Oral and pharyngeal reflexes in the mammalian nervous system: their diverse range in complexity and the pivotal role of the tongue

Neurophysiology of swallowing: effects of age and bolus type

This study examined age-related changes in swallowing from an integrated biomechanical and functional imaging perspective in order to more comprehensively characterize changes in swallowing associated with age. We examined swallowing-related fMRI brain activity and videoflouroscopic biomechanics of three bolus types (saliva, water and barium) in 12 young and 11 older adults. We found that age-related neurophysiological changes in swallowing are evident. The group of older adults recruited more cortical regions than young adults, including the pericentral gyri and inferior frontal gyrus pars opercularis and pars triangularis (primarily right-sided). Saliva swallows elicited significantly higher BOLD responses in regions important for swallowing compared to water and barium. In separate videofluoroscopy sessions, we obtained durational measures of supine swallowing. The older cohort had significantly longer delays before the onset of the pharyngeal swallow response and increased residue of ingested material in the pharynx. These findings suggest that older adults without neurological insult elicit more cortical involvement to complete the same swallowing tasks as younger adults.

Somatosensory-evoked magnetic fields in examining lip area in speech-disordered children

Magnetoencephalography (MEG) is a modern neurophysiological method to study brain activation after sensory stimulation. We aimed at determining the feasibility of MEG and somatosensory-evoked magnetic fields (SEFs) in assessing the lip area in speech-disordered children undergoing oral plate therapy (OPTH) to improve their articulation. Seven subjects (age range, 6-11 years) participated in the study. The speech was perceptually assessed, and the SEFs to tactile stimulation of the lip area were recorded before and after OPTH. Two patients did not attend the posttreatment MEG recording. Clinical perceptual analysis showed remarkable improvement of speech of the studied children after OPTH. Somatosensory-evoked magnetic fields were successfully recorded in 4 of these children, but no constant changes in the responses were found after the therapy.With this small number of patients, the possible modifications in the functioning of the cortical somatosensory area of the lip after OPTH remained undetected. The present method is, however, technically applicable in studying cortical responses to lip stimulation in speech-disordered children. Further studies using stimulation inside the mouth may provide more insight to the cortical effects of OPTH.

Combined videofluoroscopy and manometry in the diagnosis of oropharyngeal dysphagia: examination technique and preliminary experience

PURPOSE

Dysphagia is a symptom of different pathological conditions characterised by alteration of the swallowing mechanism, which may manifest at different levels. We report our experience in the evaluation of the swallowing mechanism with combined videofluoroscopy and manometric recordings.

MATERIALS AND METHODS

For the combined study, we used a Dyno Compact computerised system (Menfis Biomedical s.r.l., Bologna, Italy) equipped with: (1) graphics card for the management of ultrasonographic or radiological images; (2) A.VI.U.S. dedicated software package, which enables digital-quality recording (PAL/NTSC, composite video or S-Video) of the videofluoroscopy study in AVI format with 320 x 240 resolution and 25 Hz acquisition frequency. The delay introduced by the process of image digitalisation is in the order of 200 ms, so for analysis purposes, the images can be considered synchronised with the manometric recordings. The videomanometry study was performed with the administration of contrast material either in bolus form or diluted. Data were collected on a specifically designed grid for the evaluation of 46 videofluoroscopic items, of which 34 are derived from the laterolateral view (seven in the oral preparatory phase, 15 in the oral transport phase and 12 in the pharyngeal phase) and 12 in the anteroposterior view (six in the oral preparatory phase and six in the oropharyngeal phase). A positive finding for the individual parameters is expressed in a binary fashion. Manometric evaluation was based on 11 items divided into four major and seven minor criteria.

RESULTS

Dynamic videofluoroscopy swallow study combined with concurrent manometry enabled the simultaneous recording of anatomical alterations and the functional data of oropharyngeal pressure, thus providing a picture of the anatomical, biomechanical and physiological conditions of swallowing and the manner of bolus propulsion and transit.

CONCLUSIONS

An early and effective diagnosis of oropharyngeal dysphagia means being able to effectively implement appropriate rehabilitation techniques, improve the patient's quality of life, and minimise the complications associated with swallowing disorders (choking, aspiration pneumonia, malnourishment). Distinction of the anatomical level of dysphagia is not a matter of simple classification; rather, it is essential in that different clinical presentations require different diagnostic strategies, and a precise definition of the anatomical-functional substrate is required to implement the correct therapeutic approach. This study presents the authors' experience with the use of combined videofluoroscopy and manometry with particular emphasis on the examination technique.

