Functional connectivity and laterality of the motor and sensory components in the volitional swallowing network

Investigation of changes in the interaction of cerebral cortex during the oral swallowing task

BACKGROUND

The main swallowing activities in the oral phase include chewing and tongue movements. Cortical control is essential for the initiation and coordination of swallowing activities in the oral phase.

RESEARCH PURPOSES

This study aims to further investigate whether there are differences neural mechanisms in cortical interactions underlying oral phase by simulating chewing and tongue movement.

METHODS

This study recruited 25 healthy adult participants, by functional magnetic resonance imaging to collect data in the Empty chewing task and Tongue-to-Palate posterior Retraction task. The Dynamic causal modelling and Parametric Empirical Bayes were used to analyze the best model and the effective connectivity between brain regions under different tasks.

RESULTS

In the Empty Chewing task, the primary motor cortex(M1) is the main driving input brain area with significant excitatory connectivity with the primary somatosensory cortex(S1) and supplementary motor area(SMA). However, in the Tongue-to-Palate posterior Retraction task, S1 becomes the main driving input brain area and maintains bidirectional connections with M1 and SMA, but S1 shows an inhibitory effect on SMA.

CONCLUSION

This study reveals the differences in the interaction among brain regions during the oral swallowing activity. Results suggest M1 and SMA interaction is vital for the whole oral phase. M1 is a key brain region for Empty chewing task, while S1 is important for sensory feedback. S1 may inhibit SMA during the Tongue-to-Palate posterior Retraction task to aid swallowing and reduce interference with the pharyngeal swallowing action.

Revealing Goal-Directed Neural Control of the Pharyngeal Phase of Swallowing

Swallowing is considered a three-phase mechanism involving the oral, pharyngeal, and esophageal phases. The pharyngeal phase relies on highly coordinated movements in the pharynx and larynx to move food through the aerodigestive crossing. While the brainstem has been identified as the primary control center for the pharyngeal phase of swallowing, existing evidence suggests that the higher brain regions can contribute to controlling the pharyngeal phase of swallowing to match the motor response to the current context and task at hand. This suggests that the pharyngeal phase of swallowing cannot be exclusively reflexive or voluntary but can be regulated by the two neural controlling systems, goal-directed and non-goal-directed. This capability allows the pharyngeal phase of swallowing to adjust appropriately based on cognitive input, learned knowledge, and predictions. This paper reviews existing evidence and accordingly develops a novel perspective to explain these capabilities of the pharyngeal phase of swallowing. This paper aims (1) to integrate and comprehend the neurophysiological mechanisms involved in the pharyngeal phase of swallowing, (2) to explore the reflexive (non-goal-directed) and voluntary (goal-directed) neural systems of controlling the pharyngeal phase of swallowing, (3) to provide a clinical translation regarding the pathologies of these two systems, and (4) to highlight the existing gaps in this area that require attention in future research. This paper, in particular, aims to explore the complex neurophysiology of the pharyngeal phase of swallowing, as its breakdown can lead to serious consequences such as aspiration pneumonia or death.

Multimodal Adaptations to Expiratory Musculature-Targeted Resistance Training: A Preliminary Study in Healthy Young Adults

PURPOSE

Exercise-induced adaptations, including neuroplasticity, are well studied for physical exercise that targets skeletal muscles. However, little is known about the neuroplastic potential of targeted speech and swallowing exercises. The current study aimed to gather preliminary data on molecular and functional changes associated with the neuroplastic effects of 4-week expiratory musculature-targeted resistance training in healthy young adults.

METHOD

Five healthy young adult men aged between 19 and 35 years, M (SD) = 28.8 (2.68) years, underwent 4 weeks of expiratory muscle strength training (EMST). We measured changes in maximum expiratory pressure (MEP), serum brain-derived neurotrophic factor (BDNF), and insulin-like growth factor 1 (IGF-1) levels at baseline and posttraining conditions. Furthermore, functional and structural magnetic resonance images were obtained to investigate the neuroplastic effects of EMST. We analyzed the effects of training using a linear mixed model for each outcome, with fixed effects for baseline and posttraining.

RESULTS

MEP and serum BDNF levels significantly increased posttraining. However, this effect was not observed for IGF-1. A significant increase in functional activation in eight regions was also observed posttraining. However, we did not observe significant changes in the white matter microstructure.

CONCLUSIONS

Preliminary data from our study suggest targeted resistance training of expiratory muscles results in molecular and neuroplastic adaptations similar to exercise that targets skeletal muscles. Additionally, these results suggest that EMST could be a potential intervention to modulate (or prime) neurotrophic signaling pathways linked to functional strength gains and neuroplasticity.

The neurorehabilitation of post-stroke dysphagia: Physiology and pathophysiology

Swallowing is a complex process involving the precise contractions of numerous muscles of the head and neck, which act to process and shepherd ingested material from the oral cavity to its eventual destination, the stomach. Over the past five decades, information from animal and human studies has laid bare the complex network of neurones in the brainstem, cortex and cerebellum that are responsible for orchestrating each normal swallow. Amidst this complexity, problems can and often do occur that result in dysphagia, defined as impaired or disordered swallowing. Dysphagia is common, arising from multiple varied disease processes that can affect any of the neuromuscular structures involved in swallowing. Post-stroke dysphagia (PSD) remains the most prevalent and most commonly studied form of dysphagia and, as such, provides an important disease model to assess dysphagia physiology and pathophysiology. In this review, we explore the complex neuroanatomical processes that occur during normal swallowing and PSD. This includes how strokes cause dysphagia, the mechanisms through which natural neuroplastic recovery occurs, current treatments for patients with persistent dysphagia and emerging neuromodulatory treatments.

Cerebral small vessel disease is an independent determinant of dysphagia after acute stroke

BACKGROUND

The high incidence of dysphagia after acute stroke is likely the result of cumulative effects of the stroke and pre-stroke brain health. While cerebral small vessel disease (cSVD) is recognized as a marker of compromised brain health, it's unclear which neuroanatomical pathologies of cSVD impact post-stroke dysphagia. We assessed the relation between cSVD pathologies, i.e., brain atrophy, white matter hyperintensities (WMH), perivascular spaces, as markers for brain integrity at the time of the stroke, and acute post-stroke dysphagia measured with the Modified Barium Swallow Study (MBSS).

METHODS

We conducted a retrospective, observational study of 40 individuals with an acute first-ever ischemic stroke. We segmented T1-weighted images into gray matter, white matter, and cerebrospinal fluid (CSF) to derive brain atrophy estimates. We scored the presence and severity of periventricular and deep WMH using the Fazekas scale and counted perivascular spaces in the basal ganglia following standard guidelines. Swallow impairments were determined with the Modified Barium Swallow Impairment Profile (MBSImP), Penetration-Aspiration Scale, and timing measures (oral (OTT), and pharyngeal transit times (PTT)). We performed regression to assess the relation between cSVD pathologies and swallowing while controlling for the stroke overlap with the right and left corticobulbar tracts, stroke volume, and the number of days between the MRI and MBSS.

RESULTS

Worse brain atrophy and more severe periventricular WMH were related to more severe MBSImP pharyngeal total scores, and worse deep WMH were related to aspiration events. More severe perivascular spaces in the basal ganglia were related to longer OTT and PTT, with a high explanatory value (27.5% and 25.1%, respectively), even when controlling for chronological age.

