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

Elisabeth Kaminski; Tom Maudrich; Pauline Bassler; Madeleine Ordnung; Arno Villringer; Patrick Ragert

doi:10.3389/fnagi.2022.935781

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

Front Aging Neurosci. 2022 Sep 20:14:935781. doi: 10.3389/fnagi.2022.935781. eCollection 2022.

Authors

Elisabeth Kaminski^{1

2}, Tom Maudrich^{1

2}, Pauline Bassler², Madeleine Ordnung^{2

3}, Arno Villringer^{2

4

5}, Patrick Ragert^{1

2}

Affiliations

¹ Department of Movement Neuroscience, Faculty of Sport Science, Leipzig University, Leipzig, Germany.
² Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
³ Pediatric Epidemiology, Department of Pediatrics, Medical Faculty, Leipzig University, Leipzig, Germany.
⁴ Berlin School of Mind and Brain, Humboldt-Universität zu Berlin, Berlin, Germany.
⁵ Charité-Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.

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 (LH _trained ) - and right-hand (RH _untrained ) performance was tested before and after training and in three recovery measures 15, 30 and 45 min after training. LH _trained performance improved during both a-tDCS and s-tDCS and improvements persisted during recovery measures for at least 45 min. RH _untrained 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.

Keywords: aging; cross-limb transfer; grooved pegboard task; manual dexterity; transcranial direct current stimulation.