Manual stimulation of the suprahyoid-sublingual region diminishes polynnervation of the motor endplates and improves recovery of function after hypoglossal nerve injury in rats

BACKGROUND

Using the rat facial nerve axotomy model, the authors recently showed that manual stimulation of denervated whiskerpad muscles reduced the posttransectional polyinnervation at the neuromuscular junctions and promoted full recovery of vibrissal whisking.

OBJECTIVE

Prompted by implications for rehabilitation therapy, the authors examined whether manual stimulation of denervated supra- and infrahyoid muscles would also improve recovery after unilateral lesion on the hypoglossal nerve.

METHODS

Adult rats underwent transection of the right hypoglossal nerve. Half of the animals received no postoperative treatment, and the other half were subjected to daily manual stimulation of the suprahyoid/sublingual region for 2 months. Recovery was assessed by measuring the angle of tongue-tip deviation from the midline, degree of collateral axonal branching at the lesion site (counts after retrograde labeling with 2 fluorescent dyes), synaptic input to the hypoglossal motoneurons using synaptophysin immunocytochemistry, tongue-muscles motor representation in the cerebral cortex after c-Fos immunocytochemistry, and portion of polyinnervated neuromuscular junctions.

RESULTS

In animals receiving manual stimulation, the tongue-tip deviation was 37.0 +/- 49.37 degrees , whereas values in control nonstimulated rats were significantly higher (50.1 +/- 9.01 degrees ; P < .05; mean +/- SD). Improved recovery was not associated with reduced collateral axonal branching; there were also no differences in tongue-muscles representation in the motor cortex. However, manual stimulation restored the total synaptic input to levels in intact animals and reduced the proportion of polyinnervated neuromuscular junctions compared with nonstimulated animals.

CONCLUSION

The data show that manual stimulation of denervated muscles improves functional outcome following peripheral nerve injury. This suggests immediate potential for enhancing clinical rehabilitation strategies.

Tongue movement and intra-oral vacuum in breastfeeding infants

OBJECTIVE

The mechanism by which the breastfeeding infant removes milk from the breast is still controversial. It is unclear whether the infant uses predominantly intra-oral vacuum or a peristaltic action of the tongue to remove milk from the breast. The aim of this study was to use ultrasound to observe movements of the tongue during breastfeeding and relate these movements to both milk flow and simultaneous measurements of intra-oral vacuum.

METHODS

Submental ultrasound scans of the oral cavity of 20 breastfed infants (3-24 weeks old) were performed during a breastfeed. Intra-oral vacuums were measured simultaneously via a milk-filled supply line (SNS) connected to a pressure transducer.

RESULTS

Vacuum increased during the downward motion of the posterior tongue and at the same time milk flow and milk ducts in the nipple was observed. Peak vacuum (-145+/-58 mmHg) occurred when the tongue was in the lowest position.

CONCLUSIONS

Ultrasound imaging demonstrated that milk flow from the nipple into the infant's oral cavity coincided with both the lowering of the infants tongue and peak vacuum. Therefore vacuum is likely to play a major role in milk removal from the breast.

Reabilitação em disfagia orofaríngea neurogênica: sabor azedo e temperatura fria

TEMA: reabilitação em disfagia orofaríngea neurogênica OBJETIVO: apresentar revisão de literatura sobre os controles neurofisiológicos da deglutição orofaríngea e a influência do sabor azedo e da temperatura fria no mecanismo da deglutição. CONCLUSÃO: quanto à questão do controle central da deglutição, ainda existem controvérsias em relação ao sabor azedo e a temperatura fria. Esses dois parâmetros provocam mudanças na dinâmica da deglutição, podendo trazer benefícios aos indivíduos acometidos por disfagia orofaríngea neurogênica. Porém, tais achados sugerem a necessidade de investigações futuras com populações randomizadas.

