Anodal Transcranial Direct Current Stimulation Increases Bilateral Directed Brain Connectivity during Motor-Imagery Based Brain-Computer Interface Control

Abstract

Transcranial direct current stimulation (tDCS) has been shown to affect motor and cognitive task performance and learning when applied to brain areas involved in the task. Targeted stimulation has also been found to alter connectivity within the stimulated hemisphere during rest. However, the connectivity effect of the interaction of endogenous task specific activity and targeted stimulation is unclear. This study examined the aftereffects of concurrent anodal high-definition tDCS over the left sensorimotor cortex with motor network connectivity during a one-dimensional EEG based sensorimotor rhythm brain-computer interface (SMR-BCI) task. Directed connectivity following anodal tDCS illustrates altered connections bilaterally between frontal and parietal regions, and these alterations occur in a task specific manner; connections between similar cortical regions are altered differentially during left and right imagination trials. During right-hand imagination following anodal tDCS, there was an increase in outflow from the left premotor cortex (PMC) to multiple regions bilaterally in the motor network and increased inflow to the stimulated sensorimotor cortex from the ipsilateral PMC and contralateral sensorimotor cortex. During left-hand imagination following anodal tDCS, there was increased outflow from the stimulated sensorimotor cortex to regions across the motor network. Significant correlations between connectivity and the behavioral measures of total correct trials and time-to-hit (TTH) correct trials were also found, specifically that the input to the left PMC correlated with decreased right hand imagination performance and that flow from the ipsilateral posterior parietal cortex (PPC) to midline sensorimotor cortex correlated with improved performance for both right and left hand imagination. These results indicate that tDCS interacts with task-specific endogenous activity to alter directed connectivity during SMR-BCI. In order to predict and maximize the targeted effect of tDCS, the interaction of stimulation with the dynamics of endogenous activity needs to be examined comprehensively and understood.

tDCS targeting the Ventromedial Prefrontal Cortex reduces reactive aggression and modulates electrophysiological responses: A HD-tDCS/EEG randomized controlled trial in a forensic population.

“…To date, the majority of the studies that investigate the modulation of the PFC have relied on conventional tDCS, upregulating one side of the brain and downregulating the contralateral region [66]. Our study uses a developed protocol using high-definition tDCS (HD-tDCS) targeting the vmPFC, with multiple sessions and a focus on enhancing the brain state during modulation to maximize the effect [67][68][69][70].…”

Transcranial electrical stimulation (tES) mechanisms and its effects on cortical excitability and connectivity

“…In addition, they showed that changes in connectivity were higher during the motor task than at rest. Task-related connectivity changes have been demonstrated in a wide variety of other tasks, including risk taking (Weber et al 2014 ), on a sensorimotor rhythm brain computer interface task (Baxter et al 2017 ), a smoking cue reactivity task (Yang et al 2017 ) and during speech (Holland et al 2016 ). Examination of glutamatergic neurotransmission during anodal tDCS using proton magnetic resonance spectroscopy (MRS) found that glutamate and glutamine concentrations (Glx) were increased under the anodal electrode, and individual differences in Glx predicted network connectivity (Hunter et al 2015 ) and remote effects on brain regions that were not directly beneath the electrodes (Hone-Blanchet et al 2016 ).…”

Functional Brain Connectivity during Multiple Motor Imagery Tasks in Spinal Cord Injury

“…The degree that each factor possibly contributed to this finding is an issue for further investigation. An example of SMAs and primary motor areas not presenting the greatest strength during hands motor imagery has also been recently reported in a study [ 97 ] where the authors used transcranial direct current stimulation to affect the connectivity of a broader definition of sensorimotor ROIs.…”