CONCLUSIONS

Our results suggest that several aspects of pre-stroke brain health impact dysphagia severity after acute stroke independent of the stroke site and size. These findings contribute to our understanding of mechanisms underlying the variability of post-stroke dysphagia and emphasize the importance of brain structural integrity before the stroke. Future larger studies are warranted.

Cortical compensation mechanism for swallowing recovery in patients with medullary infarction-induced dysphagia

Introduction

This study aims to examine brain activity during different swallowing actions in patients with dysphagia caused by medullary infarction (MI) before and after treatment using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging.

Methods

Fifteen patients were enrolled in this study. Brain activation during saliva swallowing and effortful saliva swallowing was observed using BOLD imaging in the acute phase of stroke and after 4 weeks of rehabilitation training. Differences in the activation of brain regions during saliva swallowing before and after treatment, during effortful saliva swallowing before and after treatment, and between the two swallowing actions before and after treatment were compared.

Results

In the acute phase of stroke, only the bilateral precentral and left lingual gyrus were partially activated during saliva swallowing, and there was no obvious activation in the insula. Effortful saliva swallowing activated more brain regions than saliva swallowing before treatment, including the bilateral supplementary motor area (SMA), postcentral gyrus, and right insular cortex. The number of brain regions activated during saliva swallowing increased after treatment, including the bilateral precentral gyrus, postcentral gyrus, insula, thalamus, and SMA.

Discussion

Cortical activation increases after recovery from dysphagia, and the increased activation of the postcentral gyrus might play a functional compensatory role. Effortful saliva swallowing is a more effective rehabilitation training method for patients with dysphagia caused by MI.

Swallowing dysfunctions in patients with disorders of consciousness: Evidence from neuroimaging data, assessment, and management

Following severe brain injuries, a subset of patients may remain in an altered state of consciousness; most of these patients require artificial feeding. Currently, a functional oral phase and the presence of exclusive oral feeding may constitute signs of consciousness. Additionally, the presence of pharyngo-laryngeal secretions, saliva aspiration, cough reflex and tracheostomy are related to the level of consciousness. However, the link between swallowing and consciousness is yet to be fully understood. The primary aim of this review is to establish a comprehensive overview of the relationship between an individual's conscious behaviour and swallowing (reflexive and voluntary). Previous studies of brain activation during volitional and non-volitional swallowing tasks in healthy subjects are also reviewed. We demonstrate that the areas activated by voluntary swallowing tasks (primary sensorimotor, cingulate, insula, premotor, supplementary motor, cerebellum, and operculum) are not specific to deglutitive function but are shared with other motor tasks and brain networks involved in consciousness. This review also outlines suitable assessment and treatment methods for dysphagic patients with disorders of consciousness. Finally, we propose that markers of swallowing could contribute to the development of novel diagnostic guidelines for patients with disorders of consciousness.

Transcranial direct current stimulation for post-stroke dysphagia: a meta-analysis

BACKGROUND

Strokes may cause some swallowing difficulty or associated dysphagia in 25-80% of patients. This phenomenon has been linked to increased morbidity and mortality. Therefore, the aim of this study was to evaluate the efficacy of transcranial direct current stimulation in patients with dysphagia in post-stroke patients.

METHODS

A systematic search in PubMed, Scopus, Web of Science and MEDLINE was conducted. The articles must have to evaluate an intervention that included transcranial direct current stimulation; the sample had to consist exclusively of patients with post-stroke dysphagia; and the experimental design consisted of randomized controlled trial. Difference in mean differences and their 95% confidence interval were calculated as the between-group difference in means divided by the pooled standard deviation. The I2 statistic was used to determine the degree of heterogeneity.

RESULTS

Of the 9 investigations analyzed, all applied transcranial direct current stimulation in combination with conventional dysphagia therapy to the experimental group. All the studies analyzed identified improvements in swallowing function and meta-analysis confirmed their strong effect on reducing the risk of penetration and aspiration (Hedges's g = 0.55). The results showed that participants who received transcranial direct current stimulation significantly improved swallowing function.

CONCLUSIONS

Transcranial direct current stimulation has positive effects in the treatment of poststroke dysphagia by improving swallowing function, oral and pharyngeal phase times and the risk of penetration and aspiration. Furthermore, its combination with conventional dysphagia therapy, balloon dilatation with catheter or training of the swallowing muscles ensures improvement of swallowing function. PROSPERO registration ID CRD42022314949.

Multiple Sclerosis Is Associated With Achalasia and Diffuse Esophageal Spasm

Background/Aims

Multiple sclerosis (MS) is an inflammatory disease characterized by the demyelination of primarily the central nervous system. Diffuse esophageal spasm (DES) and achalasia are both disorders of esophageal peristalsis which cause clinical symptoms of dysphagia. Mechanisms involving dysfunction of the pre- and post-ganglionic nerve fibers of the myenteric plexus have been proposed. We sought to determine whether MS confers an increased risk of developing achalasia or DES.

Methods

Cohort analysis was done using the Explorys database. Univariate logistic regression was performed to determine the odds MS confers to each motility disorder studied. Comparison of proportions of dysautonomia comorbidities was performed among the cohorts. Patients with a prior diagnosis of diabetes mellitus, chronic Chagas' disease, opioid use, or CREST syndrome were excluded from the study.

Results

Odds of MS patients developing achalasia or DES were (OR, 2.09; 95% CI, 1.73-2.52; P < 0.001) and (OR, 3.15; 95% CI, 2.89-3.42; P < 0.001), respectively. In the MS/achalasia cohort, 27.27%, 18.18%, 9.09%, and 45.45% patients had urinary incontinence, gastroparesis, impotence, and insomnia, respectively. In the MS/DES cohort, 35.19%, 11.11%, 3.70%, and 55.56% had these symptoms. In MS patients without motility disorders, 12.64%, 0.79%, 2.21%, and 21.85% had these symptoms.

Conclusions

Patients with MS have higher odds of developing achalasia or DES compared to patients without MS. MS patients with achalasia or DES have higher rates of dysautonomia comorbidities. This suggests that these patients have a more severe disease phenotype in regards to the extent of neuronal degradation and demyelination causing the autonomic dysfunction.

Cerebral control of swallowing: An update on neurobehavioral evidence

This review aims to update the current knowledge on the cerebral control of swallowing. We review data from both animal and human studies spanning across the fields of neuroanatomy, neurophysiology and neuroimaging to evaluate advancements in our understanding in the brain's role in swallowing. Studies have collectively shown that swallowing is mediated by multiple distinct cortical and subcortical regions and that lesions to these regions can result in dysphagia. These regions are functionally connected in separate groups within and between the two hemispheres. While hemispheric dominance for swallowing has been reported in most human studies, the laterality is inconsistent across individuals. Moreover, there is a shift in activation location and laterality between swallowing preparation and execution, although such activation changes are less well-defined than that for limb motor control. Finally, we discussed recent neurostimulation treatments that may be beneficial for dysphagia after brain injury through promoting the reorganization of the swallowing neural network.

Effects of dual-task interference on swallowing in healthy aging adults

A wide body of literature has demonstrated that the neural representation of healthy swallowing is mostly bilateral, with one hemisphere dominant over the other. While several studies have demonstrated the presence of laterality for swallowing related functions among young adults, the data on older adults are still growing. The purpose of this paper is to investigate potential changes in hemispheric dominance in healthy aging adults for swallowing related tasks using a behavioral dual-task paradigm. A modified dual-task paradigm was designed to investigate the potential reduction in hemispherical specialization for swallowing function. Eighty healthy right-handed participants in the study were divided into two groups [Group 1: young adults (18–40 years) and Group 2: older adults (65 and above)]. All the participants performed a timed water swallow test at baseline and with two interference conditions (silent word repetition, and facial recognition). The results of the study revealed the following 1) a statistically significant effect of age on swallow performance; 2) statistically significant effect of each of the interference tasks on two of the swallow measures (VPS and VPT) in younger adults; and 3) no significant effect of the interference tasks on the swallowing performance of older adults. These findings suggest that aging substantially affects swallowing in older individuals, and this potentially accompanies a reduction in the hemispheric specialization for swallowing related tasks.

