Introduction Animal studies1 have suggested that the cerebellum plays an important role in the control of swallowing. Moreover human brain imaging studies have reported the activation of the cerebellum in the process of swallowing.2 In this study, we probed the interaction between cerebellum and pharyngeal motor cortical activity with transcranial magnetic stimulation (TMS) to determine if the cerebellum can be excited to induce pharyngeal activity, and also to elucidate if stimulation of the cerebellum can modulate cortical swallowing circuitry in the motor system.
Methods Healthy volunteers (n=16, 8 males, mean age=32) underwent TMS measurements of pharyngeal EMG recorded from a swallowed intra luminal catheter to assess cortical and cerebellar excitability. Subjects then underwent a paired pulse paradigm where active or sham TMS conditioning pulses over the cerebellum were followed by suprathreshold TMS over the cortical pharyngeal area. Paired pulses were delivered at interstimulus intervals (ISIs) of 3, 5, 9, 20, 50, 100 and 200 ms allocated randomly, and the cortical responses were then assessed (compared to baseline and sham) for change in amplitude using T-tests.
Results Stimulation of the cerebellum over the midline or either hemisphere evoked distinct EMG responses in the pharynx. There was a trend towards cerebellar hemispheric stimulation eliciting greater pharyngeal responses (mean amplitude 55.5±6.9 mV) than cerebellar midline stimulation (42.8±5.9 mV); p=0.08. Following active preconditioning cerebellar stimulation, the cortically evoked responses were facilitated with maximal effects at ISIs of 50–200 ms (p< 0.05); in Abstract 019 figure, an effect was not seen with sham preconditioning.
Conclusion This novel study demonstrates that cerebellar stimulation can evoke direct motor responses within the pharynx, and when excited with TMS, can modulate cortical swallowing motor pathways. These findings are in keeping with the animal literature suggesting a facilitatory role for the cerebellum in regulating swallowing and raises the possibility that excitatory neurostimulation of the cerebellum may be therapeutically useful in promoting recovery of dysphagia after brain damage.
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