Submitted on April 30, 2008
Revised on July 9, 2008
Accepted on August 10, 2008
Phasic voluntary movements reverse the after-effects of subsequent theta-burst stimulation in humans
Ennio Iezzi1, Antonella Conte2, Antonio Suppa, Rocco Agostino1, Loredana Dinapoli1, Alessandra Scontrini1, and Alfredo Berardelli3*
1 University of Rome Sapienza
2 Neuromed Institute? (IRCCS)
3 University of Rome
* To whom correspondence should be addressed. E-mail: alfredo.berardelli{at}uniroma1.it.
Theta-burst stimulation (TBS) is a technique that elicits long-lasting changes in the excitability of human primary motor cortex (M1). Tonic contraction of the target muscle modifies the after-effects of TBS, whereas interactions between phasic muscle contraction and the after-effects of TBS are unknown. In this paper we investigated whether phasic voluntary movements influence TBS-induced changes in M1 excitability. We examined whether a brief sequence of phasic finger movements performed by healthy humans before both intermittent TBS (iTBS) and continuous TBS (cTBS) influences TBS-induced after-effects. Ten healthy subjects underwent iTBS and cTBS. To evaluate the TBS-induced after-effects on M1 excitability single TMS pulses were given over the FDI motor area before (T0) and 5 (T1), 15 (T2) and 30 minutes (T3) after TBS. To find out whether finger movements influenced the TBS-induced after-effects we tested motor evoked potentials (MEPs) size by single TMS pulses at T0, immediately after movements and at T1, T2 and T3. We also measured the kinematic variables mean amplitude and mean peak velocity of the movements. When no phasic voluntary movements preceded TBS iTBS elicited facilitatory and cTBS elicited inhibitory after-effects on MEP size. Conversely, movements performed before TBS elicited significant changes in the direction of the TBS-induced after-effects. iTBS produced inhibitory instead of facilitatory after-effects and cTBS produced facilitatory instead of inhibitory after-effects. Finger movements alone had no effects on MEPs size tested with single-pulse TMS. Peripheral electrical stimulation had no effect on iTBS-induced after-effects. Repeated phasic finger movements interfere with TBS-induced after-effects probably by modulating mechanisms of brain metaplasticity.