Repetitive Transcranial Magnetic Stimulation at Different Sites for Dysphagia After Stroke: A Randomized, Observer-Blind Clinical Trial

Background: The clinical efficacy of repetitive transcranial magnetic stimulation (rTMS) protocols on patients with poststroke dysphagia is still unclear.

Objective: This trial aimed to explore and analyze the effectiveness of 5 Hz rTMS on the unaffected hemisphere, affected hemisphere, and cerebellum in stroke patients with dysphagia.

Methods: This observer-blind and randomized controlled trial included a total of 147 patients with stroke. Patients were divided into four treatment groups: the unaffected hemispheric group, the affected hemispheric group, the cerebellum group and the control group. Each group received traditional dysphagia treatment 5 days a week for 2 weeks. All recruited patients except for those in the control group underwent 10 consecutive rTMS sessions for 2 weeks. For the affected hemispheric group and unaffected hemispheric group, 5 Hz rTMS was applied to the affected mylohyoid cortical region or to the unaffected mylohyoid cortical region. For the cerebellum group, 5 Hz rTMS was applied to the mylohyoid cortical representation of the cerebellum (4.3 cm lateral and 2.4 cm below the inion). The Fiberoptic Endoscopic Dysphagia Severity Scale (FEDSS), Penetration/Aspiration Scale (PAS), Gugging Swallowing Screen (GUSS), and Standardized Swallowing Assessment (SSA) were used to evaluate clinical swallowing function before the intervention (baseline), immediately after the intervention and 2 weeks after the intervention.

Results: There were significant time and intervention interaction effects on the FEDSS, PAS, SSA, and GUSS scores (p < 0.05). In a direct comparison of the swallowing parameters of the four groups, the changes in FEDSS, PAS, SSA, and GUSS scores showed a significantly greater improvement in the unaffected hemispheric group, the affected hemispheric group and cerebellum group than in the control group (p < 0.05).

Conclusions: Whether stimulating the unaffected hemisphere or the affected hemisphere, 5 Hz high-frequency rTMS on mylohyoid cortical tissue might have a positive effect on poststroke patients with dysphagia. In addition, cerebellar rTMS is a safe method that represents a potential treatment for poststroke dysphagia, and more clinical trials are needed to develop this technique further.

Clinical Trial Registration:chictr.org.cn, identifier: ChiCTR2000032255.

Association of Lesion Pattern and Dysphagia in Acute Intracerebral Hemorrhage

[Figure: see text].

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

BACKGROUND

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.

METHODS

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 30 seconds of 15 and 36°C applied to the tongue surface for either 10 minutes, 5 minutes, or sham. In the second experiment, one of three intermittent thermal stimulus patterns was delivered: cold (alternating 30 seconds of 15 and 36°C), warm (continuous 36°C), or hot (alternating 30 seconds of 45 and 36°C) for 10 minutes. In both experiments, PMEP were remeasured every 15 minutes up to 60 minutes following thermal stimulation.

KEY RESULTS

Repeated measures ANOVA for each stimulus time in the first experiment showed a significant increased change in PMEP amplitude at 30 minutes 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.

CONCLUSIONS AND INFERENCES

Ten-minute cold stimulation on the tongue can induce a delayed (30 minutes) increase in pharyngeal cortical excitability, providing a clinically useful therapeutic window for its application in dysphagic patients.

Ischemic Lesion Location Based on the ASPECT Score for Risk Assessment of Neurogenic Dysphagia

Dysphagia is common in patients with middle cerebral artery (MCA) infarctions and associated with malnutrition, pneumonia, and mortality. Besides bedside screening tools, brain imaging findings may help to timely identify patients with swallowing disorders. We investigated whether the Alberta stroke program early CT score (ASPECTS) allows for the correlation of distinct ischemic lesion patterns with dysphagia. We prospectively examined 113 consecutive patients with acute MCA infarctions. Fiberoptic endoscopic evaluation of swallowing (FEES) was performed within 24 h after admission for validation of dysphagia. Brain imaging (CT or MRI) was rated for ischemic changes according to the ASPECT score. 62 patients (54.9%) had FEES-proven dysphagia. In left hemispheric strokes, the strongest associations between the ASPECTS sectors and dysphagia were found for the lentiform nucleus (odds ratio 0.113 [CI 0.028–0.433; p = 0.001), the insula (0.275 [0.102–0.742]; p = 0.011), and the frontal operculum (0.280 [CI 0.094–0.834]; p = 0.022). A combination of two or even all three of these sectors together increased relative dysphagia frequency up to 100%. For right hemispheric strokes, only non-significant associations were found which were strongest for the insula region. The distribution of early ischemic changes in the MCA territory according to ASPECTS may be used as risk indicator of neurogenic dysphagia in MCA infarction, particularly when the left hemisphere is affected. However, due to the exploratory nature of this research, external validation studies of these findings are warranted in future.

Targeting the sensory feedback within the swallowing network-Reversing artificially induced pharyngolaryngeal hypesthesia by central and peripheral stimulation strategies

Pharyngolaryngeal hypesthesia is a major reason for dysphagia in various neurological diseases. Emerging neuromodulation devices have shown potential to foster dysphagia rehabilitation, but the optimal treatment strategy is unknown. Because functional imaging studies are difficult to conduct in severely ill patients, we induced a virtual sensory lesion in healthy volunteers and evaluated the effects of central and peripheral neurostimulation techniques. In a sham-controlled intervention study with crossover design on 10 participants, we tested the potential of (peripheral) pharyngeal electrical stimulation (PES) and (central) transcranial direct current stimulation (tDCS) to revert the effects of lidocaine-induced pharyngolaryngeal hypesthesia on central sensorimotor processing. Changes were observed during pharyngeal air-pulse stimulation and voluntary swallowing applying magnetoencephalography before and after the interventions. PES induced a significant (p < .05) increase of activation during swallowing in the bihemispheric sensorimotor network in alpha and low gamma frequency ranges, peaking in the right premotor and left primary sensory area, respectively. With pneumatic stimulation, significant activation increase was found after PES in high gamma peaking in the left premotor area. Significant changes of brain activation after tDCS could neither be detected for pneumatic stimulation nor for swallowing. Due to the peripheral cause of dysphagia in this model, PES was able to revert the detrimental effects of reduced sensory input on central processing, whereas tDCS was not. Results may have implications for therapeutic decisions in the clinical context.

Cortical and Subcortical Control of Swallowing-Can We Use Information From Lesion Locations to Improve Diagnosis and Treatment for Patients With Stroke?

