Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition

Eiichi Naito,Minoru Asada,Tomoyo Morita,Satoshi Hirose,Hideya Okamoto,Nodoka Kimura,Chikako Kamimukai

doi:10.1038/s41598-021-02173-7

Abstract

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a super-aging society. Previous studies suggested that the declined interhemispheric sensorimotor inhibition observed in older adults is associated with their deteriorated hand/finger dexterity. Here, we examined whether bimanual digit exercises, which can train the interhemispheric inhibitory system, improve deteriorated hand/finger dexterity in older adults. Forty-eight healthy, right-handed, older adults (65–78 years old) were divided into two groups, i.e., the bimanual (BM) digit training and right-hand (RH) training groups, and intensive daily training was performed for 2 months. Before and after the training, we evaluated individual right hand/finger dexterity using a peg task, and the individual state of interhemispheric sensorimotor inhibition by analyzing ipsilateral sensorimotor deactivation via functional magnetic resonance imaging when participants experienced a kinesthetic illusory movement of the right-hand without performing any motor tasks. Before training, the degree of reduction/loss of ipsilateral motor-cortical deactivation was associated with dexterity deterioration. After training, the dexterity improved only in the BM group, and the dexterity improvement was correlated with reduction in ipsilateral motor-cortical activity. The capability of the brain to inhibit ipsilateral motor-cortical activity during a simple right-hand sensory-motor task is tightly related to right-hand dexterity in older adults.

Highlights

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a superaging society
After the training, using the peg task, we examined whether the right hand/finger dexterity was improved in the BM group, and whether such behavioral improvement was correlated with the reduction of activity in the M1 ROI during the illusion
The average peg time was significantly longer in older adults than in younger adults (22.13 ± 3.65 s [mean ± standard deviation] vs. 20.05 ± 3.19 s; t[77] = 2.59, P = 0.01, effect size d = 0.61), no significant difference in peg time was observed between the two training groups of older adults (BM, 22.23 ± 3.58 s; RH, 22.04 ± 3.78 s; t[46] = 0.18, P = 0.86; Fig. 2, left panel). This indicated that right-hand dexterity was deteriorated in older adults compared with younger adults, and that the pre-training peg time was highly similar between the two groups of older individuals

Summary

Introduction

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a superaging society. Previous studies suggested that the declined interhemispheric sensorimotor inhibition observed in older adults is associated with their deteriorated hand/finger dexterity. Before and after the training, we evaluated individual right hand/finger dexterity using a peg task, and the individual state of interhemispheric sensorimotor inhibition by analyzing ipsilateral sensorimotor deactivation via functional magnetic resonance imaging when participants experienced a kinesthetic illusory movement of the right-hand without performing any motor tasks. Several studies have reported that reduced transcallosal interhemispheric inhibition from the contralateral to the ipsilateral M 17 and hyperactivation of the ipsilateral primary sensorimotor cortex (SM1) in older adults[8] are associated with deteriorated dexterity of their right hand, as evaluated by peg task performance. We set a region-of-interest (ROI) in this M1 region (M1 ROI; 4-mm radius sphere around the M1 peak)

Methods

Results

Conclusion