Bilateral Transcranial Direct Current Stimulation Modulates Activation-Induced Regional Blood Flow Changes during Voluntary Movement

Abstract

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that induces changes in cortical excitability: anodal stimulation increases while cathodal stimulation reduces excitability. Imaging studies performed after unilateral stimulation have shown conflicting results regarding the effects of tDCS on surrogate markers of neuronal activity. The aim of this study was to directly measure these effects on activation-induced changes in regional cerebral blood flow (DrCBF) using positron emission tomography (PET) during bilateral tDCS. Nine healthy subjects underwent repeated rCBF measurements with 15 O-water and PET during a simple motor task while receiving tDCS or sham stimulation over the primary motor cortex (M1). Motor evoked potentials (MEPs) were also assessed before and after real and sham stimulation. During tDCS with active movement, DrCBF in M1 was significantly lower on the cathodal than the anodal side when compared with sham stimulation. This decrease in DrCBF was accompanied by a decrease in MEP amplitude on the cathodal side. No effect was observed on resting or activated rCBF relative to sham stimulation. We thus conclude that it is the interaction of cathodal tDCS with activation-induced DrCBF rather than the effect on resting or activated rCBF itself which constitutes the physiological imaging correlate of tDCS.

Ceiling Effects Prevent Further Improvement of Transcranial Stimulation in Skilled Musicians

“…Therefore, the actual relevance of anodal versus cathodal stimulation still remains unclear. It seems unlikely that a lack of behavioral changes indicates no neurophysiological changes elicited by the stimulation because previous studies have demonstrated modulation of motor cortical excitability in an opposite direction between the contralateral and ipsilateral sides with bihemispheric tDCS (Paquette et al, 2011;Zheng et al, 2011;Mordillo-Mateos et al, 2012).…”

“…It is also possible that the relation between training and motor cortical excitability forms an inverse U-shape, which may explain our observation of both improvement and deterioration of fine motor control in the pianists and nonmusicians after facilitating stimulation. Indeed, improved motor performance seems to be associated with reduced excitability enhancement after an initial phase of enhanced excitability of the respective area (Pascual-Leone et al, 1994).…”

Excitability modulation of the motor system induced by transcranial direct current stimulation: A multimodal approach

“…To overcome the limitations of this indirect approach, several studies have focused their attention on other neurophysiologic measurements as surrogate markers of tDCS-induced cortical neuromodulatory effects (Brunoni et al, 2011). In this framework, the use of neuroimaging methods, such as functional magnetic resonance (Baudewig et al, 2001;Jang et al, 2009;Kwon et al, 2008;Polania et al, 2012;Stagg et al, 2009a), positron emission tomography Paquette et al, 2011), laser doppler flowmetry (Wachter et al, 2011) and electroencephalography (EEG) (Ardolino et al, 2005;Polania et al, 2010a), have provided further evidence of changes in neural activity induced by tDCS. Moreover, it is understood that, by modulating cortical excitability, tDCS can induce both short-and long-term changes in a polarity-specific manner Paulus, 2001, Nitsche et al, 2003a).…”

Effects of Noninvasive Brain Stimulation on Language Networks and Recovery in Early Poststroke Aphasia

“…[1][2][3] NBS methods, such as conventional repetitive transcranial magnetic stimulation (rTMS), theta burst TMS, or transcranial direct current stimulation, are capable of modulating cortical excitability within a brain region into inhibitory or excitatory direction using either magnetic or electric fields. These effects are foremost local insofar as they directly affect the cortex at the stimulation site, 4 but if the stimulated region constitutes a node within a larger network (eg, human language networks), activity within the entire network might be affected indirectly. 5,6 The effects of NBS on disturbed language networks are not yet fully understood, and various mechanisms have been postulated to explain the compensation of focal disturbances within the functional networks by excitatory or inhibitory effects on different brain regions.…”