Purpose Swallowing is a complex process, mediated by a broad bilateral neural network that spans from the brainstem to subcortical and cortical brain structures. Although the cortex's role in swallowing was historically neglected, we now understand, especially through clinical observations and research of patients with stroke, that it substantially contributes to swallowing control. Neuroimaging techniques (e.g., magnetic resonance imaging) have helped significantly to elucidate the role of cortical and subcortical brain areas, in general, and the importance of specific areas in swallowing control in healthy individuals and patients with stroke. We will review recent discoveries in cortical and subcortical neuroimaging research studies and their generalizability across patients to discuss their potential implications and translation to dysphagia diagnosis and treatment in clinical practice. Conclusions Stroke lesion locations have been identified that are commonly associated across patients with the occurrence and recovery of dysphagia, suggesting that clinical brain scans provide useful information for improving the diagnosis and treatment of patients with stroke. However, individual differences in brain structure and function limit the generalizability of these relationships and emphasize that the extent of the motor and sensory pathology in swallowing, and how the patient recovers, also depends on a patient's individual brain constitution. The involvement of the damaged brain tissue in swallowing control before the stroke and the health of the residual, undamaged brain tissue are crucial factors that can differ between individuals.

Model-Based and Model-Free Analyses of the Neural Correlates of Tongue Movements

The tongue performs movements in all directions to subserve its diverse functions in chewing, swallowing, and speech production. Using task-based functional MRI in a group of 17 healthy young participants, we studied (1) potential differences in the cerebral control of frontal (protrusion), horizontal (side to side), and vertical (elevation) tongue movements and (2) inter-individual differences in tongue motor control. To investigate differences between different tongue movements, we performed voxel-wise multiple linear regressions. To investigate inter-individual differences, we applied a novel approach, spatio-temporal filtering of independent components. For this approach, individual functional data were decomposed into spatially independent components and corresponding time courses using independent component analysis. A temporal filter (correlation with the expected brain response) was used to identify independent components time-locked to the tongue motor tasks. A spatial filter (cross-correlation with established neurofunctional systems) was used to identify brain activity not time-locked to the tasks. Our results confirm the importance of an extended bilateral cortical and subcortical network for the control of tongue movements. Frontal (protrusion) tongue movements, highly overlearned movements related to speech production, showed less activity in the frontal and parietal lobes compared to horizontal (side to side) and vertical (elevation) movements and greater activity in the left frontal and temporal lobes compared to vertical movements (cluster-forming threshold of Z > 3.1, cluster significance threshold of p < 0.01, corrected for multiple comparisons). The investigation of inter-individual differences revealed a component representing the tongue primary sensorimotor cortex time-locked to the task in all participants. Using the spatial filter, we found the default mode network in 16 of 17 participants, the left fronto-parietal network in 16, the right fronto-parietal network in 8, and the executive control network in four participants (Pearson's r > 0.4 between neurofunctional systems and individual components). These results demonstrate that spatio-temporal filtering of independent components allows to identify individual brain activity related to a specific task and also structured spatiotemporal processes representing known neurofunctional systems on an individual basis. This novel approach may be useful for the assessment of individual patients and results may be related to individual clinical, behavioral, and genetic information.

Functional Adaptation of Oromotor Functions and Aging: A Focused Review of the Evidence From Brain Neuroimaging Research

“Practice makes perfect” is a principle widely applied when one is acquiring a new sensorimotor skill to cope with challenges from a new environment. In terms of oral healthcare, the traditional view holds that restoring decayed structures is one of the primary aims of treatment. This assumes that the patient’s oromotor functions would be recovered back to normal levels after the restoration. However, in older patients, such a structural–functional coupling after dental treatment shows a great degree of individual variations. For example, after prosthodontic treatment, some patients would adapt themselves quickly to the new dentures, while others would not. In this Focused Review, I argue that the functional aspects of adaptation—which would be predominantly associated with the brain mechanisms of cognitive processing and motor learning—play a critical role in the individual differences in the adaptive behaviors of oromotor functions. This thesis is critical to geriatric oral healthcare since the variation in the capacity of cognitive processing and motor learning is critically associated with aging. In this review, (a) the association between aging and the brain-stomatognathic axis will be introduced; (b) the brain mechanisms underlying the association between aging, compensatory behavior, and motor learning will be briefly summarized; (c) the neuroimaging evidence that suggests the role of cognitive processing and motor learning in oromotor functions will be summarized, and critically, the brain mechanisms underlying mastication and swallowing in older people will be discussed; and (d) based on the current knowledge, an experimental framework for investigating the association between aging and the functional adaptation of oromotor functions will be proposed. Finally, I will comment on the practical implications of this framework and postulate questions open for future research.

Thirst and Drinking Paradigms: Evolution from Single Factor Effects to Brainwide Dynamic Networks

The motivation to seek and consume water is an essential component of human fluid–electrolyte homeostasis, optimal function, and health. This review describes the evolution of concepts regarding thirst and drinking behavior, made possible by magnetic resonance imaging, animal models, and novel laboratory techniques. The earliest thirst paradigms focused on single factors such as dry mouth and loss of water from tissues. By the end of the 19th century, physiologists proposed a thirst center in the brain that was verified in animals 60 years later. During the early- and mid-1900s, the influences of gastric distention, neuroendocrine responses, circulatory properties (i.e., blood pressure, volume, concentration), and the distinct effects of intracellular dehydration and extracellular hypovolemia were recognized. The majority of these studies relied on animal models and laboratory methods such as microinjection or lesioning/oblation of specific brain loci. Following a quarter century (1994–2019) of human brain imaging, current research focuses on networks of networks, with thirst and satiety conceived as hemispheric waves of neuronal activations that traverse the brain in milliseconds. Novel technologies such as chemogenetics, optogenetics, and neuropixel microelectrode arrays reveal the dynamic complexity of human thirst, as well as the roles of motivation and learning in drinking behavior.

The Initiation of Swallowing Can Indicate the Prognosis of Disorders of Consciousness: A Self-Controlled Study

Objective: To detect the initiation of swallowing in patients with disorders of consciousness (DOC) as well as the relationship between the initiation of swallowing and the prognosis of DOC patients. Methods: Nineteen DOC patients were included in this study, and a self-controlled trial compared five different stimuli. The five different stimuli were as follows: (1) one command, as recommended by the Coma Recovery Scale-Revised (CRS-R), which was "open your mouth"; (2) placing a spoon in front of the patient's mouth without a command; (3) placing a spoon filled with water in front of the patient's mouth without a command; (4) one command-"there is a spoon; open your mouth"-with a spoon in front of the patient's mouth; (5) one command, "there is a spoon with water; open your mouth," with a spoon filled with water in front of the patient's mouth. All 19 patients were given these five stimuli randomly, and any one of the commands was presented four times to a patient, one at a time, at 15-s intervals. The sensitivity and specificity of the initiation of swallowing in detecting conscious awareness were determined. Results: None of the patients responded to the first four stimuli. However, six patients showed initiated swallowing toward the fifth stimulus. Among those six, five patients showed improvement in their consciousness state 6 months later. The sensitivity and specificity of the initiation of swallowing for DOC patients was 83.33% [95% CIs (36%, 100%)] and 92.31% [95% CIs (64%, 100%)], respectively. Conclusions: The initiation of swallowing can be an early indication of conscious behavior and can likely provide evidence of conscious awareness. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03508336; Date of registration: 2018/4/16.

Comparison Between Automatic and Volitional Swallow in Healthy Individuals Using Tongue Array and Cervical Auscultation Modules

In healthy normal individuals, the act of swallowing can be performed volitionally or can occur spontaneously. Several attempts have been made to look into the possible differences that might exist between automatic swallow (AS) and volitional swallow (VS). The present study is an attempt to physiologically differentiate AS from that of VS, using combined modules of tongue array and cervical auscultation of Digital Swallowing Workstation. 15 males and 15 female participants in the age range of 18-25 participated in the present study. They performed an AS task and a VS task. These were analyzed for parameters of maximum amplitude, duration and pressure. The result of the study revealed higher values for all the parameters of VS, but a statistically significant difference only for the duration parameter of cervical auscultation. This finding leads to the impression that the duration of vocal fold closure plays a major role in airway protection. Similar interesting findings on effect of gender and nature and organization of AS and VS have been discussed.