Estimulação mecânico-térmica dos pilares palatoglosso

RACIONAL: Os pilares palatoglosso foram admitidos como a principal sede dos receptores responsáveis por iniciar a fase faríngea da deglutição. Essa fase reflexa iniciar-se-ia em resposta ao estímulo produzido pelo progresso do bolo e da língua em sentido posterior. Esses conceitos deram base à manobra mecânico-térmica que visa estimular os receptores desses pilares, produzindo respostas motoras capazes de potencializar a recuperação da função faríngea comprometida. O conceito de possível resposta motora ao estímulo desses pilares, embora comum, não é unanimemente aceito. OBJETIVO: Verificar as possíveis respostas motoras produzidas pelo estímulo mecânico- térmico sobre os pilares palatoglosso. MÉTODOS: Por entender que indivíduos sadios são capazes de prover respostas reflexas mais efetivas do que as que seriam obtidas em pacientes, avaliaram-se 51 voluntários adultos sadios de ambos os sexos reproduzindo o estímulo sobre os pilares, usando sonda metálica de ponta romba resfriada em água mantida a 10°C. RESULTADOS E CONSIDERAÇÕES: O estudo mostrou que o estímulo mecânico-térmico sobre os pilares não foi capaz de produzir qualquer resposta motora envolvida na dinâmica da fase faríngea da deglutição. É possível que as respostas contráteis observadas em alguns estudos devam-se ao reflexo de gag inadequadamente interpretado ou a contrações voluntárias inconscientes por esforço de manutenção da abertura da boca e externalização da língua durante a exposição dos pilares para execução da manobra de estimulação mecânico-térmica.

Effect of aging on tongue protrusion forces in rats

The purpose of this study was to ascertain the effect of aging on muscle contractile properties associated with tongue protrusion in a rat model. Fischer 344/Brown Norway hybrid rats, ten young (9 months old) and ten old (32 months old), were used to measure protrusive contractile properties. Results showed a significant reduction in tetanic forces in the old animals. The following measures of muscle contraction were not different between age groups: mean twitch contraction force, twitch contraction time, twitch contraction half-decay time, and a calculated measure of fatigability. In conclusion, aging influenced protrusive tongue muscle contractions in a rat model such that tetanic forces were reduced. The reduction of tetanus force may parallel findings in human subjects relative to isometric tongue force generation and may be associated with age-related disorders of swallowing.

Biochemistry of anterior, medial, and posterior genioglossus muscle in the rat

The tongue plays a vital role in swallowing actions. However, tongue muscles have been understudied, and it is unclear if tongue muscles are homogeneous with respect to muscle fiber-type distribution. We examined myosin heavy chain (MHC) composition of anterior, medial, and posterior sections of the genioglossus muscle (GG) using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in ten adult (9 months old) male Fischer 344/Brown Norway hybrid rats. We found that Type IIx MHC predominated in the anterior, medial, and posterior regions of the GG muscle (p=0.002), followed by IIa, then IIb. The anterior GG contained a significantly greater (p=0.004) proportion of Type IIa than did the medial or posterior regions, while the posterior GG contained a significantly greater (p=0.002) proportion of Type IIb MHC than did the medial or anterior GG. Accordingly, we found variable expression of MHC isoforms across anterior, medial, and posterior portions of the GG muscle, with more fast-contracting isoforms found posteriorly. Because motor control of the tongue requires precise and rapid movements for bolus manipulation and airway protection, variable expression of MHC isoforms along the anteroposterior axis of the GG muscle may be required to efficiently achieve deglutition and maintenance of airway patency.

Neuronal circuitry and synaptic organization of trigeminal proprioceptive afferents mediating tongue movement and jaw-tongue coordination via hypoglossal premotor neurons

The neural framework and synaptic organization of trigeminal proprioceptive afferent-mediated jaw-tongue coordination were studied in rats using multiple electrophysiological and neuroanatomical approaches. Electrostimulation of the masseter nerve evoked short-latency responses (5.86 +/- 2.59 ms) in hypoglossal premotor pools including the parvocellular (PCRt) and intermediate (IRt) reticular nuclei and the dorsomedial part of the spinal trigeminal nucleus oralis (Vodm) and interpolaris (Vidm). Biocytin-labelled axon terminals from these areas traveled into the hypoglossal nucleus (XII) and contacted motoneurons. Double labelling of biotinylated dextran amine (BDA) tracing and cholera toxin B (CTB) transport demonstrated that labelled axons and terminals from the mesencephalic trigeminal nucleus (Vme) overlapped with XII premotor neurons in the alpha division and in PCRt, IRt, Vodm and Vidm. Confocal microscopic observations revealed that Vme terminals closely contacted XII premotor neurons. Dual labelling of intracellular neurobiotin staining of jaw-muscle spindle afferents (JMSAs) combined with horseradish peroxidase (HRP) retrograde transport revealed that 498 JMSA boutons apposed to 146 HRP-labelled premotor neurons. Electron microscopic observations demonstrated that 127 JMSA boutons made both axodendritic (68%) and axosomatic (32%) synapses with XII premotor neurons. Eighty-three per cent of synapses were asymmetric and the rest (17%) were symmetric. Thirty-nine per cent of JMSA boutons received presynaptic contacts from P-type terminals. Varieties of synaptic organizations were found. These results provide evidence that trigeminal proprioceptive afferents mediate jaw-tongue coordination through XII premotor neurons. Ultrastructural findings demonstrated that synapses between JMSA boutons and XII premotor neurons are predominantly excitatory, and synaptic transmission to XII motoneurons is modified on XII premotor neurons by presynaptic mechanisms. These frameworks and synaptic organizations are most probably the neural substrate for trigeminal proprioceptive afferent-mediated jaw-tongue coordination.

