Pharyngeal Motor Evoked Potential Research Articles

Chewing modulates the human cortical swallowing motor pathways

When eating, mastication is always followed by swallowing. The present study assessed the effect of mastication on swallowing-related neural pathways in humans. Twenty healthy volunteers participated and underwent baseline transcranial magnetic stimulation to evaluate cortico-pharyngeal and cortico-hand motor-evoked potentials (MEPs). Next, they performed a chewing task and a swallowing task. Repeated-measures ANOVA revealed that pharyngeal MEPs were significantly higher after the swallowing task than after the chewing task, even though the number of swallows across tasks was matched. This implies that chewing movements suppress swallowing-related activity in the pharyngeal motor circuit.

The Effects of Midline Cerebellar rTMS on Human Pharyngeal Cortical Activity in the Intact Swallowing Motor System

We sought to compare the effects of 10 Hz cerebellar vermis (vs. unilateral hemispheric and sham) repetitive transcranial magnetic stimulation (rTMS) on cortical neuroelectrical activity and thereafter 10 Hz cerebellar vermis (vs. sham) rTMS on swallowing behaviour. Healthy participants (n = 25) were randomly allocated to receive vermis, unilateral hemisphere or sham 10 Hz cerebellar rTMS. Recordings were made using pharyngeal electromyography and manometry catheters, obtaining motor-evoked potentials (MEPs) and pressure recordings. The amplitudes of MEPs elicited using single-pulse TMS delivered to the pharyngeal areas of the motor cortex bilaterally were measured pre- and post-cerebellar stimulation. As in previous studies, abductor policis brevis (APB) MEPs were measured to assess post-rTMS modulation specificity. Swallowing was assessed using a swallowing accuracy task. Measurements were made at baseline and 15-min intervals for an hour post-intervention. Measurements involved TMS being used to elicit 10 MEPs bilaterally over the pharyngeal areas of the motor cortex, over the APB cortical representation adjacent to the pharyngeal area with the lowest resting motor threshold and 5 MEPs bilaterally over pharyngeal areas of the cerebellar hemispheres. Swallowing accuracy was assessed by giving participants 10 attempts to swallow and hit a digital target. Cerebellar vermis rTMS caused significant suppression of cortical pharyngeal MEP amplitudes compared with unilateral rTMS and sham (P = 0.0005, 0.002). APB and cerebellar MEP amplitudes were unaffected as were pharyngeal and APB MEP latencies. Following cerebellar vermis rTMS there was a significant reduction in swallowing accuracy compared with sham (P = 0.001). Our findings demonstrate cerebellar vermis rTMS exerts a suppressive effect on pharyngeal motor cortical activity and swallowing behaviour.

Preconditioning human pharyngeal motor cortex enhances directional metaplasticity induced by repetitive transcranial magnetic stimulation.

Recent studies have proposed therapeutic potential for repetitive transcranial magnetic stimulation (rTMS) in swallowing rehabilitation, yet its outcomes vary across individuals and studies. Such variability may be related to the brain state before stimulation. Metaplasticity is a higher order plasticity which regulates cortical response to plasticity changes. Studies have shown that preconditioning of the hand motor cortex could increase cortical capacity for neuroplastic change and enhance rTMS outcomes. We investigated, for the first time, the directional metaplastic properties in human pharyngeal motor cortex using preconditioned rTMS. We found that preconditioned rTMS with specific time intervals between preconditioning and conditioning rTMS had stronger stimulation effects in both swallowing neurophysiology and behaviour than that without preconditioning. Our results provide evidence for enhanced directional metaplasticity in pharyngeal motor cortex and new insights into its clinical application for dysphagia. Despite growing evidence that repetitive transcranial magnetic stimulation (rTMS) can be used as a treatment for dysphagia, its efficacy varies across individuals. Such variability may relate to the pre-stimulation state of neuronal activation. Previous studies found that preconditioning the hand motor cortex before rTMS could enhance stimulation outcomes through metaplasticity. No studies have investigated such mechanisms in human pharyngeal motor cortex. Therefore, we investigated the preconditioning effects of rTMS on swallowing neurophysiology and behaviour. Healthy adults were recruited for swallowing neurophysiological (n=14) and behavioural (n=14) experiments. They were first given eight different preconditioned (1 and 5Hz) rTMS interventions with varying inter-rTMS intervals. Motor evoked potentials (MEPs) were measured before and for 60min post-rTMS. Based on the changes in pharyngeal MEPs, the optimal preconditioned 1Hz and 5Hz rTMS protocols were then applied as interventions while assessing swallowing performance using a reaction time task. We found that 5Hz rTMS preconditioned with 1Hz rTMS with 30min inter-rTMS interval induced the greatest increase on pharyngeal cortical excitability (F1,13 =21.244; P<0.001). By comparison, 1Hz rTMS preconditioned with 5Hz rTMS with 90min inter-rTMS interval was most optimal for suppressing pharyngeal motor cortex (F1,13 =13.547; P=0.003). Behaviourally, swallowing accuracy was improved after preconditioned 5Hz rTMS (F1,13 =10.109, P=0.007) and reduced after preconditioned 1Hz rTMS (F1,13 =14.108, P=0.009) compared to sham. Thus, two optimal protocols for inducing functional metaplasticity in human pharyngeal motor cortex have been identified. These protocols appear superior to conventional rTMS and may be relevant to future clinical application in neurogenic dysphagia.

