Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, C16

Oral Communications

Differences between the effects of three plasticity-inducing protocols on the organisation of the human motor cortex

Rosenkranz, Karin; Rothwell, John C;

1. Institute of Neurology, London, United Kingdom.

Several experimental protocols induce lasting changes in the excitability of motor cortex. Some involve direct cortical stimulation, others activate the somatosensory system and some combine motor and sensory stimulation. The effects usually are measured as changes in amplitude of the motor-evoked potential (MEP) or short-interval intracortical inhibition (SICI) elicited by a single or paired pulses of transcranial magnetic stimulation (TMS). Recent work has also tested sensorimotor organisation within the motor cortex by recording MEPs and SICI during short periods of vibration applied to single intrinsic hand muscles. This sensorimotor organisation is focal: MEPs increase and SICI decreases in the vibrated muscle, whilst the opposite occurs in neighbouring muscles [1]. In six volunteers we compared the after effects of three protocols that led to lasting changes in cortical excitability: (i) paired associative stimulation (PAS) between a TMS pulse and an electrical stimulus to the median nerve; (ii) sensory input produced by semi-continuous muscle vibration of the abductor pollicis brevis (APB); and (iii) motor practice of rapid thumb abduction, on MEPs and SICI at rest and on the sensorimotor organisation. PAS increased MEP amplitudes at rest (143

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