The Effect of High-Frequency Repetitive Transcranial Magnetic Stimulation on Advancing Parkinson’s Disease With Dysphagia: Double Blind Randomized Clinical Trial

We investigate if rTMS has a therapeutic role in the treatment of dysphagia in patients with Parkinson’s disease (PD). Material and Methods. Thirty-three patients with PD and dysphagia were randomly classified with ratio 1:2 to receive sham or real rTMS (2000 pulses; 20 Hz; 90% resting motor threshold; 10 trains of 10 seconds with 25 seconds between each train) over the hand area of each motor cortex (5 minutes between hemispheres) for 10 days (5 days per week) followed by 5 booster sessions every month for 3 months. Assessments included the Unified Parkinson’s Disease Rating Scale part III (UPDRS), Instrumental Activities of Daily Living (IADL), and Arabic–Dysphagia Handicap Index (A-DHI) before, after the last session, and 3 months later. Video-fluoroscopy measures of pharyngeal transit time (PTT) and time to maximal hyoid elevation (H1-H2) were taken before and after the treatment sessions. Results. There were no significant differences between groups. There was a significant improvement on all rating scales (analysis of variance) after real rTMS with a significant time × group interaction. In particular, there was a significant and long-lasting (3 months) effect of time on all subitems of the A-DHI (functional, P = .0001; physical, P = .0001; emotional, P = .02) but not in the sham group. This was associated with significant improvement in H1-H2 ( P = .03) and PTT ( P = .01) during solid swallows in the real rTMS but not the sham group. Conclusion. Real rTMS improves dysphagia in PD as documented by A-DHI scores and by video-fluoroscopy.

Factors Influencing Oral Intake Improvement and Feeding Tube Dependency in Patients with Poststroke Dysphagia

OBJECTIVE

To assess ischemic stroke patients regarding the relationship between lesion locations, swallowing impairment, medical and demographic factors and (1) oral intake improvement and (2) feeding tube dependency at discharge from their acute hospital stay.

METHODS

We conducted an exploratory, retrospective observational longitudinal cohort study of acute, first-ever, ischemic stroke patients. Patients who had an initial nonoral feeding recommendation from a speech and language pathologist and who underwent a modified barium swallow study within their hospital stay were included. Oral intake status was measured with the Functional Oral Intake Scale (FOIS) as the change in FOIS during the hospital stay and as feeding tube dependency at hospital discharge. Associations were assessed with multiple linear regression modeling controlling for age, comorbidities, and hospital length of stay.

RESULTS

We included 44 stroke patients. At hospital discharge, 93% of patients had oral intake restrictions and 30% were feeding tube dependent. Following multiple linear regression modeling, age, damage to the left superior frontal gyrus, dorsal anterior cingulate gyrus, hypothalamus, and nucleus accumbens were significant predictors for FOIS change. Feeding tube dependency showed no significant associations with any prognostic variables when controlling for confounders.

CONCLUSIONS

The vast majority of patients with an initial nonoral feeding recommendation are discharged with oral intake restrictions indicating a continued need for swallowing assessments and treatment after discharge. Lesion locations associated with motivation, reward, and drive to consume food as well as swallowing impairment, higher age, and more comorbidities were related to less oral intake improvement.

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

BACKGROUND

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.

METHODS

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.

KEY RESULTS

Two-way repeated measures ANOVA with factors of Temperature × Trial in amplitude of MEP demonstrated a significant effect of Temperature both in the stronger (F_2,34  = 5.775, P = .007) and weaker (F_2,34  = 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).

CONCLUSIONS & INFERENCES

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.

Differences in swallow physiology in patients with left and right hemispheric strokes

BACKGROUND

We sought to determine the impact of lesion lateralization and lesion volume on swallow impairment on group-level by comparing patients with left and right hemisphere strokes and on patient-level by analyzing patients individually.

METHODS

We performed a retrospective, observational, cross-sectional study of 46 patients with unilateral (22 left, 24 right), acute, first-ever, ischemic strokes who received a diffusion weighted MRI (DW-MRI) and modified barium swallow study (MBSS) during their acute hospital stay. We determined lesion side on the DW-MRI and measured swallow physiology using the Modified Barium Swallow Impairment Profile (MBSImP™©), Penetration-Aspiration Scale (PAS), swallow timing, distance, area, and speed measures. We performed Pearson's Chi-Square and Wilcoxon Rank-Sum tests to compare patients with left and right hemisphere strokes, and Pearson or Spearman correlation, simple logistic regression, linear, and logistic multivariable regression modeling to assess the relationship between variables.

RESULTS

At the group-level, there were no differences in MBSImP oral swallow impairment scores between patients with left and right hemisphere stroke. In adjusted analyses, patients with right hemisphere strokes showed significantly worse MBSImP pharyngeal total scores (p = 0.02), worse MBSImP component specific scores for laryngeal vestibular closure (Bonferroni adjusted alpha p ≤ 0.0029), and worse PAS scores (p = 0.03). Patients with right hemisphere strokes showed worse timing, distance, area, and speed measures. Lesion volume was significantly associated with MBSImP pharyngeal residue (p = 0.03) and pharyngeal total scores (p = 0.04). At the patient-level, 24% of patients (4 left, 7 right) showed opposite patterns of MBSImP oral and pharyngeal swallow impairment than seen at group-level.

CONCLUSION

Our study showed differences in swallow physiology between patients with right and left unilateral strokes with patients with right hemisphere strokes showing worse pharyngeal impairment. Lesion lateralization seems to be a valuable marker for the severity of swallowing impairment at the group-level but less informative at the patient-level.

Dual Transcranial Direct Current Stimulation for Poststroke Dysphagia: A Randomized Controlled Trial

BACKGROUND

Poststroke dysphagia is associated with considerable morbidity and has high health care cost implications.

OBJECTIVE

To evaluate whether anodal transcranial direct current stimulation (tDCS) over the lesioned hemisphere and cathodal tDCS to the contralateral one during the early stage of rehabilitation can improve poststroke dysphagia.

METHODS

A total of 40 patients referred to our neurorehabilitation department were randomized to receive anodal tDCS over the damaged hemisphere plus cathodal stimulation over the contralateral one versus sham stimulation during swallowing maneuvers over the course of 10 sessions of treatment. Swallowing function was evaluated before and after stimulation using the Dysphagia Outcome and Severity Scale (DOSS).

RESULTS

The percentage of patients who reached various thresholds of improvement was higher in the tDCS group than in the sham group, but the differences were not significant (eg, DOSS score ≥ 20% increase from baseline: 55% in the tDCS group vs 40% in the sham group; P = .53). Among all variables recorded at baseline, only a subgroup of patients without nasogastric tube showed a significantly higher improvement with tDCS treatment versus sham (DOSS score ≥10% and ≥20% from baseline: 64.29% vs 0%, P = .01).

CONCLUSIONS

In patients with poststroke dysphagia, treatment with dual tDCS in the early phase of rehabilitation does not significantly increase the probability of recovery compared with sham stimulation.

