Corticomotor plasticity and learning of a ballistic thumb training task are diminished in older adults

• Published in: Journal of applied physiology (1985) 2009-12, Vol.107 (6), p.1874-1883
• Main Authors: Rogasch, Nigel C, Dartnall, Tamara J, Cirillo, John, Nordstrom, Michael A, Semmler, John G
• Format: Article
• Language: English
• Subjects: Adolescent; Age Factors; Aged; Aged, 80 and over; Aging - physiology; Analysis of Variance; Biological and medical sciences; Electric Stimulation; Electromyography; Evoked Potentials, Motor - physiology; Exercise; Female; Fingers & toes; Fundamental and applied biological sciences. Psychology; Humans; Kinematics; Male; Middle Aged; Motor ability; Motor Cortex - physiology; Motor Skills - physiology; Movement - physiology; Muscle Contraction - physiology; Muscle, Skeletal - physiology; Neural Inhibition - physiology; Neuronal Plasticity - physiology; Neurons - physiology; Older people; Practice (Psychology); Regression Analysis; Signal Processing, Computer-Assisted; Thumb; Transcranial Magnetic Stimulation; Young Adult; Young adults
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00443.2009

Discipline of Physiology and Research Centre for Human Movement Control, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, Australia Submitted 28 April 2009 ; accepted in final form 8 October 2009 This study examined changes in corticomotor excitability and plasticity after a thumb abduction training task in young and old adults. Electromyographic (EMG) recordings were obtained from right abductor pollicis brevis (APB, target muscle) and abductor digiti minimi (ADM, control muscle) in 14 young (18–24 yr) and 14 old (61–82 yr) adults. The training task consisted of 300 ballistic abductions of the right thumb to maximize peak thumb abduction acceleration (TAAcc). Transcranial magnetic stimulation (TMS) of the left primary motor cortex was used to assess changes in APB and ADM motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) before, immediately after, and 30 min after training. No differences in corticomotor excitability (resting and active TMS thresholds, MEP input-output curves) or SICI were observed in young and old adults before training. Motor training resulted in improvements in peak TAAcc in young (177% improvement, P < 0.001) and old (124%, P = 0.005) subjects, with greater improvements in young subjects ( P = 0.002). Different thumb kinematics were observed during task performance, with increases in APB EMG related to improvements in peak TAAcc in young ( r 2 = 0.46, P = 0.008) but not old ( r 2 = 0.09, P = 0.3) adults. After training, APB MEPs were 50% larger ( P < 0.001 compared with before) in young subjects, with no change after training in old subjects ( P = 0.49), suggesting reduced use-dependent corticomotor plasticity with advancing age. These changes were specific to APB, because no training-related change in MEP amplitude was observed in ADM. No significant association was observed between change in APB MEP and improvement in TAAcc with training in individual young and old subjects. SICI remained unchanged after training in both groups, suggesting that it was not responsible for the diminished use-dependent corticomotor plasticity for this task in older adults. motor cortex; transcranial magnetic stimulation; aging Address for reprint requests and other correspondence: J. G. Semmler, School of Molecular and Biomedical Science, Univ. of Adelaide, Adelaide, South Australia 5005 Australia (e-mail: john.semmler{at}adelaide.edu.au ).