Anatomic study of tongue architecture based on fetal histological sections

Tongue muscles are difficult to study by dissection and imaging methods because of the intermeshing of the muscular fibers. The study of the architecture of the tongue was based on 853 tongue sections of a fetus aged 32 weeks after conception. The analysis of the sections allowed demonstration of the different intrinsic and extrinsic muscles of the tongue, to determine their situation from the palatoglossus arch to the apex of the tongue. The tongue muscles are organized in different layers from cranial to caudal and from lateral to medial, one medial for the genioglossus muscle, one paramedial for the hyoglossus, the styloglossus and the inferior longitudinal muscles. In the anterior third of the tongue, the muscles presented a concentric organization.

Modulation of upper airway muscle activities by bronchopulmonary afferents

Here we review the influence of bronchopulmonary receptors (slowly and rapidly adapting pulmonary stretch receptors, and pulmonary/bronchial C-fiber receptors) on respiratory-related motor output to upper airway muscles acting on the larynx, tongue, and hyoid arch. Review of the literature shows that all muscles in all three regions are profoundly inhibited by lung inflation, which excites slowly adapting pulmonary stretch receptors. This widespread coactivation includes the recruitment of muscles that have opposing mechanical actions, suggesting that the stiffness of upper airway muscles is highly regulated. A profound lack of information on the modulation of upper airway muscles by rapidly adapting receptors and bronchopulmonary C-fiber receptors prohibits formulation of a conclusive opinion as to their actions and underscores an urgent need for new studies in this area. The preponderance of the data support the view that discharge arising in slowly adapting pulmonary stretch receptors plays an important role in the initiation of the widespread and highly coordinated recruitment of laryngeal, tongue, and hyoid muscles during airway obstruction.

One hour of tongue-task training is associated with plasticity in corticomotor control of the human tongue musculature

Corticomotor control of the human tongue has been reported to undergo neuroplastic changes following several days of training in a tongue-protrusion task. The aims of the present study were to determine if a 1 h tongue-task training is sufficient to induce signs of neuroplastic changes in the corticomotor pathways, and to obtain preliminary information on the time course of such changes. Corticomotor excitability was assessed by changes in electromyographic activity evoked by transcortical magnetic stimulation (TMS) in 11 healthy subjects. Motor evoked potentials (MEPs) recorded in the tongue musculature and the first dorsal interosseous (FDI) muscle were assessed at four sessions: at baseline before training, 30 min after training, and 1 and 7 days after training. All subjects performed successfully the task (success rate: 38+/-4%). Thresholds for evoking MEPs by TMS in the tongue were decreased at 30 min, 1 and 7 days after training compared with baseline (ANOVA: P<0.001). Tongue MEP amplitudes were significantly increased at 1 day follow-up and had returned to baseline values at 7 days follow-up (ANOVA: P<0.001). No significant effect of tongue-task training on FDI MEPs was observed (ANOVA: P=0.160). Corticomotor topographic maps revealed increases (ANOVA: P<0.001) in area at the 1 day follow-up. The success rate was significantly correlated to the net increases in tongue MEPs at 1 day follow-up (Spearman: 0.615; P=0.0039). The present findings confirm that tongue task training is associated with plasticity of corticomotor excitability specifically related to the tongue musculature and further document that plasticity is evident within 30 min post-training and may last up to at least 7 days.

Quantitative analysis of surface EMG activity of cranial and leg muscles across sleep stages in human

OBJECTIVE

The aim of this study was to make a quantitative analysis of the changes in cranial and limb muscle activity from wakefulness to light and deep sleep stages and during rapid eye movement (REM) sleep of normal subjects.

METHODS

Polysomnographic recordings were made of the sleep of 9 healthy human subjects, including electromyograms of the suprahyoid, temporalis and masseter cranial muscles and the anterior tibialis limb muscle. Quantitative assessments of EMG activity were carried out with root mean square (RMS) and frequency-spectral analysis (FSA) methods.

