Motor Imagery Affects both Cortical and Spinal Circuitry: A Transcranial and Transspinal Magnetic Stimulation Study

Motor imagery (MI), the mental rehearsal of movement without physical execution, is a key technique in brain-computer interfaces (BCIs) for voluntarily eliciting cortical modulations. Beyond cortical effects, MI could also modulate spinal cord processing, which offers additional potential for neurorehabilitation in conditions like spinal cord injury (SCI) and stroke, where BCIs are used for therapy. To investigate the interactions of MI with both the cortex and the spinal cord, we employed both transcranial magnetic stimulation (TMS) and trans-spinal magnetic stimulation (TSMS). With proper coil orientation, TSMS elicited short- and long-latency motor evoked potentials (MEPs) in forearm muscles and lateralized evoked potentials in the cortex. MI modulated both TMS-induced and TSMS-induced cortical responses and MEPs. This demonstration of MI affecting both cortical and spinal circuitry underscores its potential as a powerful strategy for BCI-driven neurorehabilitation, including pairing MI with magnetic stimulation.