Exp Brain Res (2002) 145:309–315 DOI 10.1007/s00221-002-1094-9 RESEARCH ARTICLE Svetlana Khaslavskaia · Michel Ladouceur · Thomas Sinkjaer Increase in tibialis anterior motor cortex excitability following repetitive electrical stimulation of the common peroneal nerve Received: 22 May 2001 / Accepted: 18 February 2002 / Published online: 15 June 2002 # Springer-Verlag 2002 Abstract The purpose of this study was to investigate whether repetitive electrical stimulation of the common peroneal nerve (CPN) is associated with changes in the motor response of the tibialis anterior (TA) muscle elicitedbyfocalmagneticstimulationofthemotorcortex. Motor evoked potentials (MEP) with a stimulation intensity of 125% of the threshold of the relaxed right TA were obtained before, during, and after repetitive electrical stimulation of the CPN (trains of five pulses of 1 ms, at a frequency of 200 Hz, repeated every second with a 30-min duration). The MEP of the TA muscle elicited after repetitive electrical stimulation were in- creased by 104% (range: 18–263%), and the increase was maintained for up to 110 min (range: 15–110 min) after the end of nerve stimulation. This increase in the MEP of the TA muscle was associated with a decrease in the threshold from the stimulation-response curve. Further- more, during that period the early component of the TA stretch reflex as well as the latency of the MEP did not significantly change. To further test the origin of the increased MEP, complementary experiments showed that MEP elicited by transcranial electrical stimulation (TES) were also increased, but to a lesser degree (approximately 50%)thanMEPelicitedbyTMS.Itcanbeconcludedthat short-term nerve repetitive electrical stimulation of the lower extremities in healthy human participants can lead to a long-term increase in the contralateral MEP. As TES is believed to mainly activate the axon and not the soma of the cortical cells, the increased MEP cannot be explained exclusively by changes in the motor cortex cell excitability, but also by changes in subcortical neural structures involved in the excitation of spinal motoneu- rons. The results of this study allow the speculation that it would be possible to use repetitive electrical stimulation in the rehabilitation of patients with lower limb muscle weakness and spasticity. Keywords Transcranial magnetic cortical stimulation · Corticospinal pathway · Input-output relations · Motor evoked potential · Afferent input · Cortical excitability · Cortical plasticity Introduction TheadultCNShasbeenshowntobeplasticdependingon the sensory input (Buonomano and Merzenich 1998), the motor output (Classen et al. 1998), or injury (Cohen et al. 1998). Furthermore, these changes in the motor cortex have been related to the learning of new motor tasks (Karni et al. 1995; Assanuma and Keller 1991). In recent years, it has been shown that MEP elicited by transcranial magnetic stimulation (TMS) can be altered rapidly by changes in the afferent input as elicited by ischemia (Brasil-Neto et al. 1993) as well as by an electrical stimulation of the nerve of the antagonist muscle (Berto- lasi et al. 1998) or the target muscle (Chen et al. 1999). Furthermore, long-term reorganization, as defined by an effectthatoutlaststhestimulation,ofthemotorcortexhas been reported for repetitive electrical stimulation of peripheral nerves for swallowing (Hamdy et al. 1998) and hand (Ridding et al. 2000) muscles. The duration of thisreorganizationhasbeenreportedtobearound30min, but the mechanisms involved in such long-term reorga- nizations are still under investigation (Kaelin-Lang et al. 2000). The purpose of this study was to investigate the effect of a repetitive stimulation of the CPN on the tibialis anterior(TA)musclerepresentationinthemotorcortexof able-bodied participants. The necessity of investigating thelowerlimbspecificallystemsfromtheresultsshowing that the organization of the segmental system as well as motor cortex and corticospinal pathway is somewhat S. Khaslavskaia · M. Ladouceur ( ) ) · T. Sinkjaer CenterforSensory-MotorInteraction,AalborgUniversity,Aalborg, Denmark e-mail: mladouce@arnie.pec.brocku.ca Tel.: +1-905-68855504615 Fax: +1-905-6888364 M. Ladouceur Department of Physical Education, Brock University, 500 Glenridge Ave., St-Catharines, L2S 3A1, Canada