal stimulation to the other M1. The effects of dual tDCS have been studied in both healthy controls and stroke survivors in a number of different ways. Dual-tDCS has been shown to have a significant beneficial effect in dexterity [10] and motor learning [11,12,13,14] in controls. The effects of dual-tDCS on motor performance were better or at least equal to the unilateral anodal stimulation effect in most of these studies [10, 11, 13, 14]. Consistent with these behavioural findings, increased MEPs in the anode-targeted M1 and decreased MEPs in the cathode-targeted M1 after dual-tDCS have been demonstrated in most studies in healthy controls [10, 14,15,16,17], suggesting that dual-tDCS may result in additive effects of unilateral stimulation, although these effects are not entirely consistent [18].
The effects of dual-tDCS post stroke, when an ipsilesional anode and a contralesional cathode have been paired with concurrent rehabilitation, are much more varied across studies, with some studies demonstrating significantly enhanced motor score, dexterity or grip strength [19,20,21,22,23] in chronic stroke survivors, but other studies showing no effect [24,25,26]. Only one previous study has explored the immediate post-stimulation effects of dual-tDCS on cortical excitability, which showed no significant changes in MEPs or transcallosal inhibition in six subacute stroke survivors [27]. Two studies have combined repetitive dual-tDCS with rehabilitation in chronic stroke survivors and demonstrated an increase in ipsilesional MEPs compared to sham [19, 20]. Sensorimotor dynamic activity, recorded using electroencephalography (EEG) or magnetoencephalography (MEG), are also altered following stroke [28,29,30,31], and changes in these measures are correlated with motor function [30, 31]. The event-related desynchronization (ERD) before and during movement has been associated with motor preparation and execution, while event-related synchronization (ERS) after cessation of movement has been suggested to reflect motor deactivation [32]. Dual-tDCS has been shown to alter motor imagery-related hemispheric lateralization in sensorimotor rhythms in controls [33] and after stroke [34]. However, the effect of dual-tDCS on movement-related dynamic activity has not yet been examined.
We hypothesized that task-concurrent dual-tDCS could enhance ipsilesional corticospinal excitability, modulate movement-related brain oscillations, and also rebalance the asymmetry of interhemispheric interactions after subacute stroke. Potential for recovery is most prominent early after stroke and declines gradually after 6 months (chronic stage) [35, 36]. Most rehabilitation intervention studies, including tDCS studies, recruit patients at the chronic stage of recovery [37], but it is likely that rehabilitative effects would be stronger if applied earlier. In addition, recent studies have also demonstrated that different adaptive mechanisms and bi-hemispheric interactions may exist during the subacute and chronic stages [38, 39]. Studying effects in subacute stroke is therefore important if we are to fully explore the potential of dual-tDCS for stroke recovery. Cortical and subcortical infarctions have highly different outcomes, network reorganization and tDCS responsiveness [22]. To minimize variations in tDCS substrates (the cortex) and responsiveness in this study, we enrolled stroke survivors with relatively homogenous subcortical infarctions at 2–4 weeks post-stroke to investigate the effects of dual-tDCS using transcranial magnetic stimulation (TMS) and MEG in a randomized, sham-controlled, crossover study design to compare the effects of dual-tDCS in subacute stroke survivors and age- and gender-matched controls, as well as explore factors predicting responsiveness to dual-tDCS.
Dual, or bi-hemispheric, tDCS involves concurrent anodal stimulation to one M1 and cathodal stimulation to the other M1. The effects of dual tDCS have been studied in both healthy controls and stroke survivors in a number of different ways. Dual-tDCS has been shown to have a significant beneficial effect in dexterity [10] and motor learning [11,12,13,14] in controls. The effects of dual-tDCS on motor performance were better or at least equal to the unilateral anodal stimulation effect in most of these studies [10, 11, 13, 14]. Consistent with these behavioural findings, increased MEPs in the anode-targeted M1 and decreased MEPs in the cathode-targeted M1 after dual-tDCS have been demonstrated in most studies in healthy controls [10, 14,15,16,17], suggesting that dual-tDCS may result in additive effects of unilateral stimulation, although these effects are not entirely consistent [18].
The effects of dual-tDCS post stroke, when an ipsilesional anode and a contralesional cathode have been paired with concurrent rehabilitation, are much more varied across studies, with some studies demonstrating significantly enhanced motor score, dexterity or grip strength [19,20,21,22,23] in chronic stroke survivors, but other studies showing no effect [24,25,26]. Only one previous study has explored the immediate post-stimulation effects of dual-tDCS on cortical excitability, which showed no significant changes in MEPs or transcallosal inhibition in six subacute stroke survivors [27]. Two studies have combined repetitive dual-tDCS with rehabilitation in chronic stroke survivors and demonstrated an increase in ipsilesional MEPs compared to sham [19, 20]. Sensorimotor dynamic activity, recorded using electroencephalography (EEG) or magnetoencephalography (MEG), are also altered following stroke [28,29,30,31], and changes in these measures are correlated with motor function [30, 31]. The event-related desynchronization (ERD) before and during movement has been associated with motor preparation and execution, while event-related synchronization (ERS) after cessation of movement has been suggested to reflect motor deactivation [32]. Dual-tDCS has been shown to alter motor imagery-related hemispheric lateralization in sensorimotor rhythms in controls [33] and after stroke [34]. However, the effect of dual-tDCS on movement-related dynamic activity has not yet been examined.
We hypothesized that task-concurrent dual-tDCS could enhance ipsilesional corticospinal excitability, modulate movement-related brain oscillations, and also rebalance the asymmetry of interhemispheric interactions after subacute stroke. Potential for recovery is most prominent early after stroke and declines gradually after 6 months (chronic stage) [35, 36]. Most rehabilitation intervention studies, including tDCS studies, recruit patients at the chronic stage of recovery [37], but it is likely that rehabilitative effects would be stronger if applied earlier. In addition, recent studies have also demonstrated that different adaptive mechanisms and bi-hemispheric interactions may exist during the subacute and chronic stages [38, 39]. Studying effects in subacute stroke is therefore important if we are to fully explore the potential of dual-tDCS for stroke recovery. Cortical and subcortical infarctions have highly different outcomes, network reorganization and tDCS responsiveness [22]. To minimize variations in tDCS substrates (the cortex) and responsiveness in this study, we enrolled stroke survivors with relatively homogenous subcortical infarctions at 2–4 weeks post-stroke to investigate the effects of dual-tDCS using transcranial magnetic stimulation (TMS) and MEG in a randomized, sham-controlled, crossover study design to compare the effects of dual-tDCS in subacute stroke survivors and age- and gender-matched controls, as well as explore factors predicting responsiveness to dual-tDCS.
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