Cranial nerve modulation of human cortical swallowing motor pathways

The Impact of Periventricular Leukoaraiosis in Post-stroke Oropharyngeal Dysphagia: A Swallowing Biomechanics and MRI-Based Study

Oropharyngeal dysphagia is a highly prevalent post-stroke complication commonly associated with topographically specific gray-matter damage. In contrast, the role of damage to the extensive white matter brain network (leukoaraiosis) in post-stroke oropharyngeal dysphagia has not yet been clarified. We aim to assess the role of leukoaraiosis in post-stroke oropharyngeal dysphagia. We designed a cross-sectional study and retrospectively collected from our database patients with dysphagia affected by a recent stroke and on whom both a brain 1.5 T-MRI and a videofluoroscopy had been performed. Leukoaraiosis was assessed in brainstem and in cerebral regions (periventricular or deep) with Fazekas scale. Penetration-Aspiration-Scale and time to laryngeal vestibule closure and to upper esophageal sphincter opening were analyzed. Study population (n = 121; 57% men, 75.5 ± 9.4y) presented mostly supratentorial ischemic PACI-type strokes. Of the patients, 86% had unsafe swallows (PAS = 3.97 ± 2.04); 94.2% had cerebral leukoaraiosis (Fazekas = 3.36 ± 1.7) and 42.1% had brainstem-leukoaraiosis, hypertension being the main risk factor. We found both significant positive associations between degree of periventricular-leukoaraiosis and total-leukoaraiosis and presence of risk of aspirations (p = 0.016 and p = 0.023, respectively); and a correlation between periventricular-leukoaraiosis and PAS scale severity (r = 0.179, p = 0.049). No correlations/associations were found between stroke volume and dysphagia in this study. Our study supports a role for leukoaraiosis in the pathophysiology of dysphagia. Stroke is associated with chronic short-connection/circuit injury and damage to periventricular white matter long connections is a relevant neuro-pathophysiological mechanism contributing to impaired safety of swallow in post-stroke oropharyngeal dysphagia patients.

The Role of White Matter in the Neural Control of Swallowing: A Systematic Review

Background: Swallowing disorders (dysphagia) can negatively impact quality of life and health. For clinicians and researchers seeking to improve outcomes for patients with dysphagia, understanding the neural control of swallowing is critical. The role of gray matter in swallowing control has been extensively documented, but knowledge is limited regarding the contributions of white matter. Our aim was to identify, evaluate, and summarize the populations, methods, and results of published articles describing the role of white matter in neural control of swallowing.

Methods: We completed a systematic review with a multi-engine search following PRISMA-P 2015 standards. Two authors screened articles and completed blind full-text review and quality assessments using an adapted U.S. National Institute of Health's Quality Assessment. The senior author resolved any disagreements. Qualitative synthesis of evidence was completed.

Results: The search yielded 105 non-duplicate articles, twenty-two of which met inclusion criteria. Twenty were rated as Good (5/22; 23%) or Fair (15/22; 68%) quality. Stroke was the most represented diagnosis (n = 20; 91%). All studies were observational, and half were retrospective cohort design. The majority of studies (13/22; 59%) quantified white matter damage with lesion-based methods, whereas 7/22 (32%) described intrinsic characteristics of white matter using methods like fractional anisotropy. Fifteen studies (68%) used instrumental methods for swallowing evaluations. White matter areas commonly implicated in swallowing control included the pyramidal tract, internal capsule, corona radiata, superior longitudinal fasciculus, external capsule, and corpus callosum. Additional noteworthy themes included: severity of white matter damage is related to dysphagia severity; bilateral white matter lesions appear particularly disruptive to swallowing; and white matter adaptation can facilitate dysphagia recovery. Gaps in the literature included limited sample size and populations, lack of in-depth evaluations, and issues with research design.