Lasting modulation of human cortical swallowing motor pathways following thermal tongue stimulation.

Thermal tactile oropharyngeal stimulation has been clinically used to facilitate swallowing initiation in dysphagic patients. We previously demonstrated that thermal stimulation applied to the oral cavity provokes an immediate excitability in pharyngeal motor cortex. The aim of the current study was to investigate whether thermal stimulation can produce longer lasting effects on the corticopharyngeal neural pathway. Healthy volunteers (n=8/12) underwent baseline pharyngeal motor evoked potential (PMEP) measurements evoked by transcranial magnetic stimulation. In the first experiment, subjects received thermal stimulation alternating 30seconds of 15 and 36°C applied to the tongue surface for either 10minutes, 5minutes, or sham. In the second experiment, one of three intermittent thermal stimulus patterns was delivered: cold (alternating 30seconds of 15 and 36°C), warm (continuous 36°C), or hot (alternating 30seconds of 45 and 36°C) for 10minutes. In both experiments, PMEP were remeasured every 15minutes up to 60minutes following thermal stimulation. Repeated measures ANOVA for each stimulus time in the first experiment showed a significant increased change in PMEP amplitude at 30minutes following only 10-minute stimulation compared with sham (P<.05). In the second experiment, we found that cold stimulation was more effective than the other stimulation (P<.05) at increasing PMEP amplitudes. Ten-minute cold stimulation on the tongue can induce a delayed (30minutes) increase in pharyngeal cortical excitability, providing a clinically useful therapeutic window for its application in dysphagic patients.

The effects of unilateral and bilateral cerebellar rTMS on human pharyngeal motor cortical activity and swallowing behavior

The cerebellum is recognised to bilaterally modulate sensorimotor function and has recently been shown to play a role in swallowing. Unilateral cerebellar repetitive trans-cranial magnetic stimulation (rTMS) excites corticobulbar motor pathways to the pharynx but the effects of bilateral versus unilateral cerebellar rTMS on these pathways are unknown. In this three-part cross-over study, healthy participants (n = 13) were randomly allocated to receive unilateral or bilateral 10 Hz cerebellar rTMS. Participants were intubated with pharyngeal electromyography and/or manometry catheters for motor evoked potentials (MEPs) and pressure recordings. In part 1 of the study, single pulse TMS was used to measure baseline motor cortical pharyngeal MEP (PMEP) and hemispheric cerebellar MEP (CMEP) amplitudes, before cerebellar rTMS was administered. Repeat measures of PMEP amplitude were performed at 15-min intervals for an hour post unilateral and bilateral rTMS. Thereafter, in two further studies, a cortical ‘virtual lesion’ (V/L) was applied prior to cerebellar rTMS with pre and post PMEPs (part 2) and measurements of swallowing accuracy (part 3) using a behavioural task. Compared to baseline, unilateral and bilateral cerebellar rTMS provoked increases in pharyngeal cortical excitation (P = 0.028, 0.0005, respectively). Bilateral rTMS was significantly more effective than unilateral in causing cortical excitation (P = 0.0005) and in reversing the suppressive neurological (P = 0.0005) and behavioural (P = 0.0005) effects of a cortical V/L. Our findings suggest bilateral cerebellar rTMS has greater facilitatory effects on corticobulbar motor pathways to the pharynx than unilateral stimulation with the potential to be a more effective clinical therapy if its effects are reproduced in populations with neurogenic dysphagia.

