Objective In a previous transcranial magnetic stimulation (TMS) study we demonstrated that suprathreshold mesh-glove (MG) whole-hand stimulation elicits lasting changes in motor cortical excitability. Currently, there is no consensus with regard to the optimal parameters for the induction of sensorimotor cortical plasticity using peripheral electrical stimulation. Thus, in the present study we explore the modulatory effects of MG stimulation at different stimulus intensities and different frequencies in order to identify an optimal stimulation protocol. Methods MG stimulation was performed on 12 healthy subjects in separate sessions at different stimulation levels: sub-sensory at 50Hz, sensory at 50Hz and motor at 2Hz. To verify if stimulation at lower frequencies is less effective, an additional experiment at sensory level with 2Hz was performed. TMS was used to assess motor threshold (MT), motor evoked potentials (MEPs) recruitment curve (RC), short latency intracortical inhibition (SICI) and intracortical facilitation (ICF) to paired-pulse TMS at baseline ( T 0), immediately after ( T 1) and 1h ( T 2) after 30min of MG stimulation. F-wave studies were performed to assess spinal motoneuron excitability. Results MG stimulation at sub-sensory/50Hz and sensory/2Hz level determines no significant cortical excitability changes; at sensory/50Hz level and at motor/2Hz level we found decreased MT, increased MEP RC as well as reduced SICI and increased ICF at T 1 and T 2. Conclusions MG stimulation at sensory/50Hz and motor/2Hz level induces similar long-lasting modulatory effects on motor cortical excitability. Both the strength of the corticospinal projections and the intracortical networks are influenced to the same extend. Significance The study provides further evidence that stimulation intensity and frequency can independently modulate motor cortical plasticity. The selection of optimal stimulation parameters has potentially important implications for the neurorehabilitation of patients after brain damage (e.g. stroke, traumatic brain injury) with hand motor deficits.