Conclusion: Although traditionally understudied, there is sufficient evidence to conclude that white matter is critical in the neural control of swallowing. The reviewed studies indicated that white matter damage can be directly tied to swallowing deficits, and several white matter structures were implicated across studies. Further well-designed interdisciplinary research is needed to understand white matter's role in neural control of normal swallowing and in dysphagia recovery and rehabilitation.

Effect of Transcutaneous Electrical Stimulation in Chronic Poststroke Patients with Oropharyngeal Dysphagia: 1-Year Results of a Randomized Controlled Trial

Background. Chronic poststroke oropharyngeal dysphagia (CPSOD) is associated with impaired oropharyngeal sensory/motor function. We aimed to assess effect of sensory (SES) and motor (NMES) transcutaneous electrical stimulation (TES) on safety of swallow and clinical outcomes in patients with CPSOD in a one-year follow-up randomized controlled trial. Methods. Ninety patients (74.1 ± 11.5 y, modified Rankin score 2.6 ± 1.7) with CPSOD and impaired safety of swallow were randomized to (a) compensatory treatment (CT), (b) CT + SES, and (c) CT + NMES. Patients were treated with up to two cycles (6 months apart) of 15 × 1 hour TES sessions over two weeks and followed up with 4-5 clinical and videofluoroscopic assessments during one year. Key results. Baseline penetration-aspiration scale (PAS) was 4.61 ± 1.75, delayed time to laryngeal vestibule closure (LVC) 396.4 ± 108.7 ms, and impaired efficacy signs 94.25%. Swallowing parameters significantly improved between baseline and 1-year follow-up in SES and NMES groups for prevalence of patients with a safe swallow (P < .001), mean PAS (P < .001), time to LVC (P < .01), and need for thickening agents (P < .001). Patients in the CT presented a less intense improvement of signs of impaired safety of swallow without significant changes in time to LVC. No differences between groups were observed for 1-year mortality (6.1%), respiratory infections (9.6%), nutritional and functional status, QoL, and hospital readmission rates (27.6%). No significant adverse events related to TES were observed. Conclusions and inferences. Transcutaneous electrical stimulation is a safe and effective therapy for older patients with CPSOD. After 1-year follow-up, TES greatly improved the safety of swallow and reduced the need for fluid thickening in these patients.

Pre- and Post-Surgical Dysphagia in Adults with Tumors of the Posterior Fossa: A Prospective Blinded Study

BACKGROUND

While swallowing disorders are frequent sequela following posterior fossa tumor (PFT) surgery in children, data on dysphagia frequency, severity, and outcome in adults are lacking. The aim of this study was to investigate dysphagia before and after surgical removal of PFT. Additionally, we tried to identify clinical predictors for postsurgical swallowing disorders. Furthermore, this study explored the three-month outcome of dysphagic patients.

METHODS

In a cohort of patients undergoing PFT surgery, dysphagia was prospectively assessed pre- and postoperatively using fiberoptic endoscopic evaluation of swallowing. Patients with severe dysphagia at discharge were re-evaluated after three months. Additionally, clinical and imaging data were collected to identify predictors for post-surgical dysphagia.

RESULTS

We included 26 patients of whom 15 had pre-operative swallowing disorders. After surgery, worsening of pre-existing dysphagia could be noticed in 7 patients whereas improvement was observed in 2 and full recovery in 3 subjects. New-onset dysphagia after surgery occurred in a minority of 3 cases. Postoperatively, 47% of dysphagic patients required nasogastric tube feeding. Re-evaluation after three months of follow-up revealed that all dysphagic patients had returned to full oral intake.

CONCLUSION

Dysphagia is a frequent finding in patients with PFT already before surgery. Surgical intervention can infer a deterioration of impaired swallowing function placing affected patients at temporary risk for aspiration. In contrast, surgery can also accomplish beneficial results resulting in both improvement and full recovery. Overall, our findings show the need of early dysphagia assessment to define the safest feeding route for the patient.