Novel Mealtime Duration Measures: Reliability and Preliminary Associations With Clinical Feeding and Swallowing Performance in Self-Feeding Children With Cerebral Palsy

PURPOSE

The purpose of this study is to examine (a) the reliability of newly developed measures of mealtime duration and (b) their relationship to clinical feeding/swallowing performance in children with spastic cerebral palsy (SCP).

METHOD

Seventeen self-feeding children (9 boys, 8 girls) with SCP (age range = 5;1 [years;months] to 17;6, Gross Motor Function Classification System range = I-IV) were assessed during mealtimes using the Dysphagia Disorder Survey (DDS; Sheppard, Hochman, & Baer, 2014). Children were divided into 2 groups, children with primarily unilateral or bilateral brain involvement. Duration measures included mealtime duration and total sip/bite duration for each bolus type (liquid and solid).

RESULTS

Excellent intra- and inter-rater reliability for all duration measures was observed (intraclass correlation coefficient [ICC] = 1.00 and 0.955, respectively, for mealtime duration; ICC = 1.00 and 0.963, respectively, for solid/bite duration; ICC = 1.00 and 0.957, respectively, for liquid/sip duration). Positive correlations were found between total mealtime duration and DDS Part 1, rs = .514 [.045-.797], p = .035; Part 2, rs = .528 [.064-.804], p = .029; and total scores, rs = .665 [.271-.868], p = .004, and between total solid/bite duration and DDS Part 1, rs = .579 [.137-.828], p = .015; Part 2, rs = .620 [.199-.847], p = .007; and total scores, rs = .762 [.444-.909], p < .001. Children with unilateral brain involvement exhibited significantly lower DDS total (p = .049) and Part 2 scores (p = .026), indicating better feeding/swallowing performance/skills. They also had shorter mealtime duration (p = .019) and solid/bite duration (p = .025) compared with children with bilateral involvement.

CONCLUSIONS

Our new mealtime duration measures are reliable and correlate with feeding/swallowing performance in a sample of self-feeding children with SCP. Therefore, they may be useful supplements to feeding/swallowing assessments for this population.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.5715076.

Randomized trial of transcranial direct current stimulation for poststroke dysphagia

OBJECTIVE

We evaluated whether transcranial direct current stimulation (tDCS) is able to enhance dysphagia rehabilitation following stroke. Besides relating clinical effects with neuroplastic changes in cortical swallowing processing, we aimed to identify factors influencing treatment success.

METHODS

In this double-blind, randomized study, 60 acute dysphagic stroke patients received contralesional anodal (1mA, 20 minutes) or sham tDCS on 4 consecutive days. Swallowing function was thoroughly assessed before and after the intervention using the validated Fiberoptic Endoscopic Dysphagia Severity Scale (FEDSS) and clinical assessment. In 10 patients, swallowing-related brain activation was recorded applying magnetoencephalography before and after the intervention. Voxel-based statistical lesion pattern analysis was also performed.

RESULTS

Study groups did not differ according to demographic data, stroke characteristics, or baseline dysphagia severity. Patients treated with tDCS showed greater improvement in FEDSS than the sham group (1.3 vs 0.4 points, mean difference = 0.9, 95% confidence interval [CI] = 0.4-1.4, p < 0.0005). Functional recovery was accompanied by a significant increase of activation (p < 0.05) in the contralesional swallowing network after real but not sham tDCS. Regarding predictors of treatment success, for every hour earlier that treatment was initiated, there was greater improvement on the FEDSS (adjusted odds ratio = 0.99, 95% CI = 0.98-1.00, p < 0.05) in multivariate analysis. Stroke location in the right insula and operculum was indicative of worse response to tDCS (p < 0.05).

INTERPRETATION

Application of tDCS over the contralesional swallowing motor cortex supports swallowing network reorganization, thereby leading to faster rehabilitation of acute poststroke dysphagia. Early treatment initiation seems beneficial. tDCS may be less effective in right-hemispheric insulo-opercular stroke. Ann Neurol 2018;83:328-340.

Task-Correlated Cortical Asymmetry and Intra- and Inter-Hemispheric Separation

Cerebral lateralization is expressed at both the structural and functional levels, and can exist as either a stable characteristic or as a dynamic feature during behavior and development. The anatomically relatively simple olfactory system demonstrates lateralization in both human and non-human animals. Here, we explored functional lateralization in both primary olfactory cortex - a region critical for odor memory and perception- and orbitofrontal cortex (OFC) - a region involved in reversal learning- in rats performing an odor learning and reversal task. We find significant asymmetry in both olfactory and orbitofrontal cortical odor-evoked activity, which is expressed in a performance- and task-dependent manner. The emergence of learning-dependent asymmetry during reversal learning was associated with decreased functional connectivity both between the bilateral OFC and between the OFC-olfactory cortex. The results suggest an inter-hemispheric asymmetry and olfactory cortical functional separation that may allow multiple, specialized processing circuits to emerge during a reversal task requiring behavioral flexibility.

Increased insula-putamen connectivity in X-linked dystonia-parkinsonism

Preliminary evidence from postmortem studies of X-linked dystonia-parkinsonism (XDP) suggests tissue loss may occur first and/or most severely in the striatal striosome compartment, followed later by cell loss in the matrix compartment. However, little is known about how this relates to pathogenesis and pathophysiology. While MRI cannot visualize these striatal compartments directly in humans, differences in relative gradients of afferent cortical connectivity across compartments (weighted toward paralimbic versus sensorimotor cortex, respectively) can be used to infer potential selective loss in vivo. In the current study we evaluated relative connectivity of paralimbic versus sensorimotor cortex with the caudate and putamen in 17 individuals with XDP and 17 matched controls. Although caudate and putamen volumes were reduced in XDP, there were no significant reductions in either “matrix-weighted”, or “striosome-weighted” connectivity. In fact, paralimbic connectivity with the putamen was elevated, rather than reduced, in XDP. This was driven most strongly by elevated putamen connectivity with the anterior insula. There was no relationship of these findings to disease duration or striatal volume, suggesting insula and/or paralimbic connectivity in XDP may develop abnormally and/or increase in the years before symptom onset.

•

Previous work suggested striosomes might degenerate preferentially in early XDP.

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We developed a DTI tractography method to assess striosome and matrix integrity.

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Striosomal afferents to putamen were elevated in XDP, despite reduced putamen volume.

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Connectivity was particularly elevated from the insula (two to three-fold).

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Striosome connectivity strength was not associated with disease duration.

Lesions Responsible for Delayed Oral Transit Time in Post-stroke Dysphagia

INTRODUCTION

Some stroke patients show oral phase dysphagia, characterized by a markedly prolonged oral transit time that hinders oral feeding. The aim of this study was to clarify the clinical characteristics and lesions responsible for delayed swallowing.

METHODS

We reviewed 90 patients with stroke. The oral processing time plus the postfaucial aggregation time required to swallow semisolid food was assessed. The patients were divided into two groups according to oral transit time, and we analyzed the differences in characteristics such as demographic factors, lesion factors, and cognitive function. Logistic regression analyses were performed to examine the predictors of delayed oral transit time. Lesion location and volume were measured on brain magnetic resonance images. We generated statistic maps of lesions related to delayed oral phase in swallowing using voxel-based lesion symptom mapping (VLSM).

RESULTS

The group of patients who showed delayed oral transit time had significantly low cognitive function. Also, in a regression model, delayed oral phase was predicted with low K-MMSE (Korean version of the Mini Mental Status Exam). Using VLSM, we found the lesion location to be associated with delayed oral phase after adjusting for K-MMSE score. Although these results did not reach statistical significance, they showed the lesion pattern with predominant distribution in the left frontal lobe.

