Non-invasive brain stimulation in neurorehabilitation: local and distant effects for motor recovery

Abstract

Non-invasive brain stimulation (NIBS) may enhance motor recovery after neurological injury through the causal induction of plasticity processes. Neurological injury, such as stroke, often results in serious long-term physical disabilities, and despite intensive therapy, a large majority of brain injury survivors fail to regain full motor function. Emerging research suggests that NIBS techniques, such as transcranial magnetic (TMS) and direct current (tDCS) stimulation, in association with customarily used neurorehabilitative treatments, may enhance motor recovery. This paper provides a general review on TMS and tDCS paradigms, the mechanisms by which they operate and the stimulation techniques used in neurorehabilitation, specifically stroke. TMS and tDCS influence regional neural activity underlying the stimulation location and also distant interconnected network activity throughout the brain. We discuss recent studies that document NIBS effects on global brain activity measured with various neuroimaging techniques, which help to characterize better strategies for more accurate NIBS stimulation. These rapidly growing areas of inquiry may hold potential for improving the effectiveness of NIBS-based interventions for clinical rehabilitation.

Keywords: neurorehabilitation; non-invasive brain stimulation; stroke; transcranial direct current stimulation (tDCS); transcranial magnetic stimulation.

Figure 1

NIBS publications. Graph depicting exponential growth in the number of publications on NIBS from 1988 to 2012, with NIBS publications specific to stroke depicted at the top, and NIBS publications specific to stroke shown in the context of the general NIBS field at bottom.

Figure 2

NIBS schematic. Chart depicting the general breakdown of NIBS techniques, focusing on TMS and tES. Types of TMS and tES paradigms are describe, and the divide between physiology and neuromodulatory functions is depicted. Inhibitory and excitatory neuromodulatory techniques are also labeled.

Figure 3

Example of combined tDCS, MEG, and BCI experimental setup. This design uses a 275-sensor whole-head MEG to record neuromagnetic brain activity during tDCS stimulation, with electrodes placed in the classic unilateral M1 montage (anode placed above the area of the right M1 and reference electrode above the left supraorbital area). This set-up is used in conjunction with BCI visual feedback in the form of a computer game and sensorimotor feedback via a robotic hand orthosis that opened as target oscillations increased. Image courtesy of S. Soekadar (Soekadar et al., under review).