The effects of anodal-tDCS on cross-limb transfer in older adults.
OBJECTIVE
Age-related neurodegeneration may interfere with the ability to respond to cross-limb transfer, whereby bilateral performance improvements accompany unilateral practice. We investigated whether transcranial direct current stimulation (tDCS) would facilitate this phenomena in older adults.


METHODS
12 young and 12 older adults underwent unilateral visuomotor tracking (VT), with anodal or sham-tDCS over the ipsilateral motor cortex. Transcranial magnetic stimulation (TMS) assessed motor evoked potentials (MEPs) and short interval intracortical inhibition (SICI). Performance was quantified through a VT error. Variables were assessed bilaterally at baseline and post-intervention.


RESULTS
The trained limb improved performance, facilitated MEPs and released SICI in both age groups. In the untrained limb, VT improved in young for both sham and anodal-tDCS conditions, but only following anodal-tDCS for the older adults. MEPs increased in all conditions, except the older adult's receiving sham. SICI was released in both tDCS conditions for young and old.


CONCLUSIONS
Following a VT task, older adults still display use-dependent plasticity. Although no significant age-related differences between the outcome measures, older adults exhibited significant cross-limb transfer of performance following anodal-tDCS, which was otherwise absent following motor practice alone.


CONCLUSIONS
These findings provide clinical implications for conditions restricting the use of one limb, such as stroke.
Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia. Electronic address: amgood@deakin.edu.au.
Alicia M
AM
Goodwill
Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia. Electronic address: rmdaly@deakin.edu.au.
Robin M
RM
Daly
Department of Rehabilitation, Nutrition and Sport, La Trobe University, Melbourne, Australia. Electronic address: D.Kidgell@latrobe.edu.au.
Dawson J
DJ
Kidgell
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005121:Extremities / Q000294:innervation*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D050781:Transcranial Magnetic Stimulation
Cortical plasticity; Cross-limb transfer; Intracortical inhibition; Ipsilateral motor cortex; Motor practice; tDCS