CONCLUSION

Delayed oral phase in post-stroke patients was not negligible clinically. Patients' cognitive impairments affect the oral transit time. When adjusting it, we found a trend that the lesion responsible for delayed oral phase was located in the left frontal lobe, though the association did not reach significance. The delay might be related to praxis function.

Functional changes of neural circuits in stroke patients with dysphagia: A meta-analysis

OBJECTIVE

Dysphagia is a common problem in stroke patients with unclear pathogenesis. Several recent functional magnetic resonance imaging (fMRI) studies had been carried out to explore the cerebral functional changes in dysphagic stroke patients. The aim of this study was to analysis these imaging findings using a meta-analysis.

METHODS

We used seed-based d mapping (SDM) to conduct a meta-analysis for dysphagic stroke patients prior to any kind of special treatment for dysphagia. A systematic search was conducted for the relevant studies. SDM meta-analysis method was used to examine regions of increased and decreased functional activation between dysphagic stroke patients and healthy controls.

RESULTS

Finally, six studies including 81 stroke patients with dysphagia and 78 healthy controls met the inclusion standards. When compared with healthy controls, stroke patients with dysphagia showed hyperactivation in left cingulate gyrus, left precentral gyrus and right posterior cingulate gyrus, and hypoactivation in right cuneus and left middle frontal gyrus.

CONCLUSIONS

The hyperactivity of precentral gyrus is crucial in stroke patients with dysphagia and may be associated with the severity of stroke. Besides the motor areas, the default-mode network regions (DMN) and affective network regions (AN) circuits are also involved in dysphagia after stroke.

Effect of transcranial direct current stimulation on swallowing apraxia and cortical excitability in stroke patients

BACKGROUND

Swallowing apraxia is characterized by impaired volitional swallowing but relatively preserved reflexive swallowing. Few studies are available on the effectiveness of behavioral therapy and management of the condition.

OBJECTIVE

This study aimed to investigate the effect of transcranial direct current stimulation (tDCS) on swallowing apraxia and cortical activation in stroke patients.

METHODS

The study included three inpatients (age 48-70 years; 1 male, 2 females; duration of stroke, 35-55 d) with post-stroke swallowing apraxia and six age-matched healthy subjects (age 45-65 years; 3 males, 3 females). Treatments were divided into two phases: Phase A and Phase B. During Phase A, the inpatients received three weeks of sham tDCS and conventional treatments. During Phase B, these patients received three weeks of anodal tDCS over the bilateral primary sensorimotor cortex (S₁M₁) of swallowing and conventional treatments. Swallowing apraxia assessments were measured in three inpatients before Phase A, before Phase B, and after Phase B. The electroencephalography (EEG) nonlinear index of approximate entropy (ApEn) was calculated for three patients and six healthy subjects.

RESULTS

After tDCS, scores of swallowing apraxia assessments increased, and ApEn indices increased in both stimulated and non-stimulated areas.

CONCLUSIONS

Anodal tDCS might provide a useful means for recovering swallowing apraxia, and the recovery could be related to increased excitability of the swallowing cortex. Further investigations should explore the relationship between lesion size and/or lesion site and the prognosis of swallowing apraxia. Clinical trial registry: http://www.chictr.org Registration Number: ChiCTR-TRC-14004955.

Spatiotemporal characteristics of the pharyngeal event-related potential in healthy subjects and older patients with oropharyngeal dysfunction

BACKGROUND

Oropharyngeal dysphagia (OD) is a highly prevalent symptom in older people. Appropriate oropharyngeal sensory feedback is essential for safe and efficient swallowing. However, pharyngeal sensitivity decreases with advancing age and could play a fundamental role in the physiopathology of swallowing dysfunction associated with aging. We aimed to characterize pharyngeal sensitivity and cortical response to a pharyngeal electrical stimulus in healthy volunteers (HV) and older patients with and without OD.

METHODS

Eight young HV, eight older HV without OD, and 14 older patients with OD were studied by electroencephalography through 32 scalp electrodes. Pharyngeal event-related potentials (ERP) were assessed following electrical stimulation of the pharynx. Sensory and tolerance thresholds to the electrical stimulus and latency, amplitude, and scalp current density of each ERP component were analyzed and compared. An ERP source localization study was also performed using the sLORETA software.

KEY RESULTS

Older participants (with and without OD) presented an increased sensory threshold to pharyngeal electrical stimulation (10.2 ± 1.7 mA and 11.5 ± 1.9 mA respectively), compared with young HV (6.0 ± 1.2 mA). The cortical activation of older HV in response to pharyngeal electrical stimulus was reduced compared with young HV (N2 amplitude: 0.22 ± 0.79 vs -3.10 ± 0.59, P<.05). Older patients with OD also presented disturbances to the pharyngo-cortical connection together with disrupted pattern of cortical activation.

CONCLUSIONS AND INFERENCES

Older people present a decline in pharyngeal sensory function, more severe in older patients with OD. This sensory impairment might be a critical pathophysiological element and a potential target for treatment of swallowing dysfunction in older patients.

Diverging lesion and connectivity patterns influence early and late swallowing recovery after hemispheric stroke

Knowledge about the recovery of oral intake after hemispheric stroke is important to guide therapeutic decisions, including the administration of enteral tube feeding and the choice of the appropriate feeding route. They aimed to determine the localization and connectivity of lesions in impaired recovery versus recovered swallowing after initially dysphagic stroke. Sixty-two acute ischemic hemispheric stroke patients with impaired oral intake were included in a prospective observational cohort study. Voxel-based lesion-symptom mapping and probabilistic tractography were used to determine the association of lesion location and connectivity with impaired recovery of oral intake ≥7 days (indication for early tube feeding) and ≥4 weeks (indication for percutaneous endoscopic gastrostomy feeding) after stroke. Two distinct patterns influencing recovery of swallowing were recognized. Firstly, impaired recovery of oral intake after ≥7 days was significantly associated with lesions of the superior corona radiata (65% of statistical map, P < 0.05). The affected fibers were connected with the thalamus, primary motor, and supplemental motor areas and the basal ganglia. Secondly, impaired recovery of oral intake after ≥4 weeks significantly correlated with lesions of the anterior insula (54% of statistical map, P < 0.05), which was connected to adjacent operculo-insular areas of deglutition. These findings indicate that early swallowing recovery is influenced by white matter lesions disrupting thalamic and corticobulbar projection fibers. Late recovery is determined by specific cortical lesions affecting association fibers. This knowledge may help clinicians to identify patients at risk of prolonged swallowing problems that would benefit from enteral tube feeding. Hum Brain Mapp 38:2165-2176, 2017. © 2017 Wiley Periodicals, Inc.

Brain regions involved in swallowing: Evidence from stroke patients in a cross-sectional study

Background:

Limited data available about the mechanisms of dysphagia and areas involving swallow after brain damage; accordingly it is hard to predict which cases are more likely to develop swallowing dysfunction based on the neuroimaging. The aim of this study was to investigate the relationship between brain lesions and dysphagia in a sample of acute conscious stroke patients.

Materials and Methods:

In a cross-sectional study, 113 acute conscious stroke patients (69 male mean [standard deviation (SD)] age 64.37 [15.1]), participated in this study. Two neurologists and one radiologist localized brain lesions according to neuroimaging of the patients. Swallowing functions were assessed clinically by an expert speech pathologist with the Mann Assessment of Swallowing Ability (MASA). The association of brain region and swallowing problem was statistically evaluated using Chi-square test.