Targeting Chemosensory Ion Channels in Peripheral Swallowing-Related Regions for the Management of Oropharyngeal Dysphagia

Oropharyngeal dysphagia, or difficulty in swallowing, is a major health problem that can lead to serious complications, such as pulmonary aspiration, malnutrition, dehydration, and pneumonia. The current clinical management of oropharyngeal dysphagia mainly focuses on compensatory strategies and swallowing exercises/maneuvers; however, studies have suggested their limited effectiveness for recovering swallowing physiology and for promoting neuroplasticity in swallowing-related neuronal networks. Several new and innovative strategies based on neurostimulation in peripheral and cortical swallowing-related regions have been investigated, and appear promising for the management of oropharyngeal dysphagia. The peripheral chemical neurostimulation strategy is one of the innovative strategies, and targets chemosensory ion channels expressed in peripheral swallowing-related regions. A considerable number of animal and human studies, including randomized clinical trials in patients with oropharyngeal dysphagia, have reported improvements in the efficacy, safety, and physiology of swallowing using this strategy. There is also evidence that neuroplasticity is promoted in swallowing-related neuronal networks with this strategy. The targeting of chemosensory ion channels in peripheral swallowing-related regions may therefore be a promising pharmacological treatment strategy for the management of oropharyngeal dysphagia. In this review, we focus on this strategy, including its possible neurophysiological and molecular mechanisms.

Efficacy of Botulinum Toxin for Treating Sialorrhea in Neuromuscular Conditions

Background: Drooling related to bulbar weakness and dysfunction is a common concern in patients with neuromuscular disease. While there are numerous medications to manage sialorrhea, they are often limited by side effects and lack of efficacy. Botulinum toxin has shown to benefit ALS patients in a few studies, but there is scant data on the benefit in other neuromuscular conditions. Objective: To assess the effectiveness of Botulinum toxin in reducing sialorrhea in patients with various neuromuscular disease. Design/Methods: 25 patients (19M, 6F; 54.36 ± 17.09 yr) with documented neuromuscular illness and concern for drooling was followed for 6 weeks after Botulinum toxin injection. These patients had one of the following diagnoses: Duchenne muscular dystrophy (3), myotonic dystrophy (3), oculopharyngeal muscular dystrophy (1), inclusion body myositis (2), primary lateral sclerosis (1), amyotrophic lateral sclerosis (9), spinal muscular atrophy type 2 and 3 (2), spinal-bulbar muscular atrophy (2), and Becker's muscular dystrophy (2). A subjective drooling scale (1: markedly worse, 5: markedly better) and drooling thickness score (0=normal, 100=thick) was calculated on these patients prior to the injection and 4 and 6 weeks after the injection. Botulinum toxin 20-30 units were injected into bilateral parotid gland (70% of the dose) and submandibular gland (30% of the dose). Results: The drooling thickness score at before the injection was 75.2 ± 10.46. At 4 and 6 weeks, average scores reduced to 47.2 ± 6.14 and 18.8 ± 5.26, respectively (p < 0.05). The average pre injection perception about drooling was 3.0 (p < 0.05). The average change in perception was +0.84 and +1.28 at 4 and 6 weeks, respectively, (p < 0.05) implying significant improvement. There were no reported adverse effects. Conclusion: This study provides preliminary evidence for the use of botulinum toxin for refractory sialorrhea for a variety of neuromuscular conditions.

Effect of thalamic deep brain stimulation on swallowing in patients with essential tremor

Objective

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) is a mainstay treatment for severe and drug‐refractory essential tremor (ET). Although stimulation‐induced dysarthria has been extensively described, possible impairment of swallowing has not been systematically investigated yet.

Methods

Twelve patients with ET and bilateral VIM‐DBS with self‐reported dysphagia after VIM‐DBS were included. Swallowing function was assessed clinically and using by flexible endoscopic evaluation of swallowing in the stim‐ON and in the stim‐OFF condition. Presence, severity, and improvement of dysphagia were recorded.

