Searching for the optimal tDCS target for motor rehabilitation

Abstract

Background Transcranial direct current stimulation (tDCS) has been investigated over the years due to its short and also long-term effects on cortical excitability and neuroplasticity. Although its mechanisms to improve motor function are not fully understood, this technique has been suggested as an alternative therapeutic method for motor rehabilitation, especially those with motor function deficits. When applied to the primary motor cortex, tDCS has shown to improve motor function in healthy individuals, as well as in patients with neurological disorders. Based on its potential effects on motor recovery, identifying optimal targets for tDCS stimulation is essential to improve knowledge regarding neuromodulation as well as to advance the use of tDCS in clinical motor rehabilitation. Methods and results Therefore, this review discusses the existing evidence on the application of four different tDCS montages to promote and enhance motor rehabilitation: (1) anodal ipsilesional and cathodal contralesional primary motor cortex tDCS, (2) combination of central tDCS and peripheral electrical stimulation, (3) prefrontal tDCS montage and (4) cerebellar tDCS stimulation. Although there is a significant amount of data testing primary motor cortex tDCS for motor recovery, other targets and strategies have not been sufficiently tested. This review then presents the potential mechanisms and available evidence of these other tDCS strategies to promote motor recovery. Conclusions In spite of the large amount of data showing that tDCS is a promising adjuvant tool for motor rehabilitation, the diversity of parameters, associated with different characteristics of the clinical populations, has generated studies with heterogeneous methodologies and controversial results. The ideal montage for motor rehabilitation should be based on a patient-tailored approach that takes into account aspects related to the safety of the technique and the quality of the available evidence.

Bilateral Motor Cortex tDCS Effects on Post-Stroke Pain and Spasticity: A Three Cases Study

“…These effects were verbally mentioned by the three patients in both stimulation conditions, i.e., anodal and sham tDCS. This good tolerability is in accordance with the known excellent safety profile of tDCS ( Brunoni et al, 2012 ; Bikson et al, 2016 ; Woods et al, 2016 ; Antal et al, 2017 ; Jackson et al, 2017a ; Jackson et al, 2017b ), which is also an important factor to consider this method for treatment in post-stroke patients ( Stagg et al, 2012 ; Gomez Palacio Schjetnan et al, 2013 ; O’Shea et al, 2014 ; Fregni et al, 2015 ; Allman et al, 2016 ; Santos Ferreira et al, 2019 ).…”

Effects of Transcranial Direct Current Stimulation Combined With Physical Training on the Excitability of the Motor Cortex, Physical Performance, and Motor Learning: A Systematic Review

“…Studies have shown tDCS itself holds great promise to improve functional performance and help in rehabilitative medicine field via the facilitation and modulation of cortical excitability and plasticity (Santos Ferreira et al, 2019). However, large interpersonal variability in the effects of tDCS is observed due to the variance in the protocol of using tDCS, including the electrode position, dose (current intensity and duration), and differences in the brain structure across people (e.g., skull thickness, subcutaneous fat levels, cerebrospinal fluid density, cortical surface topography, age, gender, and genetics) (Wiethoff et al, 2014).…”

Gait and Functional Mobility in Multiple Sclerosis: Immediate Effects of Transcranial Direct Current Stimulation (tDCS) Paired With Aerobic Exercise

“…Specific electrode montages have varied across studies aimed at improving motor performance and symptoms to date, but most of them applied the anode over M1 area (34)(35)(36). Some studies conceptualized alternative motor electrode montages, varying electrode dimensions, and the position of the cathode, in order to optimize the stimulation of the lower limb motor cortex (37,38).…”