Cerebellar repetitive transcranial magnetic stimulation restores pharyngeal brain activity and swallowing behaviour after disruption by a cortical virtual lesion.

Key points Despite evidence that the human cerebellum has an important role in swallowing neurophysiology, the effects of cerebellar stimulation on swallowing in the disrupted brain have not been explored.In this study, for the first time, the application of cerebellar neurostimulation is characterized in a human model of disrupted swallowing (using a cortical virtual lesion).It is demonstrated that cerebellar stimulation can reverse the suppressed activity in the cortical swallowing system and restore swallowing function in a challenging behavioural task, suggesting the findings may have important therapeutic implications. Repetitive transcranial magnetic stimulation (rTMS) can alter neuronal activity within the brain with therapeutic potential. Low frequency stimulation to the ‘dominant’ cortical swallowing projection induces a ‘virtual‐lesion’ transiently suppressing cortical excitability and disrupting swallowing behaviour. Here, we compared the ability of ipsi‐lesional, contra‐lesional and sham cerebellar rTMS to reverse the effects of a ‘virtual‐lesion’ in health. Two groups of healthy participants (n = 15/group) were intubated with pharyngeal catheters. Baseline pharyngeal motor evoked potentials (PMEPs) and swallowing performance (reaction task) were measured. Participants received 10 min of 1 Hz rTMS to the pharyngeal motor cortex which elicited the largest PMEPs to suppress cortical activity and disrupt swallowing behaviour. Over six visits, participants were randomized to receive 250 pulses of 10 Hz cerebellar rTMS to the ipsi‐lesional side, contra‐lesional side or sham while assessing PMEP amplitude or swallowing performance for an hour afterwards. Compared to sham, active cerebellar rTMS, whether administered ipsi‐lesionally (P = 0.011) or contra‐lesionally (P = 0.005), reversed the inhibitory effects of the cortical ‘virtual‐lesion’ on PMEPs and swallowing accuracy (ipsi‐lesional, P < 0.001, contra‐lesional, P < 0.001). Cerebellar rTMS was able to reverse the disruptive effects of a ‘virtual lesion’. These findings provide evidence for developing cerebellar rTMS into a treatment for post‐stroke dysphagia.

Cold thermal oral stimulation produces immediate excitability in human pharyngeal motor cortex.

Current strategies of swallowing therapy include facilitation of swallowing initiation by sensory modulation. Although thermal tactile oral stimulation is a common method to treat dysphagic patients to improve swallowing movement, little is known about the possible mechanisms. This study is aimed to investigate whether thermal oral (tongue) stimulation can modulate the cortico-pharyngeal neural motor pathway in humans. Eighteen healthy volunteers participated and were intubated with an intraluminal catheter for recording pharyngeal electromyography. Each participant underwent baseline transcranial magnetic stimulation (TMS) cortico-pharyngeal motor evoked potential (MEP) measurements bilaterally. MEPs were then measured during thermal stimulation over the dorsal tongue, applied using the Peltier device at three different temperatures; 45°C, 37°C, and 15°C, in a pre-ordered manner. Each of the three temperatures was given twice with a 5-min resting time between each trial. Averaged MEP amplitude changes were analyzed using ANOVA and post-hoc t-tests. Two-way repeated measures ANOVA with factors of Temperature×Trial in amplitude of MEP demonstrated a significant effect of Temperature both in the stronger (F2,34 =5.775, P=.007) and weaker (F2,34 =4.771, P=.017) pharyngeal hemispheres. Subsequent post-hoc tests showed the significant increase in pharyngeal MEPs at 15° compared to 37° in both hemispheres (P<.05). Cold oral stimulation was able to induce significant changes in pharyngeal cortical excitability, demonstrating evidence for a sensorimotor interaction between oral and pharyngeal cortical areas.

PTU-140 Exciting the Human Swallowing Motor System by Combination Stimuli: Effects of Pharyngeal Stimulation and Carbonated Liquids