Results

During stim‐ON, the presence of dysphagia could be objectified in all patients, 42% showing mild, 42% moderate, and 16 % severe dysphagia. During stim‐OFF, all patients experienced a statistically significant improvement of swallowing function.

Interpretation

VIM‐DBS may have an impact on swallowing physiology in ET‐patients. Further studies to elucidate the prevalence and underlying pathophysiological mechanisms are warranted.

Therapy of Dysphagia by Prolonged Pharyngeal Electrical Stimulation (Phagenyx) in a Patient with Brainstem Infarction

Dysphagia after stroke impacts quality of life and is a risk factor for respiratory infections. Patients frequently require prophylactic measures including nasogastric tube or percutaneous endoscopic gastrostomy. Until recently, therapy for dysphagia was limited to training with a speech and language specialist. Intraluminal pharyngeal electrical stimulation (PES) is a new technique that stimulates the pharyngeal sensory afferents to the higher swallowing center in cortex. The clinical trials published to date involved stimulation for 10 minutes over three days. We present a case of brainstem infarction with severe dysphagia in a 53-year-old woman with preserved cognitive functions. For airway protection, she had a surgical tracheotomy. The initial swallowing training achieved slight improvements, but stagnated after three months so PES was tried. Under good PES tube tolerance, a prolonged and repeated stimulation protocol was administered, with the main purpose of relieving her of the tracheal tube. Although the swallowing improved, she stayed tube-dependent with minimal attempts with puréed food during therapy, and could not be decannulated. Further studies are required to assess the value of this promising approach for the treatment of dysphagia.

Acute and subacute effects of oropharyngeal sensory stimulation with TRPV1 agonists in older patients with oropharyngeal dysphagia: a biomechanical and neurophysiological randomized pilot study

BACKGROUND

Older people with oropharyngeal dysphagia (OD) present a decline in pharyngeal sensory function. The aim of this proof-of-concept study was to assess the biomechanical and neurophysiological effects of acute and subacute oropharyngeal sensory stimulation with transient receptor potential vanilloid 1 (TRPV1) agonists (capsaicinoids) in older patients with OD.

METHODS

We studied the effect of a single dose versus multiple doses (2 weeks) of oral capsaicin treatment (10^-5 M) or placebo in 28 older patients with OD (81.2 ± 4.6 years) using videofluoroscopy (penetration-aspiration scale [PAS], timing of swallow response) and electroencephalography (EEG) (latency and amplitude of pharyngeal event-related potential [ERP]).

RESULTS

Acute stimulation by capsaicinoids 10^-5 M did not improve swallow function and did not produce significant changes in pharyngeal ERP. In contrast, after 10 days of treatment, patients presented a clinically relevant and statistically significant reduction in the laryngeal vestibule closure (LVC) time (22.5%, p = 0.042), and in the PAS (24.2%, p = 0.038), compared with the placebo group. EEG results showed a reduction in the latency of the N1 peak (28.6%, p = 0.007) and an increase of the amplitude of the P1-N2 (59.4%, p = 0.038) and the N2-P2 (43.6%, p = 0.050) peaks. We observed a strong and significant correlation between the reduction in the latency of the N1 peak and change in LVC time after subacute treatment (r = 0.750, p = 0.003).

CONCLUSIONS

After 2 weeks of treatment, oropharyngeal sensory stimulation with capsaicinoids induced cortical changes that were correlated with improvements in swallowing biomechanics in older patients with OD. These results further show that sensory stimulation by TRPV1 agonists can become a useful pharmacological treatment for older patients with OD.

The Effectiveness of Botulinum Toxin Type A Injections in the Management of Sialorrhea

OBJECTIVE

The aim of this study was to evaluate the effect of Botulinum toxin type A by injecting in the submandibular and parotid glands on the frequency and severity of sialorrhea.

