F139. Paired associative electroacupuncture and transcranial magnetic stimulation in humans

Abstract

Introduction Conventional paired associative stimulation (PAS) consists of repeated pairing of a single electric stimulus at median nerve followed by a transcranial magnetic stimulation (TMS) pulse on the contralateral primary motor cortex (M1) with a specific inter-stimulus interval. It induces associative long-term potentiation (LTP) or depression (LTD)-like plasticity at M1. Attention has been found with a positive influence on such plasticity. In this study we adopt electroacupuncture (EA) to replace the transcutaneous electric stimulation, supposedly drawing a strong attention and enhancing the PAS effect. Methods Eleven healthy, right-handed subjects (aged 23.9 ± 2.2 years, 4 men) were studied. Two hundred and twenty-five pairs of TMS of the left M1 preceded by right EA at acupoint ‘Neiguan’ (Pericardium 6 or PC6, located 2 decimeters proximal from the wrist wrinkle) were respectively applied with an interstimulus interval of individual N20 latency plus 2 ms (N20 + 2) and minus 5 ms (N20-5) with at least one week interval. The paired stimulation was delivered at a rate of 0.25 Hz. Sham TMS with a sham coil was performed to exclude any possible effects from the repetitive low-frequency EA stimulation. M1 excitability was assessed by motor-evoked potential (MEP) recruitment curve with five TMS intensity levels (80–120% resting motor threshold), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and cerebellar inhibition (CBI) at the abductor pollicis brevis (APB) muscle of the right hand before and after the EA-M1 PAS. In addition, median nerve somatosensory-evoked potentials (SSEP) and H-reflex were measured to monitor somatosensory and spinal excitability, respectively. Results All subjects successfully completed four sessions of the experiment. There was no significant change of the MEP amplitude after the EA-M1 PAS at five TMS intensities. SICI, ICF, CBI, SSEP and H-reflex were also not significantly changed after the EA-M1 PAS intervention (all P > 0.05 by paired t-test). Conclusion Transcutaneous electric stimulation replaced by EA is not feasible to induce long-term plasticity-like effect. Complicated sensory afferents evoked by electroacupuncture might hamper instead of enhancing the spike timing dependent motor plasticity in M1.