Sensorimotor modulation of human cortical swallowing pathways
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 506, Issue 3, pages 857–866, February 1998
How to Cite
Hamdy, S., Aziz, Q., Rothwell, J. C., Hobson, A. and Thompson, D. G. (1998), Sensorimotor modulation of human cortical swallowing pathways. The Journal of Physiology, 506: 857–866. doi: 10.1111/j.1469-7793.1998.857bv.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 7 February 1997; accepted after revision 3 October 1997)
- 1Transcranial magnetic stimulation over motor areas of cerebral cortex in man can activate short latency bilateral cortical projections to the pharynx and oesophagus. In the present paper we investigate the interaction between pathways from each hemisphere and explore how activity in these pathways is modulated by afferent feedback from the face, pharynx and oesophagus.
- 2Comparison of unilateral and bilateral stimulation (using interstimulus intervals (ISIs) of 1, 5 or 10 ms between shocks) showed spatial summation of responses from each hemisphere at an ISI of 1 ms, indicating that cortical efferents project onto a shared population of target neurones. Such summation was not evident at ISIs of 5 or 10 ms. There was little evidence for transcallosal inhibition of responses from each hemisphere, as described for limb muscles.
- 3Single stimuli applied to the vagus nerve in the neck or the supraorbital nerve, which alone produce intermediate (onset 20-30 ms) and long (50-70 ms) latency reflex responses in the pharynx and oesophagus, were used to condition the cortical responses. Compared with rest, responses evoked by cortical stimulation were facilitated when they were timed to coincide with the late part of the reflex. The onset latency was reduced during both parts of the reflex response. No facilitation was observed with subthreshold reflex stimuli.
- 4Single electrical stimuli applied to the pharynx or oesophagus had no effect on the response to cortical stimulation. However, trains of stimuli at frequencies varying from 0.2 to 10 Hz decreased the latency of the cortically evoked responses without consistently influencing their amplitudes. The effect was site specific: pharyngeal stimulation shortened both pharyngeal and oesophageal response latencies, whereas oesophageal stimulation shortened only the oesophageal response latencies.
- 5Cortical swallowing motor pathways from each hemisphere interact and their excitability is modulated in a site-specific manner by sensory input. The latter may produce a mixture of excitation and inhibition at both brainstem and cortical levels.