METHODS

Pediatric patients who were referred to our department with sialorrhea were evaluated using their parents' frequency and severity scores of sialorrhea with visual analog scales before and after 3 months of botulinum toxin type A injections. Bilateral submandibular and parotid glands were injected with Botulinum toxin type A.

RESULTS

Twenty-seven pediatric patients who were referred to our department with a complaint of sialorrhea were included in this study. Seventeen patients were female and 10 were male. Severe sialorrhea with cerebral palsy was present in all the patients. There were no complications after the procedure.

CONCLUSION

Botulinum toxin A injected in the major salivary glands in pediatric patients with neurological disorders is a safe and effective method.

Influence of attention and bolus volume on brain organization during swallowing

It has been shown that swallowing involves certain attentional and cognitive resources which, when disrupted can influence swallowing function with in dysphagic patient. However, there are still open questions regarding the influence of attention and cognitive demands on brain activity during swallowing. In order to understand how brain regions responsible for attention influence brain activity during swallowing, we compared brain organization during no-distraction swallowing and swallowing with distraction. Fifteen healthy male adults participated in the data collection process. Participants performed ten 1 ml, ten 5 ml, and ten 10 ml water swallows under both no-distraction conditions and during distraction while EEG signals were recorded. After standard pre-processing of the EEG signals, brain networks were formed using the time-frequency based synchrony measure. The brain networks formed were then compared between the two sets of conditions. Results showed that there are differences in the Delta, Theta, Alpha, Beta, and Gamma frequency bands between no-distraction swallowing and swallowing with distraction. Differences in the Delta and Theta frequency bands can be attributed to changes in subliminal processes, while changes in the Alpha and Beta frequency bands are directly associated with the various levels of attention and cognitive demands during swallowing process, and changes in the Gamma frequency band are due to changes in motor activity. Furthermore, we showed that variations in bolus volume influenced the swallowing brain networks in the Delta, Theta, Alpha, Beta, and Gamma frequency bands. Changes in the Delta, Theta, and Alpha frequency bands are due to sensory perturbations evoked by the various bolus volumes. Changes in the Beta frequency band are due to reallocation of cognitive demands, while changes in the Gamma frequency band are due to changes in motor activity produced by variations in bolus volume. These findings could potentially lead to the development of better understanding of the nature of dysphagia and various rehabilitation strategies for patients with neurogenic dysphagia who have altered attention or impaired cognitive functions.

Localization and expression of TRPV1 and TRPA1 in the human oropharynx and larynx

BACKGROUND

Previous studies have found that TRPV1 and TRPA1 receptor agonists improve swallow response in patients with oropharyngeal dysphagia (OD), but little is known about the expression of these receptors in the human oropharynx. The aim of this study was to assess the expression and localization of TRPV1 and TRPA1 in human samples from the oropharynx of healthy patients, to provide the basis for new pharmacological treatments for OD.

METHODS

Samples from oropharyngeal regions innervated by cranial nerves V, IX, and X (tongue, pharynx, and epiglottis) were obtained during ENT surgery and processed either for mRNA (21 patients) or for immunohistochemical assays (seven patients). The expression analysis was performed with RT-qPCR using ACTBh as reference gene. Hemotoxylin and eosin staining was used to study the histology; the immunohistochemical assay used (i) neuron-specific enolase to detect nerve fibers or (ii) fluorescent probes to locate TRPV1 and TRPA1.

RESULTS

TRPV1 was expressed in the three studied regions, with higher levels in CN V region (tongue) than in CN X region (epiglottis; p < 0.05), and was localized at epithelial cells and nociceptive fibers in all studied regions. TRPA1 was also expressed in all studied regions, but was always localized below the basal lamina. No immunoreactivity for TRPA1 was found on epithelial cells.

CONCLUSIONS & INFERENCES

TRPV1 and TRPA1 are widely expressed in the human oropharynx with two distinct patterns. Our study further confirms that TRPV1/A1 receptors are promising therapeutic targets to develop active treatments for OD patients.

