Age bias in changes in finger dexterity based on brain activation and spinal motor nerve excitability induced by motor imagery practice

Elderly adults may have poorer recall ability than young adults and may not fully enjoy the effects of motor imagery. To understand the age bias of the effect of motor imagery on hand dexterity, we evaluated brain activation and spinal motor nerve excitability. Brain activation was evaluated from changes in oxygenated hemoglobin concentration, while spinal motor nerve excitability was evaluated from F-waves in eight young (mean age 21.0 +/- 0.5 years) and eight elderly (mean age 69.5 +/- 2.3 years) subjects of matched sex ratio at rest and during motor imagery. Purdue Pegboard scores were also measured before and after motor imagery, and changes in hand dexterity were assessed. The results showed that motor imagery improved hand dexterity without an age bias, and in a similar trend, spinal motor nerve excitability increased during motor imagery. Functional brain connectivity analysis showed the formation of a working memory network in both groups. However, in the analysis of single brain region activation, the young group, but not the elderly group, showed increased activity in the supplementary motor cortex during motor imagery. In addition, regardless of age-related changes, causal coupling indicated the supplementary motor cortex was associated with the changes of spinal motor nerve excitability. Although the changes in brain activation during motor imagery were influenced by age, motor imagery-induced improvements in hand dexterity are also expected in the elderly. Furthermore, changes in spinal motor nerve excitability may be useful in determining the qualitative aspects of motor imagery.