Introduction Previous reports have revealed that excitation of human pharyngeal motor cortex can be induced by pharyngeal electrical stimulation (PES) 1 and swallowing carbonated water (CW). 2 This study is aimed to investigate whether synchronously combining PES with swallowing (of still water, SW or CW) can potentiate this excitation in pharyngeal cortical area and brainstem. Our hypothesis was that combining inputs would potentiate cortico-pharyngeal excitability compared to each alone which would be more advantageous in the rehabilitation of dysphagic patients. For the evaluation of the excitation in pharyngeal cortex or brainstem, Transcranial or transcutaneous Magnetic Stimulation (TMS) was used to stimulate the corticobulbar and craniobulbar neural networks. Methods Fourteen healthy volunteers (4 females, age range 19–35 yrs) participated and were intubated with an intraluminal catheter for delivering PES and recording pharyngeal electromyography. Each participants underwent the baseline corticobulbar, craniobulbar and hand motor evoked potential (MEP) measurements with TMS. Subjects were then randomised to receive one of four 10 minute interventions (PES only, ShamPES+CW, PES+CW and PES+SW). Corticobulbar, craniobulbar and hand MEPs were then re-measured for up to 60 minutes. Data were analysed using ANOVA and post hoc t-tests. Results Two way rmANOVA comparing pharyngeal MEP amplitude changes in the dominant hemisphere for Interventions×Time showed a significant interaction, F(15, 195) =2.826, P Conclusion Of the interventions applied, only PES alone was able to induce sustained changes in pharyngeal cortical excitability that built up over time. By contrast, combination stimuli were less effective in promoting enhanced cortical excitability. Of interest, combination stimuli did produce short-term increases in excitability in brain stem reflexes. Our data suggest that PES alone may be most advantageous in dysphagic patients who have a difficulty in performing voluntary swallows. References 1 Fraser, et al . Neuron 2002; 34 :831–40. 2 Elshukri, et al . J Appl Physiol 2016 ; 15;120:408–15. Disclosure of Interest None Declared

Tu1256 Exploring the Association Between Genetic Polymorphisms and Swallowing Motor Cortex Excitability Induced by Repetitive Transcranial Magnetic Stimulation: Is Response Predicted by Genetic Predisposition?

Introduction Non-invasive brain stimulation such as repetitive Transcranial Magnetic Stimulation (rTMS) is used to manipulate excitability in the swallowing motor cortex. However, the molecular mechanisms controlling this excitability remain unknown. Swallowing neurophysiology and impairments might be in part driven by genes. The aim of this study was to determine whether the variability in excitability after 1 Hz and 5 Hz rTMS within the pharyngeal motor cortex might be affected by putative selected single nucleotide polymorphisms (SNPs). Methods 11 SNPs from 7 genes ( BDNF, COMT, TRKB, APOE, DRD2, GRIN2B and GRIN1 ) were selected a priori to explore possible link between neurophysiological outcomes after rTMS intervention with high (5 Hz) and low (1 Hz) frequencies. A total of 41 healthy young (mean age 25.4 ± 4.6 years) volunteers were investigated. All subjects were assessed for corticobulbar excitability after single-pulse TMS. Repeated measurements of motor evoked potentials (MEPs) from the pharynx were recorded before and for up to one hour after the interventions of 1 Hz and 5 Hz rTMS. Salivary DNA was collected and process post-hoc and SNPs correlated with pharyngeal MEPs and interventions (1 vs. 5 Hz rTMS). Results Non-carriers of the minor G allele from SNP rs6269 from COMT gene are more likely to be non-responders ( P -value =0.026), while those carrying G allele are more likely have inhibitory and excitatory outcomes after delivering 1 Hz and 5 Hz rTMS. Cross-tabulation analysis with chi square indicated there was a significant difference between 5 Hz rTMS outcome and one SNP - DRD2 rs1800497: specifically carriers of minor allele A from this DRD2 gene were more strongly inhibited ( P -value =0.03) while non-carriers were more likely to represent non-responders. Conclusion We now report possible evidence for genetic associations with the neuromuscular control of swallowing influenced by rTMS paradigms. Two SNPs from COMT and DRD2 genes appear to play a role in pharyngeal cortex excitability depending on the stimulation applied. Further research is needed to establish more detailed information which might be used in developing more stratified approach in the field of dysphagia therapy with non-invasive brain stimulation. Disclosure of Interest None Declared

Pharyngeal Motor Evoked Potential Monitoring During Skull Base Surgery Predicts Postoperative Recovery from Swallowing Dysfunction

