Combining transcranial direct current stimulation with aerobic exercise to optimize cortical priming in stroke

Abstract

Aerobic exercise (AE) and transcranial direct current stimulation (tDCS) are priming techniques that have been studied for their potential neuromodulatory effects on corticomotor excitability (CME); however, the synergistic effects of AE and tDCS are not explored in stroke. Here we investigated the synergistic effects of AE and tDCS on CME, intracortical and transcallosal inhibition, and motor control for the lower limb in stroke. Twenty-six stroke survivors participated in 3 sessions: tDCS, AE, and AE+tDCS. AE included moderate-intensity exercise and tDCS included 1 mA of anodal tDCS to the lower limb motor cortex with or without AE. Outcomes included measures of CME, short-interval intracortical inhibition (SICI), ipsilateral silent period (iSP) (an index of transcallosal inhibition) for the tibialis anterior, and ankle reaction time. Ipsilesional CME significantly decreased for AE compared with AE+tDCS and tDCS. No differences were noted in SICI, iSP measures, or reaction time between all 3 sessions. Our findings suggest that a combination of exercise and tDCS, and tDCS demonstrate greater excitability of the ipsilesional hemisphere compared with exercise only; however, these effects were specific to the descending corticomotor pathways. No additive priming effects of exercise and tDCS over tDCS was observed. Novelty: An exercise and tDCS paradigm upregulated the descending motor pathways from the ipsilesional lower limb primary motor cortex compared with exercise. Exercise or tDCS administered alone or in combination did not affect intracortical or transcallosal inhibition or reaction time.

Keywords: aerobic exercise; amorçage cortical; cortical priming; corticomotor excitability; excitabilité corticomotrice; exercice aérobie; reaction time; stimulation transcrânienne en courant continu; temps de réaction; tibial antérieur; tibialis anterior; transcranial direct current stimulation.

Figures

Figure 1.

Study design schematic. Abbreviations: FMLE, Fugl-Meyer lower extremity; TMS, transcranial magnetic stimulation; RT, reaction time; AE, aerobic exercise; tDCS, transcranial direct current stimulation; AE, aerobic exercise; SICI, short interval intracortical inhibition; TCI, transcallosal inhibition.

Figure 2.

Schematic of electromyographic data representing short interval intracortical inhibition (SICI) and transcallosal inhibition (TCI). The left panel (A) shows SICI obtained with contralateral stimulation of the ipsilesional M1. Unconditioned [blue, test stimulus (TS)] and conditioned [red, conditioning stimulus (CS) + TS] average raw motor evoked potential (MEP) traces obtained from the ipsilesional hemisphere (lesioned area in brown) from a representative subject. The right panel (B) shows an overlaid raw ipsilateral silent period (iSP) trace obtained with ipsilateral stimulation from a representative subject. The black line represents the averaged trace while the light grey lines represent individual traces. Stimulation of the ipsilesional motor cortex inhibits (−) the corticomotor drive from the active contralesional motor cortex via transcallosal pathways.

Figure 3.

Change in area under the curve (AUC) following transcranial direct current stimulation (tDCS, blue), aerobic exercise (AE, cyan) and AE + tDCS (orange) for contralesional and ipsilesional hemispheres. Bars are depicted as mean ± standard error. ** Indicates statistically significant differences (p

Figure 4.

Distribution of responders (green) and non-responders (pink) across following transcranial direct current stimulation (tDCS), aerobic exercise (AE) and AE + tDCS sessions.

Figure 5.

Relationship between baseline short interval intracortical inhibition (SICI) and response to AE + tDCS session (normalized area under the curve AUC). The figures show significant positive correlations between baseline SICI2ms and AUC (red), and baseline SICI3ms and AUC (blue) respectively. Note that higher values of SICI represent higher intracortical inhibition and higher values of AUC represent higher corticomotor excitability.