Combining transcranial direct current stimulation and neuroimaging: novel insights in understanding neuroplasticity

Abstract

In recent years, noninvasive brain stimulation techniques like transcranial direct current stimulation (tDCS) have gained immense popularity owing to their effects on modulating cortical activity and consequently motor and cognitive performance. However, the neurophysiology underlying such neuroplastic changes is less understood. This article critically evaluates the contemporary approach of combined tDCS and neuroimaging as a means to provide novel insights in understanding the neurophysiological and neuroplastic processes modulated by this brain stimulation technique. We end by briefly suggesting further lines of inquiry.

Fig. 1.

A: a schematic summary of transcranial direct current stimulation (tDCS) effects over M1 (bipolar electrode montage with one electrode over M1, and other over contralateral supraorbital region). B: M1 tDCS mediates polarity-specific changes in cortical excitability (shown as motor-evoked potentials, i.e., MEPs expressed as a ratio to baseline) that outlasts duration of stimulation up to 40 min. C also leads to changes in behavior such as motor learning on a serial reaction time task (SRTT). Anodal tDCS over M1 improves motor performance on SRTT more than cathodal and sham tDCS (i.e., greater decrease in reaction time in the early blocks). D: representative cortical brain networks with interacting regional nodes that are likely modulated by tDCS over M1. PFC, prefrontal cortex; SMA, supplementary motor area; PM, premotor cortex; S1, primary somatosensory cortex; M1, primary motor cortex; PPC, posterior parietal cortex. Complex brain network dynamics recorded through neuroimaging could help identify and quantify widespread changes in brain activity and functional connectivity within brain networks to provide more novel insights into neuroplastic mechanisms modulated by tDCS. Note: data shown in graphs are representative of previously published results (Nitsche et al. 2008).