Monitoring pharyngeal motor evoked potential (PhMEP) with a modified endotracheal tube is useful for predicting postoperative swallowing dysfunction. However, the relationship between intraoperative PhMEP findings and recovery from postoperative swallowing dysfunction has not been clarified. The aim of this study was to determine whether PhMEP monitoring predicts swallowing dysfunction not only immediately after surgery but also in the postoperative recovery period. We analyzed PhMEPs in 36 patients during treatment for skull base tumors. Recovery from postoperative swallowing dysfunction was evaluated when oral intake was started postsurgery and drip or tube feeding was discontinued. The correlation between the final to baseline PhMEP ratio and postoperative recovery times from swallowing dysfunction was examined. The PhMEP ratio significantly correlated with postoperative swallowing function immediately after surgery (P < 0.001). The period before starting oral intake in patients with a PhMEP ratio >50% (mean ± standard deviation [SD], 3.8 ± 4.3 days) was shorter than those with a PhMEP ratio ≤50% (mean ± SD, 14.7 ± 11.8 days; P < 0.01). Drip or tube feeding was removed from patients with a PhMEP ratio >50% significantly earlier (mean ± SD, 13.7 ± 19.2 days) than those with a PhMEP ratio ≤50% (mean ± SD, 38.3 ± 27.3 days; P < 0.05). Both univariate and multivariate analysis showed that only the PhMEP ratio was predictive of early recovery from swallowing dysfunction. PhMEP monitoring allowed us to predict not only immediate swallowing dysfunction but also recovery from the dysfunction in the postsurgery period.

PWE-163 The Excitatory Effects Of Repetitive Cerebellar Brain Stimulation On Human Swallowing Motor Pathways Are Critically Dependent On Stimulus Duration

IntroductionPreviously we have demonstrated frequency-specific effects of cerebellar repetitive transcranial magnetic stimulation (rTMS) in enhancing human cortical swallowing pathways,1 as a prelude to developing therapeutic parameters for post-stroke dysphagia. Here,...

O2-E-60. Usefulness of pharyngeal motor evoked potential monitoring during skull base tumor surgery

The aim of this study was to determine whether monitoring of pharyngeal motor evoked potentials (PhMEPs) elicited by transcranial electrical stimulation during skull base tumor surgery might be useful for predicting postoperative swallowing deterioration. The authors analyzed PhMEPs in 27 patients during 28 surgical procedures for the treatment of skull base tumors. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supra-maximal stimuli. PhMEPs were recorded from the posterior wall of the pharynx through a modified endotracheal tube. Postoperative swallowing function was significantly correlated with the final/baseline PhMEP ratio ( r = −0.55, p 50%. In 16 (80%) of these 20 procedures, the patients showed no changes of swallowing function postoperatively ( p

Novel devices for intraoperative monitoring of glossopharyngeal and vagus nerves during skull base surgery

Background:Swallowing disturbance is among the most burdensome complications suffered by patients with glossopharyngeal and vagus nerve involvement in lesions adjacent the jugular foramen. For monitoring these nerves, we have developed new devices that comprised four contacts adhering to the surface of the cuff of an endotracheal tube, with attachment the posterior pharyngeal wall. To determine whether these devices are useful for monitoring the glossopharyngeal and vagus nerves and predicting postoperative swallowing dysfunction in patients undergoing removal of skull base tumors involving these nerves.Methods:We studied 10 patients. Compound muscle action potentials (CMAPs) were recorded from the posterior pharyngeal wall by stimulating the glossopharyngeal or vagus nerve in order to identify the nerve course, especially in patients showing severe nerve distortion due to the tumor. Pharyngeal motor evoked potential (PhMEP) elicited by transcranial electrical stimulation were recorded in all patients. The correlation between the final to baseline PhMEP ratio and postoperative swallowing function was examined.Results:Responses were obtained in six of the seven patients in whom CMAP monitoring was performed. Deterioration of swallowing function postoperatively was demonstrated in six of seven (86%) patients with intraoperative PhMEP ratios <50%. None of the three patients with intraoperative PhMEP ratios >50% showed deterioration of swallowing function after surgery, although the one patient already had severe swallowing dysfunction requiring preoperative tracheostomy.Conclusions:Our novel devices were useful for monitoring the glossopharyngeal and vagus nerves in patients undergoing removal of skull base tumors involving these nerves.

