Reduced motor cortex plasticity following inhibitory rTMS in older adults

Abstract

Objective: Ageing is accompanied by diminished practice-dependent plasticity. We investigated the effect of age on another plasticity inducing paradigm, repetitive transcranial magnetic stimulation (rTMS).

Methods: Healthy young (n=15; 25+/-4 years) and old (n=15; 67+/-5 years) adults participated in two experiments. Motor evoked potentials (MEPs) were measured in the target muscle (first dorsal interosseus, FDI) and a remote muscle (abductor digiti minimi) during a set of single stimuli. Subjects then received real or sham inhibitory rTMS (intermittent subthreshold trains of 6Hz stimulation for 10min). MEPs were measured for 30min after rTMS.

Results: In young adults, MEPs in the target FDI muscle were approximately 15% smaller in the real rTMS experiment than in the sham rTMS experiment (P<0.026). In old adults, FDI MEP size did not differ between experiments.

Conclusions: Advancing age is associated with reduced efficacy of inhibitory rTMS.

Significance: This work has important implications for the potential therapeutic use of rTMS in stroke and neurological disease.