Transcranial Direct Current Stimulation for Poststroke Motor Recovery: Challenges and Opportunities

Abstract

There has been a renewed research interest in transcranial direct current stimulation (tDCS) as an adjunctive tool for poststroke motor recovery as it has a neuro‐modulatory effect on the human cortex. However, there are barriers towards its successful application in motor recovery as several scientific issues remain unresolved, including device‐related issues (ie, dose‐response relationship, safety and tolerability concerns, interhemispheric imbalance model, and choice of montage) and clinical trial‐related issues (ie, patient selection, timing of study, and choice of outcomes). This narrative review examines and discusses the existing challenges in using tDCS as a brain modulation tool in facilitating recovery after stroke. Potential solutions pertinent to using tDCS with the goal of harnessing the brains plasticity are proposed.

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

“…The modulation of excitability, measured during or acutely after stimulation, and plasticity based on markers of LTP or long-term monitoring, are related. The application of tDCS in neurorehabilitation is not surprising, since it can be used to increase or decrease brain function and learning [47–50], and it is considered safe and well-tolerated [51, 52]. Evidence from DCS clinical trials is further supported by animal models of injury recovery [39, 53–57].…”

“…Based on the model of post-stroke abnormal interhemispheric inhibition [134, 135], three different montages of stimulation to improve motor recovery are commonly used: anodal tDCS (a-tDCS) over the ipsilesional hemisphere, cathodal tDCS (c-tDCS) over the contralesional hemisphere, and dual tDCS where the anode is placed over ipsilesional and cathode over contralesional hemisphere simultaneously [17, 47, 52]. These three montages are supposed to help to normalize the balance of transcallosal inhibition between both hemispheres resulting in improved motor function [136].…”

“…Currently, there is insufficient evidence for recommending specific targeted cerebral areas, stroke phase, type of combined therapy and order of stimulation/therapy application for all patients. The magnitude of tDCS effect on stroke motor recovery appears to be influenced by multiple factors such as stroke severity and chronicity, lesion size and location, and cortical tract integrity [52, 166]. Future research should focus on developing the personalized tDCS protocol based on individual patient factors to lead to better motor recovery.…”

Dose-controlled tDCS reduces electric field intensity variability at a cortical target site

“…1 or 2mA) across individuals ignores how much current actually reaches the brain in a given individual. This "one-size-fits-all" approach results in substantial variation in E-fields in cortex [20,23].…”

“…T1-weighted structural MRIs from 50 randomly selected healthy adults (aged[22][23][24][25][26][27][28][29][30][31][32][33][34][35]23 males, 27 females) were obtained from the Human Connectome Project (HCP) database(https://ida.loni.usc.edu/login.jsp). Images were acquired from a 3.0 T Siemens Connectome Skyra scanner using a standard 32 channel Siemens receiver head coil.…”