Induction Of Long-term Plasticity In Human Swallowing Motor Cortex Following Repetitive Cortical Stimulation

OBJECTIVE The excitability of corticobulbar projections to swallowing musculature undergoes remarkable long-term increases after short periods of pharyngeal stimulation. The aim of this study was to investigate the excitability of swallowing motor cortex following repetitive transcranial magnetic stimulation (rTMS). METHODS Twelve healthy subjects were given 100 rTMS pulses over motor cortex at frequencies of 1, 5 and 10 Hz at an intensity of 80% threshold for corticobulbar activation. The excitability of the corticobulbar projection was assessed before and after rTMS and compared both to sham stimulation and to the corticospinal projection. RESULTS Stimulation at 5 Hz, but not 1 Hz, 10 Hz or sham stimulation increased the excitability of the corticobulbar projection to the pharynx, reaching a peak 60 min after rTMS (Delta increase: 65%, P=0.016). Excitability in the projection from the opposite hemisphere also increased, suggesting the presence of inter-hemispheric interactions, whereas excitability in the projection to thenar muscles was unchanged. CONCLUSIONS Corticobulbar and corticospinal projections may differ in response to rTMS, implying differences in relative thresholds of inhibitory and excitatory elements in hand versus swallowing cortex. SIGNIFICANCE This might be a useful approach in the motor rehabilitation of dysphagic stroke patients who have damage to sensory projections to the swallowing cortex.