Repeated spaced paired-associative stimulation to the parietal-motor pathway maintains corticomotor excitability in older adults.

INTRODUCTION

Cortical paired associative stimulation (cPAS), repeated at spaced intervals and applied to the primary motor cortex (M1) and posterior parietal cortex (PPC), has a dose-dependent effect on corticomotor excitability in young adults. The present study investigated whether aging affects this additive (nonhomeostatic) metaplasticity by performing the same manipulation in a sample of older adults.

METHODS

In the multi-dose cPAS condition, three consecutive sessions of the Hebbian-plasticity-induction cPAS protocol were administered with a 50-minute interval between sessions. In the single-dose control cPAS condition, one session of the Hebbian-plasticity-induction cPAS protocol was followed by two sessions of a control non-Hebbian cPAS protocol. We measured motor-evoked potentials (MEPs) before and after each cPAS session.

RESULTS

Compared to a single dose of cPAS, the multi-dose cPAS protocol prevented the reduction in MEP amplitude, resulting in relatively greater corticomotor excitability following the Hebbian procedures. We did not find evidence for an increase in MEP amplitude after the repeated, spaced Hebbian-plasticity-induction cPAS protocol from baseline levels, suggesting reduced neuroplasticity in older adults compared to young adults.

CONCLUSION

Repeated spaced paired-associative stimulation to the parietal-motor pathway maintains corticomotor excitability in older adults.

SIGNIFICANCE

These findings provide insight into age-related differences in neuroplastic capacity in healthy humans.