The effect of electrical stimulation on corticospinal excitability is dependent on application duration: a same subject pre-post test design
1 School of Health and Rehabilitation Sciences and the NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
2 The Robinson Institute, School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, South Australia 5005, Australia
3 Rehabilitation Science Research Centre, The University of Melbourne, Melbourne, Victoria 3010, Australia
4 School of Science and Health, University of Western Sydney, Campbelltown, NSW, Australia
Journal of NeuroEngineering and Rehabilitation 2013, 10:51 doi:10.1186/1743-0003-10-51Published: 10 June 2013
In humans, corticospinal excitability is known to increase following motor electrical stimulation (ES) designed to mimic a voluntary contraction. However, whether the effect is equivalent with different application durations and whether similar effects are apparent for short and long applications is unknown. The aim of this study was to investigate whether the duration of peripheral motor ES influenced its effect on corticospinal excitability.
The excitability of the corticomotor pathway to abductor pollicis brevis (APB) was measured in fourteen health subjects using transcranial magnetic stimulation before, immediately after and 10 minutes after three different durations (20-, 40-, 60-min) of motor ES (30Hz, ramped). This intervention was designed to mimic a voluntary contraction in APB. To control for effects of motor ES on the peripheral elements (muscle fibre, membrane, neuromuscular junction), maximum compound muscle actions potentials (M-waves) were also recorded at each time point. Results were analysed using a repeated measures analysis of variance.
Peripheral excitability was reduced following all three motor ES interventions. Conversely, corticospinal excitability was increased immediately following 20- and 40-min applications of motor ES and this increase was maintained at least 20-min following the intervention. A 60-min application of motor ES did not alter corticospinal excitability.
A 20-min application of motor ES that is designed to mimic voluntary muscle contraction is as effective as that applied for 40-min when the aim of the intervention is to increase corticospinal excitability. Longer motor ES durations of 60-min do not influence corticospinal excitability, possibly as a result of homeostatic plasticity mechanisms.