tDCS over the primary motor cortex contralateral to the trained hand enhances cross-limb transfer in older adults

Abstract

Transferring a unimanual motor skill to the untrained hand, a phenomenon known as cross-limb transfer, was shown to deteriorate as a function of age. While transcranial direct current stimulation (tDCS) ipsilateral to the trained hand facilitated cross-limb transfer in older adults, little is known about the contribution of the contralateral hemisphere to cross-limb transfer. In the present study, we investigated whether tDCS facilitates cross-limb transfer in older adults when applied over the motor cortex (M1) contralateral to the trained hand. Furthermore, the study aimed at investigating short-term recovery of tDCS-associated cross-limb transfer. In a randomized, double-blinded, sham-controlled setting, 30 older adults (67.0 ± 4.6 years, 15 female) performed a short grooved-pegboard training using their left hand, while anodal (a-tDCS) or sham-tDCS (s-tDCS) was applied over right M1 for 20 min. Left (LHtrained) - and right-hand (RHuntrained) performance was tested before and after training and in three recovery measures 15, 30 and 45 min after training. LHtrained performance improved during both a-tDCS and s-tDCS and improvements persisted during recovery measures for at least 45 min. RHuntrained performance improved only following a-tDCS but not after s-tDCS and outlasted the stimulation period for at least 45 min. Together, these data indicate that tDCS over the M1 contralateral to the trained limb is capable of enhancing cross-limb transfer in older adults, thus showing that cross-limb transfer is mediated not only by increased bi-hemispheric activation.

Online stimulation of prefrontal cortex during practice increases motor variability and modulates later cognitive transfer: a randomized, double-blinded & sham-controlled tDCS study

“…Interestingly, consistent with the ‘neural overlap hypothesis’, in the c-tDCS but not in the s-tDCS group we observed a medium-sized positive correlation between DBT performance variability and Wii scores. Such near motor transfer effects have recently been observed by [85], manifested as improved cross-limb transfer from the trained to the untrained hand after anodal tDCS over rM1 in older adults. Similarly, we hypothesize that participants in our study were able to successfully use the movement solutions learned during DBT training onto an untrained balance task which also requires a comparable movement pattern in terms of body’s centre of mass (COM) control and displacement.…”

“…Interestingly, consistent with the 'neural overlap hypothesis', in the c-tDCS but not in the s-tDCS group we observed a medium-sized positive correlation between DBT performance variability and Wii scores. Such near motor transfer effects have recently been observed by [85], manifested as improved cross-limb transfer from the trained to the untrained hand after anodal tDCS over rM1 in older adults.…”

Contralesional Anodal Transcranial Direct Current Stimulation Promotes Intact Corticospinal Tract Axonal Sprouting and Functional Recovery After Traumatic Brain Injury in Mice

“…28 Moreover, anodal AtDCS of apparently unrelated spared CSNs on the unaffected side improved hindlimb skilled motor function; this finding is consistent with the phenomenon of "ipsilesional control" observed in prior studies of central nervous system injuries. 8,46,48 Retrograde and anterograde labeling revealed that AtDCS promoted neural connections on the affected side; this may explain the observed improvement of skilled motor function following stimulation. The role of the mTOR pathway, a critical regulator of neuronal axon regeneration, in repairing central nervous system injuries has been extensively studied.…”

“…45 Another study indicated that AtDCS of the unaffected primary motor cortex (responsible for controlling the dominant hand) can improve motor function in older adults, suggesting that ipsilesional control may serve as a potential mechanism for promoting motor function recovery in patients. 46 Researchers elicited latent potential in the unaffected hemisphere and established a novel sensory feedback pathway for the paralyzed hand by manipulating the peripheral nerve through cervical nerve relocation in a preclinical study on animals. 8 In our previous study, AtDCS also exhibited potential in alleviating neuropathic pain after spinal cord injury in preclinical models.…”