10 th Annual Conference of the International FES Society July 2005 – Montreal, Canada Increased cortical excitability following one session of FET Barsi G, Popovic DB, Sinkjær T, Grey MJ Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University mg@smi.auc.dk Abstract The purpose of this study was to investigate if FET produces a greater increase in cortical excitability than either electrical stimulation (ES) or voluntary (VOL) training alone in able-bodied volunteers. Cortical excitability was assessed with transcranial magnetic stimulation (TMS) by constructing a stimulus- response input-output curve with motor evoked responses of the finger flexor muscles. A 20-minute FET session produced an 83% increase in the maximum height of the input- output curve, whereas ES and VOL produced no increase in cortical excitability. These re- sults suggest that the combination of ES and voluntary exercise might lead to better recov- ery than either ES or voluntary exercise alone. Furthermore, FET might enhance motor re- covery following stroke by increasing cortical excitability, thus promoting cortical plasticity. 1. INTRODUCTION The observation of carry-over effects with Functional Electrical Stimulation has led to the development of electrical stimulation (ES) as a therapeutic intervention for the treatment of stroke [1;2]. One treatment, Functional Electri- cal Therapy (FET) combines intensive voluntary exercise with patterned ES of specific muscle groups to mimic the normal activation of able-bodied humans [1-3]. Results from recent clinical studies have shown promise for the use of FET in the acute phase stroke rehabilitation of upper-limb motor func- tion [1,3]. However, the physiological mechanisms that promote this recovery remain unknown. Both aspects of FET, motor training and ES, have independently been shown to pro- duce cortical reorganisation [e.g. 4;5]. The combination of ES and voluntary motor training (VOL) also produces changes in cortical excit- ability in the tibialis anterior [6-8]. This suggests that one of the primary benefits of FET might be that it promotes functional motor recovery by strengthening corticospinal cir- cuitry. The apparent carry-over effects of FES suggest that upper-limb FET (i.e. voluntary exercise supplemented by peripheral electrical stimula- tion) might also induce increase in cortical excitability. The objective of the present study was to investigate if a single session of FET for finger flexion produces greater changes in cor- tical excitability than either voluntary exercise or peripheral ES alone. 2. METHODS Eight subjects with no known history of neuro- muscular disorder volunteered to participate in this study. All of the experiments were con- ducted in accordance with the Declaration of Helsinki. The experimental protocol was ap- proved by the local ethical committee and all subjects gave their written informed consent prior to their participation. The setup for upper-limb FET is fully described by Popovic et al. [3]. Clinically, upper-limb FET for grasp function is conducted with a four-channel stimulator programmed to control hand opening and closing (finger flex- ion/extension and thumb abduction/adduction). In this study, we used a reduced version of FET where the stimulation was restricted to finger flexion/extension alone. The excitability of the finger flexor area in the motor cortex was ex- amined after 20 minutes of training. 2.1. Electrical Muscle Stimulation The stimulation was applied using disposable self-adhesive surface electrodes with the cath- odes positioned over the respective motor points of the flexor muscles (Flexor Digitorum Profundus (FDP) and Flexor Digitorum Super- ficialis (FDS)) and the Extensor Digitorum Communis (EDC). A common anode was placed on the lateral surface of the forearm just proximal to the wrist. The electrode positions were carefully selected to ensure that the open- ing and closing movements of the hand were as natural as possible. The stimulation pattern was designed to mimic the activity of fingers that is