Brain and behavioral effects of swallowing carbonated water on the human pharyngeal motor system

Chemical stimulation of the swallowing network with carbonation and citric acid has been investigated, showing potential benefits on swallowing of dysphagic patients. Despite this, the underlying mechanisms for these effects are not fully understood. Here we investigated the effects of 5 ml liquid bolus swallows of carbonated, citric acid, and still water on a swallowing reaction-time tasks paradigm in 16 healthy adults (8 male, mean age 33 ± 3.7 yr, protocol 1). We then investigated the net effects of "sensory bolus interventions" (40 repeated swallows every 15 s) of the three different liquid boluses on corticobulbar excitability, as examined with single-pulse transcranial magnetic stimulation (TMS) in 16 participants (8 female, mean age 33 ± 3.7 yr, protocol 2). The findings showed that a larger number of correctly timed swallows (within a predetermined time window) was accomplished mainly with carbonated liquids (z = -2.04, P = 0.04 vs. still water, protocol 1). Both carbonated and citric acid liquid interventions with 40 swallows increased corticobulbar excitability of the stronger pharyngeal projection, suggesting a similar modulatory pathway for the effects on swallowing. However, carbonation showed superiority (P = 0.04, F = 4.75, 2-way ANOVA), with the changes lasting up to 60 min following the intervention. These results hold significance for future further and in-depth physiological investigations of the differences between different stimuli on swallowing neural network.

An unusual complication of Botox treatment for sialorrhoea

INTRODUCTION

To illustrate the potential side effects and clinical efficacy of Botox injections in treating sialorrhoea.

PRESENTATION OF CASE

A 26-year-old patient with cerebral palsy with dystonia had a long history of severe, distressing sialorrhoea. She was treated with three separate Botox injections into her salivary glands in December 2011, July 2012 and March 2013.

DISCUSSION

Following the Botox injections the patient developed dysphagia, began to expectorate thick mucus and developed a cough; she was treated for a chest injection and during this time her feeding deteriorated. Three injections were given as the patient had an objective and significant reduction in salivation. However, the side effect profile was deemed too great to continue with treatment.

CONCLUSION

Botox is a novel and effective treatment for reducing saliva production. Its clinical efficacy is supported by this case and correlates with the recent literature. Although rare, significant side effects can happen and the case presented illustrates the care needed when administering injections, particularly in a subgroup of patients.

Dysphagia Management in Acute and Sub-acute Stroke

Swallowing dysfunction is common after stroke. More than 50% of the 665 thousand stroke survivors will experience dysphagia acutely of which approximately 80 thousand will experience persistent dysphagia at 6 months. The physiologic impairments that result in post-stroke dysphagia are varied. This review focuses primarily on well-established dysphagia treatments in the context of the physiologic impairments they treat. Traditional dysphagia therapies including volume and texture modifications, strategies such as chin tuck, head tilt, head turn, effortful swallow, supraglottic swallow, super-supraglottic swallow, Mendelsohn maneuver and exercises such as the Shaker exercise and Masako (tongue hold) maneuver are discussed. Other more recent treatment interventions are discussed in the context of the evidence available.

Sialorrhea: anatomy, pathophysiology and treatment with emphasis on the role of botulinum toxins