Pharyngeal motor evoked potentials elicited by transcranial electrical stimulation for intraoperative monitoring during skull base surgery

The purpose of this study was to determine whether monitoring of pharyngeal motor evoked potentials (PhMEPs) elicited by transcranial electrical stimulation during skull base tumor surgery might be useful for predicting postoperative swallowing deterioration. The authors analyzed PhMEPs in 21 patients during 22 surgical procedures for the treatment of skull base tumors. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (220-550 V). Pharyngeal MEPs were recorded from the posterior wall of the pharynx through a modified endotracheal tube. The correlation between the final/baseline PhMEP ratio and postoperative swallowing function was examined. Postoperative swallowing function was significantly (p < 0.05), although not strongly (r = -0.47), correlated with the final/baseline PhMEP ratio. A PhMEP ratio < 50% was recorded during 4 of 22 procedures; in all 4 of these cases, the patients experienced postoperative deterioration of swallowing function. After 18 procedures, the PhMEP ratios remained > 50%; nevertheless, after 4 (22.2%) of these 18 procedures, patients showed deterioration of swallowing function. Intraoperative PhMEP monitoring can be useful for predicting swallowing deterioration following skull base surgery, especially in patients with swallowing disturbances that are mainly due to reduction in the motor functions of the pharyngeal muscles.

Val66Met in Brain-Derived Neurotrophic Factor Affects Stimulus-Induced Plasticity in the Human Pharyngeal Motor Cortex

Polymorphisms in brain-derived neurotrophic factor (BDNF) can affect brain and behavioral responses. However, little is known about the effects of a single nucleotide polymorphism (SNP) in BDNF, at codon 66 (the Val-Met substitution, detected in approximately 33% of the Caucasian population) on stimulation-induced plasticity in the cortico-bulbar system. We examined whether this SNP influenced outcomes of different forms of neurostimulation applied to the pharyngeal motor cortex. Thirty-eight healthy volunteers were assessed for corticobulbar excitability after single-pulse, transcranial magnetic stimulation of induced pharyngeal electromyographic responses, recorded from a swallowed intraluminal catheter. Thereafter, volunteers were conditioned with pharyngeal electrical stimulation, or 2 forms of repetitive (1 and 5 Hz) transcranial magnetic stimulation (rTMS). Repeated measurements of pharyngeal motor-evoked potentials were assessed with transcranial magnetic stimulation for as long as 1 hour after the 3 forms of neurostimulation and correlated with SNPs at codon 66 of BDNF (encoding Val or Met). Pharyngeal electrical stimulation significantly increased the amplitude of motor-evoked potentials in individuals with the SNP that encoded Val66, compared to those that encoded Met66, with a strong GENOTYPE*TIME interaction (F₈,₁₁₂ = 2.4; P = .018). By contrast, there was a significant reduction in latencies of subjects with the SNP that encoded Met66 after 5-Hz rTMS (F₃,₆₀ = 4.9; P = .04). In addition, the expected inhibitory effect of 1-Hz rTMS on amplitude was not observed in subjects with the SNP that encoded Met66 in BDNF (F₇,₁₄₀ = 2.23; P = .035). An SNP in human BDNF at codon 66 affects plasticity of the pharyngeal cortex to different forms of neurostimulation. Genetic analysis might help select specific forms of neurostimulation as therapeutics for patients with disorders such as dysphagic stroke.

Modulation of human cortical swallowing motor pathways after pleasant and aversive taste stimuli

Human swallowing involves the integration of sensorimotor information with complexities such as taste; however, the interaction between the taste of food and its effects on swallowing control remains unknown. We assessed the effects of pleasant (sweet) and aversive (bitter) tastes on human cortical swallowing motor pathway excitability. Healthy adult male volunteers underwent a transcranial magnetic stimulation (TMS) mapping study (n = 9, mean age: 34 yr) to assess corticobulbar excitability before and up to 60 min after 10-min liquid infusions either 1) as swallowing tasks or 2) delivered directly into the stomach. Infusions were composed of sterile water (neutral), 10% glucose (sweet), and 0.5 mM quinine hydrochloride (bitter). The order of delivery was randomized, and each infusion was given on separate days. Pharyngeal motor-evoked potentials (PMEPs) were recorded from an intraluminal catheter as a measure of corticobulbar excitability and compared using repeated-measures and one-way ANOVA. After the swallowing task (water, glucose, or quinine), repeated-measures ANOVA revealed a significant time interaction across tastants (P </= 0.01). One-way ANOVA for each taste showed changes in PMEP amplitudes for both quinine (P </= 0.001) and glucose (P </= 0.009) solutions but not for water (P = 0.1). Subsequent t-tests showed that glucose and quinine reduced PMEPs by 47% (SD 34) and 37% (SD 54), respectively, at 30 min (P </= 0.03). No changes were observed after the infusion of any solution directly into the stomach (P = 0.51). In conclusion, cortical swallowing pathways are similarly modulated by both sweet and bitter tasting stimuli. Changes likely reflect a close interaction between taste and swallowing activity mediated in the central nervous system.