Transcranial Direct Current Stimulation Over the Primary and Secondary Somatosensory Cortices Transiently Improves Tactile Spatial Discrimination in Stroke Patients

Abstract

In healthy subjects, dual hemisphere transcranial direct current stimulation (tDCS) over the primary (S1) and secondary somatosensory cortices (S2) has been found to transiently enhance tactile performance. However, the effect of dual hemisphere tDCS on tactile performance in stroke patients with sensory deficits remains unknown. The purpose of this study was to investigate whether dual hemisphere tDCS over S1 and S2 could enhance tactile discrimination in stroke patients. We employed a double-blind, crossover, sham-controlled experimental design. Eight chronic stroke patients with sensory deficits participated in this study. We used a grating orientation task (GOT) to measure the tactile discriminative threshold of the affected and non-affected index fingers before, during, and 10 min after four tDCS conditions. For both the S1 and S2 conditions, we placed an anodal electrode over the lesioned hemisphere and a cathodal electrode over the opposite hemisphere. We applied tDCS at an intensity of 2 mA for 15 min in both S1 and S2 conditions. We included two sham conditions in which the positions of the electrodes and the current intensity were identical to that in the S1 and S2 conditions except that current was delivered for the initial 15 s only. We found that GOT thresholds for the affected index finger during and 10 min after the S1 and S2 conditions were significantly lower compared with each sham condition. GOT thresholds were not significantly different between the S1 and S2 conditions at any time point. We concluded that dual-hemisphere tDCS over S1 and S2 can transiently enhance tactile discriminative task performance in chronic stroke patients with sensory dysfunction.

Investigating the Effects of tDCS on Visual Orientation Discrimination Task Performance: “the Possible Influence of Placebo”

“…Such perceptual judgments often depend on inhibition between primary sensory representations in cortex and thus tasks of this nature, maybe more easily be altered by tDCS than those requiring higher cognitive regions where the link between E-I balance and performance is less easy to intuit. Indeed, tDCS has been shown to alter somatosensory discrimination (Fujimoto et al 2016;Labbé et al 2016) and auditory pitch discrimination (Mathys et al 2010). Surprisingly, as far as we are aware, no authors have investigated whether tDCS can alter performance on a visual ODT, a task with clear links to E-I balance in cortex.…”

Physical Therapy for Cerebellar Ataxia

“…NIBS, which is repetitive TMS (rTMS) [96,98] and transcranial direct current stimulation (tDCS) [124], over the primary motor cortex can modulate the excitability of the motor cortex [125] and is often used as an effective tool for enhancing behavioral training after stroke with hemiplegia [125][126][127][128]. Furthermore, the NIBS to the cerebellum modulates cerebellar excitability [98,[129][130][131], motor function [132,133], and motor learning [32,[134][135][136][137][138] in healthy population.…”

Effects of tDCS on tactile perception in musicians and non-musicians

“…In other studies, contralateral c-tDCS reduced sensitivity to hot and cold sensations [16], decreased pain perception thresholds [17], and decrease tactile discrimination performance [18]. In a recent study, the tactile discrimination threshold of stroke patients was measured by GOT and it was shown that dual-hemispheric tDCS improved performance in comparison to a sham stimulation group [15] Similarly, low current a-tDCS over S1 of healthy young adults enhanced contralateral index finger discrimination performance in GOT, with no such effects in the s-tDCS condition [12].…”

“…Positively charged stimulation, which causes depolarization of superficial cortical neurons, is named anodal-tDCS (a-tDCS) and negatively charged stimulation, which causes hyperpolarization, is named cathodal-tDCS (c-tDCS) [11]. Sham-tDCS (s-tDCS) is often used to control for the experimental setup itself both in applied [12] and clinical [13] research, but findings are ambivalent: while in some studies s-tDCS does not provide different results from active stimulations, which serves as evidence for a placebo effect [14], in other studies s-tDCS produces different results, refuting a placebo effect [15].…”