Effects of transcranial direct current stimulation in combination with motor practice on dexterous grasping and manipulation in healthy older adults

Pranav J Parikh,Kelly J Cole

doi:10.1002/phy2.255

Abstract

Transcranial anodal stimulation (tDCS) over primary motor cortex (M1) improves dexterous manipulation in healthy older adults. However, the beneficial effects of anodal tDCS in combination with motor practice on natural and clinically relevant functional manual tasks, and the associated changes in the digit contact forces are not known. To this end, we studied the effects of 20 min of tDCS applied over M1 for the dominant hand combined with motor practice (MP) in a sham‐controlled crossover study. We monitored the forces applied to an object that healthy elderly individuals grasped and manipulated, and their performances on the Grooved Pegboard Test and the Key‐slot task. Practice improved performance on the Pegboard test, and anodal tDCS + MP improved retention of this performance gain when tested 35 min later, whereas similar performance gains degraded in the sham group after 35 min. Interestingly, grip force variability on an isometric precision grip task performed with visual feedback of precision force increased following anodal tDCS + MP, but not sham tDCS + MP. This finding suggests that anodal tDCS over M1 might alter the descending drive to spinal motor neurons involved in the performance of isometric precision grip task under visual feedback leading to increased fluctuations in the grip force exerted on the object. Our results demonstrate that anodal stimulation in combination with motor practice helps older adults to retain their improved performance on a functionally relevant manual task in healthy older adults.

Highlights

After the seventh decade of life, healthy adults experience difficulty in performing dexterous manual tasks such as preparing meals, tying shoelaces, inserting key in its hole, buttoning-unbuttoning clothing (Desrosiers et al 1999; Smith et al 1999)
We investigated the effects of anodal stimulation of the scalp over the region of primary motor cortex (M1) representing the contralateral hand in combination with motor practice in healthy older adults on: (1) performance on functionally relevant Grooved Pegboard test; (2) the completion time during another object manipulation task, the ‘key-slot’ task; (3) the fluctuations in forces applied to an object with a precision grip during a ‘key-slot’ task; and (4) the moment-to-moment force variability during an isometric precision grip task
Post hoc analysis showed that following sham transcranial direct current stimulation (tDCS) + motor practice (MP), but not following anodal tDCS + MP, subjects were significantly slower in completing the Pegboard test 35 min later

Summary

Introduction

After the seventh decade of life, healthy adults experience difficulty in performing dexterous manual tasks such as preparing meals, tying shoelaces, inserting key in its hole, buttoning-unbuttoning clothing (Desrosiers et al 1999; Smith et al 1999). Several intervention techniques such as practice, strength training, peripheral, and cortical stimulation, to mention a few, have been proposed to either improve fine manual performance in older adults or retard its deterioration. Anodal tDCS in combination with motor practice facilitated acquisition and retention of learning on a complex finger-tapping task in older adults (Zimerman et al 2013). This raises an important question whether anodal tDCS when combined with motor practice can improve motor performance on natural and functionally meaningful object manipulation tasks in older adults

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Conclusion