Polarity-specific effects of motor transcranial direct current stimulation on fMRI resting state networks

Abstract

Transcranial direct current stimulation (tDCS) has been used to modify motor performance in healthy and patient populations. However, our understanding of the large-scale neuroplastic changes that support such behavioural effects is limited. Here, we used both seed-based and independent component analyses (ICA) approaches to probe tDCS-induced modifications in resting state activity with the aim of establishing the effects of tDCS applied to the primary motor cortex (M1) on both motor and non-motor networks within the brain. Subjects participated in three separate sessions, during which resting fMRI scans were acquired before and after 10 min of 1 mA anodal, cathodal, or sham tDCS. Cathodal tDCS increased the inter-hemispheric coherence of resting fMRI signal between the left and right supplementary motor area (SMA), and between the left and right hand areas of M1. A similar trend was documented for the premotor cortex (PMC). Increased functional connectivity following cathodal tDCS was apparent within the ICA-generated motor and default mode networks. Additionally, the overall strength of the default mode network was increased. Neither anodal nor sham tDCS produced significant changes in resting state connectivity. This work indicates that cathodal tDCS to M1 affects the motor network at rest. In addition, the effects of cathodal tDCS on the default mode network support the hypothesis that diminished top-down control may contribute to the impaired motor performance induced by cathodal tDCS.

Direct Current Stimulation Alters Neuronal Input/Output Function

“…Until recently [12], the argument typically focused on somatic polarization of pyramidal cells, and tended to ignore the simultaneous opposite polarization of apical dendritites. The more detailed analysis provided here for the interaction of these two effects provides a possible explanation for the numerous findings that anodal and cathodal effects are not of equal strength in many human and animal studies [18]–[20], [24], [74], anodal often having a stronger effect [21]–[23], [25], [26]. The computational model suggests that the region under the anode has increased excitability, with a higher likelihood of firing for a given synaptic input.…”

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…However, in elderly atDCS seems to decrease FC of motor network suggesting a differential effect of atDCS due to age [29, 30], although the behavioral significance of these changes is not yet clear. The relationship between ctDCS and functional changes is also unclear, since variables effects have been reported to date (i.e., no change, increased, decreased FC) [28-30, 34]. …”

Understanding the behavioural consequences of noninvasive brain stimulation

“…Moreover, evidence from in vivo recording [20,21] and human neuroimaging [22][23][24][25][26][27] studies suggests that tES effects are not constrained to the cortex underneath an electrode. Simulations of current flow in the brain suggest a widespread and complex distribution of induced currents [28][29][30] that can expose both cortical and subcortical regions to currents of sufficient intensity to affect neural activity.…”