Effects of transcranial direct current stimulation of the left primary motor cortex area on hand grip strength and dexterity in healthy individuals: A double-blind randomized sham-controlled trial

Abstract

Background and objective: Motor function plays a critical role in everyday activities, from basic self-care tasks to complex activities that require precision and dexterity. This study was conducted to investigate the effects of transcranial direct current stimulation (tDCS) on grip strength and hand dexterity in healthy individuals.

Method: We conducted a double-blind randomized clinical trial with two groups of sham and active tDCS. The anode was fixed over the primary motor cortex area M1 on the C3 point. The primary outcome was hand grip strength measured by a dynamometer and the secondary outcomes were hand dexterity and assembly assessed by the Purdue Pegboard test. The tDCS program was administered at rest three and two times for the first and second week for a total of five sessions of 20 min each.

Results: There was no significant improvement in the mean difference in grip strength between the sham (N = 27) and active (N = 27) tDCS groups (1.7 vs. 2.3, Mann-Whitney U test, P = 0.869, d = 0.02). Participants who received active tDCS showed subtle improvements in right-hand dexterity (0.6 vs. 1.3, U test P = 0.017, d = 0.33) and overall manual dexterity (1.4 vs. 3.2, U test P = 0.023, d = 0.31) compared with the sham group. Other comparisons for hand dexterity and assembly (motor coordination and fine skills during the manipulation of small objects) between the two groups were not significant. We did not find any adverse effects of sham or active tDCS.

Conclusion: Our study showed a potential for clinical improvement in hand dexterity after five sessions of tDCS in healthy individuals.

Keywords: Assembly; Dexterity; Grip; Hand; Healthy; Transcranial direct current stimulation.