Background: Cortical priming is a promising adjuvant to conventional rehabilitation that can be used to facilitate neuroplasticity and improve behavioral outcomes. Acute aerobic exercise (AE) and transcranial direct current stimulation (tDCS) are priming tools that have shown individual effects on corticomotor excitability and motor skill learning in healthy individuals and stroke. Although the utility of tDCS has been demonstrated in combination with other motor tasks, the neurophysiological effects of a combination of acute aerobic exercise and tDCS on the lower limb M1 are unknown. Here, we sought to investigate the effects of a combination of aerobic exercise and tDCS on corticomotor excitability, intracortical and transcallosal inhibition and motor function for the lower limb in stroke.
Methods: In this cross over study individals with stroke underwent imental sessions i.e. aerobic exercise training (AE) + tDCS, AE and tDCS-only conditions. The exercise conditions included moderate intensity (50 – 65% of heart rate maximum) exercise on a recumbent stepper (25 minutes total, 5 minutes warm up and cool down). Anodal tDCS was administered to the lesioned lower limb M1. Electromyography data was obtained from bilateral tibialis anterior muscles in response to single pulse and paired pulse transcranial magnetic stimulation (TMS). Outcomes included TMS measures of area under the recruitment curve (AURC) recorded from intensities corresponding to 80% – 140% active motor threshold, short interval intracortical inhibition (SICI), ipsilateral silent period (iSP) (an index of transcallosal inhibition (TCI)) and reaction time before and after each condition. SICI and TCI were also measured 30 minutes after each condition.
Results: Three individuals withdrew from the study due to personal reasons. Corticomotor excitability (AURC) for the lesioned M1 showed a significant increase for the AE + tDCS and tDCS conditions compared to the AE condition. There were no differences between the AE + tDCS and tDCS conditions. There were no significant differences for the non-lesioned M1. There were no statistically significant differences in SICI, iSP measures and reaction time between all three conditions.
Conclusions: Our findings suggest that a single session of exercise and tDCS may increase excitability of the lesioned hemisphere, however these effects were specific to the descending corticomotor pathways. There were no alterations in excitability of the inter-hemispheric and intracortical circuits. Moreover, exercise and tDCS did not affect ankle motor control. Our protocol suggests that a combination of exercise and tDCS may be promising for stroke rehabilitation, but further work is required to validate our findings in a larger cohort
