Characterising the central mechanisms of sensory modulation in human swallowing motor cortex.
OBJECTIVE
Pharyngeal stimulation can induce remarkable increases in the excitability of swallowing motor cortex, which is associated with short-term improvements in swallowing behaviour in dysphagic stroke patients. However, the mechanism by which this input induces cortical change remains unclear. Our aims were to explore the stimulus-induced facilitation of the cortico-bulbar projections to swallowing musculature and examine how input from the pharynx interacts with swallowing motor cortex.


METHODS
In 8 healthy subjects, a transcranial magnetic stimulation (TMS) paired-pulse investigation was performed comprising a single conditioning electrical pharyngeal stimulus (pulse width 0.2 ms, 240 V) followed by cortical TMS at inter-stimulus intervals (ISI) of 10-100 ms. Pharyngeal sensory evoked potentials (PSEP) were also measured over the vertex. In 6 subjects whole-brain magnetoencephalography (MEG) was further acquired following pharyngeal stimulation.


RESULTS
TMS evoked pharyngeal motor evoked potentials were facilitated by the pharyngeal stimulus at ISI between 50 and 80 ms (Delta mean increase: 47+/-6%, P < 0.05). This correlated with the peak latency of the P1 component of the PSEP (mean 79.6+/-8.5 ms). MEG confirmed that the equivalent P1 peak activities were localised to caudolateral sensory and motor cortices (BA 4, 1, 2).


CONCLUSIONS
Facilitation of the cortico-bulbar pathway to pharyngeal stimulation relates to coincident afferent input to sensorimotor cortex.


CONCLUSIONS
These findings have mechanistic importance on how pharyngeal stimulation may increase motor excitability and provide guidance on temporal windows for future manipulations of swallowing motor cortex.
Gow
David
D
Department of GI Sciences, University of Manchester, Clinical Sciences Building, Hope Hospital, Eccles Old Road, Salford M6 8HD, UK.
Hobson
Anthony R
AR
Furlong
Paul
P
Hamdy
Shaheen
S
D000328:Adult; D002490:Central Nervous System / Q000502:physiology*; D003679:Deglutition / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D010614:Pharynx / Q000294:innervation / Q000502:physiology; D012018:Reflex / Q000502:physiology; D012677:Sensation / Q000502:physiology