Sialorrhea or excessive drooling is a major issue in children with cerebral palsy and adults with neurodegenerative disorders. In this review, we describe the clinical features, anatomy and physiology of sialorrhea, as well as a review of the world literature on medical treatment using Yale University’s search engine; including but not limited to Medline and Erasmus. Level of drug efficacy is defined according to the guidelines of American Academy of Neurology. Current medical management is unsatisfactory. Topical agents (scopolamine and tropicamide) and oral agents (glyccopyrolate) combined render a level B evidence (probably effective); however, this treatment is associated with troublesome side effects. Double-blind and placebo-controlled studies of botulinum toxin (BoNT) provide a level A evidence for type B (two class I studies; effective and established) and both overall and individual B level of evidence for OnabotulinumtoxinA (A/Ona) and AbobotulinumtoxinA (A/Abo); these are probably effective. For IncobotulinumtoxinA (A/Inco), the level of evidence is U (insufficient) due to lack of blinded studies. Side effects are uncommon; transient and comparable between the two types of toxin. A clinical note at the end of this review comments on fine clinical points. Administration of BoNTs into salivary glands is currently the most effective way of treating sialorrhea.

Sensory input pathways and mechanisms in swallowing: a review

Over the past 20 years, research on the physiology of swallowing has confirmed that the oropharyngeal swallowing process can be modulated, both volitionally and in response to different sensory stimuli. In this review we identify what is known regarding the sensory pathways and mechanisms that are now thought to influence swallowing motor control and evoke its response. By synthesizing the current state of research evidence and knowledge, we identify continuing gaps in our knowledge of these mechanisms and pose questions for future research.

Tactile thermal oral stimulation increases the cortical representation of swallowing

Background

Dysphagia is a leading complication in stroke patients causing aspiration pneumonia, malnutrition and increased mortality. Current strategies of swallowing therapy involve on the one hand modification of eating behaviour or swallowing technique and on the other hand facilitation of swallowing with the use of pharyngeal sensory stimulation. Thermal tactile oral stimulation (TTOS) is an established method to treat patients with neurogenic dysphagia especially if caused by sensory deficits. Little is known about the possible mechanisms by which this interventional therapy may work. We employed whole-head MEG to study changes in cortical activation during self-paced volitional swallowing in fifteen healthy subjects with and without TTOS. Data were analyzed by means of synthetic aperture magnetometry (SAM) and the group analysis of individual SAM data was performed using a permutation test.

Results

Compared to the normal swallowing task a significantly increased bilateral cortical activation was seen after oropharyngeal stimulation. Analysis of the chronological changes during swallowing suggests facilitation of both the oral and the pharyngeal phase of deglutition.

Conclusion

In the present study functional cortical changes elicited by oral sensory stimulation could be demonstrated. We suggest that these results reflect short-term cortical plasticity of sensory swallowing areas. These findings facilitate our understanding of the role of cortical reorganization in dysphagia treatment and recovery.

Effects of oropharyngeal air-pulse stimulation on swallowing in healthy older adults

While previous research has shown that air-pulse stimulation of the oropharynx facilitates saliva swallowing in young adults, the effects of air pulses in older adults have not been examined. Responses to air-pulse stimulation may differ in young and older adults given age-related changes in sensation, swallowing physiology, and swallow-related brain activation. Therefore, this study sought to determine the effects of oropharyngeal air-pulse stimulation on saliva swallowing rates in 18 healthy older adults. Saliva swallowing rates were monitored across six conditions: baseline without mouthpiece, baseline with mouthpiece in situ, unilateral right oropharyngeal stimulation, unilateral left oropharyngeal stimulation, bilateral oropharyngeal stimulation, and sham stimulation. Results indicated that bilateral oropharyngeal air-pulse stimulation was associated with a statistically significant increase in mean saliva swallowing rate compared to baseline without mouthpiece, baseline with mouthpiece in situ, and sham stimulation. In previous studies, young adults reported an irrepressible urge to swallow in response to oropharyngeal air-pulse delivery, but the older adults in the current study did not perceive the air-pulse stimulation as being associated with swallowing or other behaviors. These findings indicate that oropharyngeal air-pulse stimulation facilitates the elicitation of saliva swallowing in older adults.

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.