Results:

Mean (SD) MASA score for the dysphagic patients was 139.61 (29.77). Swallowing problem was significantly more prevalent in the right primary sensory (P = 0.03), right insula (P = 0.005), and right internal capsule (P = 0.05).

Conclusion:

It may be concluded from these findings that the right hemisphere lesions associated with occurring dysphagia. Further studies using more advanced diagnostic tools on big samples particularly in a perspective structure are needed.

Differential response properties of peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats

We compared onset latency, motor-response patterns, and the effect of electrical stimulation of the cortical masticatory area between peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats. The number of swallows and the motor patterns were determined using electromyographic recordings from the thyrohyoid, digastric, and masseter muscles. The onset latency of the first swallow evoked by electrical stimulation of the cortical swallowing area (Cx) was significantly longer than that evoked by stimulation of the superior laryngeal nerve (SLN). The duration of thyrohyoid burst activity associated with SLN-evoked swallows was significantly longer than that associated with either Cx-evoked or spontaneous swallows. Combining Cx with SLN stimulation increased the number of swallows at low levels of SLN stimulation. Finally, A-area (the orofacial motor cortex) stimulation inhibited Cx-evoked swallows significantly more than it inhibited SLN-evoked swallows. These findings suggest that peripherally and cortically evoked swallows have different response properties and are affected differently by the mastication network.

Effects of non-invasive brain stimulation on post-stroke dysphagia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

The primary aim of this review is to evaluate the effects of non-invasive brain stimulation on post-stroke dysphagia.

METHODS

Thirteen databases were systematically searched through July 2014. Studies had to meet pre-specified inclusion and exclusion criteria. Each study's methodological quality was examined. Effect sizes were calculated from extracted data and combined for an overall summary statistic.

RESULTS

Eight randomized controlled trials were included. These trials revealed a significant, moderate pooled effect size (0.55; 95% CI=0.17, 0.93; p=0.004). Studies stimulating the affected hemisphere had a combined effect size of 0.46 (95% CI=-0.18, 1.11; p=0.16); studies stimulating the unaffected hemisphere had a combined effect size of 0.65 (95% CI=0.14, 1.16; p=0.01). At long-term follow up, three studies demonstrated a large but non-significant pooled effect size (0.81, p=0.11).

CONCLUSIONS

This review found evidence for the efficacy of non-invasive brain stimulation on post-stroke dysphagia. A significant effect size resulted when stimulating the unaffected rather than the affected hemisphere. This finding is in agreement with previous studies implicating the plasticity of cortical neurons in the unaffected hemisphere.

SIGNIFICANCE

Non-invasive brain stimulation appears to assist cortical reorganization in post-stroke dysphagia but emerging factors highlight the need for more data.

Voluntary Modulation of Hemodynamic Responses in Swallowing Related Motor Areas: A Near-Infrared Spectroscopy-Based Neurofeedback Study

In the present study, we show for the first time that motor imagery of swallowing, which is defined as the mental imagination of a specific motor act without overt movements by muscular activity, can be successfully used as mental strategy in a neurofeedback training paradigm. Furthermore, we demonstrate its effects on cortical correlates of swallowing function. Therefore, N = 20 healthy young adults were trained to voluntarily increase their hemodynamic response in swallowing related brain areas as assessed with near-infrared spectroscopy (NIRS). During seven training sessions, participants received either feedback of concentration changes in oxygenated hemoglobin (oxy-Hb group, N = 10) or deoxygenated hemoglobin (deoxy-Hb group, N = 10) over the inferior frontal gyrus (IFG) during motor imagery of swallowing. Before and after the training, we assessed cortical activation patterns during motor execution and imagery of swallowing. The deoxy-Hb group was able to voluntarily increase deoxy-Hb over the IFG during imagery of swallowing. Furthermore, swallowing related cortical activation patterns were more pronounced during motor execution and imagery after the training compared to the pre-test, indicating cortical reorganization due to neurofeedback training. The oxy-Hb group could neither control oxy-Hb during neurofeedback training nor showed any cortical changes. Hence, successful modulation of deoxy-Hb over swallowing related brain areas led to cortical reorganization and might be useful for future treatments of swallowing dysfunction.

Hemodynamic Signal Changes Accompanying Execution and Imagery of Swallowing in Patients with Dysphagia: A Multiple Single-Case Near-Infrared Spectroscopy Study

In the present multiple case study, we examined hemodynamic changes in the brain in response to motor execution (ME) and motor imagery (MI) of swallowing in dysphagia patients compared to healthy matched controls using near-infrared spectroscopy (NIRS). Two stroke patients with cerebral lesions in the right hemisphere, two stroke patients with lesions in the brainstem, and two neurologically healthy control subjects actively swallowed saliva (ME) and mentally imagined to swallow saliva (MI) in a randomized order while changes in concentration of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) were assessed. In line with recent findings in healthy young adults, MI and ME of swallowing led to the strongest NIRS signal change in the inferior frontal gyrus in stroke patients as well as in healthy elderly. We found differences in the topographical distribution and time course of the hemodynamic response in dependence on lesion location. Dysphagia patients with lesions in the brainstem showed bilateral hemodynamic signal changes in the inferior frontal gyrus during active swallowing comparable to healthy controls. In contrast, dysphagia patients with cerebral lesions in the right hemisphere showed more unilateral activation patterns during swallowing. Furthermore, patients with cerebral lesions showed a prolonged time course of the hemodynamic response during MI and ME of swallowing compared to healthy controls and patients with brainstem lesions. Brain activation patterns associated with ME and MI of swallowing were largely comparable, especially for changes in deoxy-Hb. Hence, the present results provide new evidence regarding timing and topographical distribution of the hemodynamic response during ME and MI of swallowing in dysphagia patients and may have practical impact on future dysphagia treatment.

Task-concurrent anodal tDCS modulates bilateral plasticity in the human suprahyoid motor cortex

Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability in humans. Here, we examined the effects of anodal tDCS on suprahyoid motor evoked potentials (MEP) when applied over the hemisphere with stronger and weaker suprahyoid/submental projections, respectively, while study participants performed a swallowing task. Thirty healthy volunteers were invited to two experimental sessions and randomly assigned to one of two different groups. While in the first group stimulation was targeted over the hemisphere with stronger suprahyoid projections, the second group received stimulation over the weaker suprahyoid projections. tDCS was applied either as anodal or sham stimulation in a random cross-over design. Suprahyoid MEPs were assessed immediately before intervention, as well as 5, 30, 60, and 90 min after discontinuation of stimulation from both the stimulated and non-stimulated contralateral hemisphere. We found that anodal tDCS (a-tDCS) had long-lasting effects on suprahyoid MEPs on the stimulated side in both groups (tDCS targeting the stronger projections: F_(1,14) = 96.2, p < 0.001; tDCS targeting the weaker projections: F_(1,14) = 37.45, p < 0.001). While MEPs did not increase when elicited from the non-targeted hemisphere after stimulation of the stronger projections (F_(1,14) = 0.69, p = 0.42), we found increased MEPs elicited from the non-targeted hemisphere after stimulating the weaker projections (at time points 30–90 min) (F_(1,14) = 18.26, p = 0.001). We conclude that anodal tDCS has differential effects on suprahyoid MEPs elicited from the targeted and non-targeted hemisphere depending on the site of stimulation. This finding may be important for the application of a-tDCS in patients with dysphagia, for example after stroke.