RESULTS

From wakefulness to sleep, a significant reduction (-25.2 to -71.2%; P < 0.01) was observed in EMG activity (for both RMS and FSA) of the 3 cranial muscles using both methods of analysis. The EMG activity of suprahyoid muscle further decreased from non-REM to REM sleep (-17.8 to -43.0%; P < 0.01). In contrast, the EMG activity of the anterior tibialis muscle was only slightly reduced across sleep stages and did not further reduce during REM sleep. During REM sleep, all the 4 muscles maintained minimal activity.

CONCLUSIONS

The maintenance of muscle activity during REM sleep suggests that a minimal level of activity is required to preserve physiological functions (e.g. airway patency, posture) related to homeostasis and bodily protection.

SIGNIFICANCE

This study suggests that quantitative sleep EMG analysis is important for understanding the mechanisms of sleep-related movement disorders or when objective assessment of changes in EMG activity are needed for diagnostic purposes or for the assessment of drug efficiency.

Taste Disorders in Acute Stroke

Background and Purpose— The aim of the study was to assess whether and how frequently patients with acute first-ever stroke exhibit gustatory dysfunction.

Methods— We performed a 1-year prospective observational study. Gustatory function was assessed using the standardized “taste strips” test. In addition, we assessed olfactory function, swallowing, stroke location, comorbidities, and the patients’ medication.

Results— A total of 102 consecutive patients were enrolled (45 female, 57 male; mean age, 63 years); 31 of them (30%) exhibited gustatory loss and 7 (6%) had lateralized impairment of taste function. Predictors of impaired taste function were male gender ( P =0.003), high National Institutes of Health Stroke Scale (NIHSS) score at admission ( P =0.009), coexisting swallowing dysfunction ( P =0.026), and a stroke of partial anterior circulation subtype (PACS) ( P =0.008). In particular, in hypogeusic patients the lesion was most frequently localized in the frontal lobe ( P =0.009). Follow-up examinations in 14 patients indicated improvement of taste sensitivity.

Conclusion— Taste disorders after stroke are frequent. A significant association was found for male gender, high NIHSS score, swallowing disorder, and PACS, particularly in the frontal lobe. Generally, taste disorders after stroke seem to have a good prognosis.

Activation of XII motoneurons and premotor neurons during various oropharyngeal behaviors

Neural control of tongue muscles plays a crucial role in a broad range of oropharyngeal behaviors. Tongue movements must be rapidly and accurately adjusted in response to the demands of multiple complex motor tasks including licking/mastication, swallowing, vocalization, breathing and protective reflexes such as coughing. Yet, central mechanisms responsible for motor and premotor control of hypoglossal (XII) activity during these behaviors are still largely unknown. The aim of this article is to review the functional organization of the XII motor nucleus with particular emphasis on breathing, coughing and swallowing. Anatomical localization of XII premotor neurons is also considered. We discuss results concerned with multifunctional activity of medullary and pontine populations of XII premotor neurons, representing a single network that can be reconfigured to produce different oromotor response patterns. In this context, we introduce new data on swallowing-related activity of XII (and trigeminal) motoneurons, and finally suggest a prominent role for the pontine Kölliker-Fuse nucleus in the control of inspiratory-related activity of XII motoneurons supplying tongue protrusor and retrusor muscles.

The uniqueness of speech among motor systems

This paper considers evidence that the speech muscles are unique in their genetic, developmental, functional and phenotypical properties. The literature was reviewed using PubMed, ScienceDirect, ComDisDome and other literature-retrieval systems to identify studies reporting on the craniofacial and laryngeal muscles. Particular emphasis was given to studies of muscle fibre composition. A number of studies on mandibular, lingual, palatal and laryngeal muscles in humans show that these muscles are distinct from limb and other muscles. These speech-related muscles typically contain diverse fibre types and these types can vary regionally within a muscle. In general, the muscles of the speech production system are designed for fast and/or variable contraction and fatigue resistance. The craniofacial and laryngeal muscles are unique among the muscle systems of the human body and the specialized properties of these muscles are relevant to understanding the biomechanics of speech and various speech disorders.

Asymmetric Tongue Muscle Uptake of F-18 FDG

A 58-year-old woman, with nonsmall cell carcinoma, had multiple metastasis on 2-F-18 FDG positron emission tomography imaging. The right hemitongue had increased activity as compared with the left. This was not the result of the presence of a metastasis to the tongue, as shown by a negative computed tomography scan of the region and failure to demonstrate a lesion over a period of weeks. Uptake was likely related to right hemiglossal muscle activity. This was made more apparent by decreased uptake on the opposite side of the tongue (up to the midline) as a result of left cranial nerve XII paralysis.