Changes in pharyngeal corticobulbar excitability and swallowing behavior after oral stimulation

Faucial pillar (FP) stimulation is commonly used in swallowing rehabilitation, yet its physiological basis remains uncertain. We investigated the effects of intraoral FP stimulation on human corticobulbar excitability and swallowing behavior, to explore the possibility of a central mechanism for functional change. In 10 healthy subjects, corticobulbar projections to pharynx were investigated with transcranial magnetic stimulation, via intraluminal electrodes, before and up to 1 h after 10 min of electrical FP stimulation with three frequencies (0.2, 1, and 5 Hz) or sham and peripheral (median nerve) stimulation. In a second study, swallowing behavior was assessed with videofluoroscopy before and after FP stimulation. FP stimulation at 5 Hz inhibited the corticobulbar projection (-14 +/- 6%, P < 0.02) and lengthened swallow response time (+114 +/- 24%, P = 0.02). By comparison, FP stimulation at 0.2 Hz facilitated this projection (+60 +/- 28%, P < 0.04), without enhancing swallowing behavior. Neither 1-Hz, sham, nor median nerve stimulation altered excitability. Thus changes in corticobulbar excitability to FP stimulation are frequency dependent with implications for the treatment for neurogenic swallowing dysfunction.

Differential changes in human pharyngoesophageal motor excitability induced by swallowing, pharyngeal stimulation, and anesthesia

We investigated the effects of water swallowing, pharyngeal stimulation, and oropharyngeal anesthesia on corticobulbar and craniobulbar projections to human swallowing musculature. Changes in pathway excitability were measured via electromyography from swallowed intraluminal pharyngeal and esophageal electrodes to motor cerebral and trigeminal nerve magnetic stimulation. After both water swallowing and pharyngeal stimulation, pharyngoesophageal corticobulbar excitability increased (swallowing: pharynx = 59 +/- 12%, P < 0.001; esophagus = 45 +/- 20%, P < 0.05; pharyngeal stimulation: pharynx = 76 +/- 19%, P < 0.001; esophagus = 45 +/- 23%, P = 0.05), being early with swallowing but late with stimulation. By comparison, craniobulbar excitability increased early after swallowing but remained unaffected by pharyngeal stimulation. After anesthesia, both corticobulbar (pharynx =-24 +/- 10%, P < 0.05; esophagus = -28 +/- 7%, P < 0.01) and craniobulbar excitability showed a late decrease. Thus swallowing induces transient early facilitation of corticobulbar and craniobulbar projections, whereas electrical stimulation promotes delayed facilitation mainly in cortex. With removal of input, both corticobulbar and craniobulbar projections show delayed inhibition, implying a reduction in motoneuron and/or cortical activity.

Patterns of excitability in human esophageal sensorimotor cortex to painful and nonpainful visceral stimulation

To better understand the relationship between cortical plasticity and visceral pain, we developed a pain-induced model of altered esophageal corticobulbar excitability. In eight healthy volunteers, corticoesophageal electromyographic responses were recorded via an intraluminal catheter, following magnetic stimulation of the right sensorimotor cortex using perithreshold intensities. Corticothenar responses were used as control. Responses were assessed both before and for up to 1 h after either painful or nonpainful balloon distension of the esophagus (frequency = 1 Hz, dwell time = 200 ms, duration = 10 min), each being delivered to each subject in random order. Painful esophageal distension (mean volume = 11 +/- 3 ml) induced a profound increase in esophageal responses compared with baseline levels (at 30 min: 141 +/- 12 vs. 101 +/- 9 microV, P < 0.01), whereas nonpainful esophageal distension (mean volume = 4 +/- 2 ml) showed a decrease (at 30 min: 72 +/- 8 vs. 88 +/- 12 microV, P < 0.03). Thenar responses were unaffected. The results show that painful and nonpainful stimuli induce different patterns of esophageal corticobulbar excitability, suggesting a physiological link between cortical plasticity and visceral pain.

Sensorimotor modulation of human cortical swallowing pathways

1. Transcranial 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. 2. Comparison 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. 3. Single 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. 4. Single 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. 5. Cortical 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.