Orofacial Muscles Research Articles

Tongue contractions during speech may have led to the development of the bony geometry of the chin following the evolution of human language: A mechanobiological hypothesis for the development of the human chin

One of the most fundamental yet unanswered questions of human evolution is that of the development of the chin. Whereas it is known that the chin, or mentum osseum, is an unique anatomical feature of modern humans that emerged during the Middle and Late Pleistocene, its origin and biomechanical significance are the subjects of intense controversy. Theories range from the suggestion that the chin evolved as a result of progressive reduction of the dental arch, which left it as a protrusion, to the hypothesis that it provided resistance to mandibular bending during mastication. Until now however, no accepted functional explanation of the human chin has emerged. Here, we develop the hypothesis that the actions of the tongue and non-masticatory orofacial muscles may have played a significant role on the development of the human chin. We report numerical simulations of the forces and resultant stresses developed in hypothetical chinned and non-chinned mandibles. Using empirical data and estimates of the forces generated by the human tongue during speech, our hypothesis suggests that the chin might in fact have developed as a result of the actions of the tongue and perioral muscles, rather than as a buttress to withstand masticatory induced stress. This provides a new perspective on the generation of the chin and importantly, suggests that its appearance may be causally related to the development of the human language.

The effect of mastication muscular tone on facial size in patients with Down syndrome

Muscular hypotonia is one of the clinical signs in patients with Down syndrome. As a characteristic of patients with Down syndrome, hypotonia is clearly evident in face expression and oral dysfunction. Dentocraniofacial growth abnormalities in patients with Down syndrome may be influenced by genetic and environmental factors. Stomatognathic system musculature as an environmental factor (factor outside the bone) can affect dentocraniofacial growth by orofacial muscles activities when chewing, swallowing, breathing, and speaking. Oral dysfunctions commonly seen in patients with Down syndrome are open mouth, protruding tongue posture, difficulties when chewing, swallowing, and speaking, drooling, and mouth breathing. The purpose of this study was to observe how the mastication muscular tone affecting the facial size of Down syndrome patient. Twenty five of 14–18 years old children with Down syndrome were diagnosed by clinical characteristic and cytogenetic examination. Mastication muscular tone was described by masseter and temporalis muscle synergy and oral function, whereas the facial size consisted of facial size of lateral, anteroposterior and vertical growth. The result of regression test revealed that the degree of mastication muscular tone has a significant effect on facial size of the anteroposterior growth and facial size of vertical growth, but did not significantly influence the facial size of lateral growth.

What Is Orofacial Fatigue and How Does It Affect Function for Swallowing and Speech?

Speech-language pathologists are likely to encounter patients who report symptoms of fatigue, but there are few clinical procedures to assess this phenomenon. Furthermore, it is difficult to determine whether fatigue contributes to a patient's dysphagia or dysarthria. This article reviews orofacial muscles, including the muscles of the tongue, lips, and cheeks, highlighting in particular their role in swallowing and speaking. It provides definitions of fatigue and describes assessment procedures. The author's research has focused on assessing fatigue, especially of the tongue, and elucidating the effects of exercising the tongue on speech and nonspeech tasks. Most of this work involves people who have Parkinson's disease and neurologically normal adults; results generally support heightened fatigue in Parkinson's disease. However, the effect of fatigue on functional activities remains unclear. Literature regarding the effects of orofacial fatigue on swallowing and speaking is notably sparse, but preliminary evidence indicates that these functions are rather robust.

Orofacial Muscle Pain: New Advances in Concept and Therapy

This manuscript focuses on chronic myogenous pains affecting the masticatory muscles. The differentiation of myogenous masticatory pain into subcategories is proposed by separating myogenous pains according to their location and anatomic extent. Focal myalgia, regional myalgia, myofascial pain, and fibromyalgia are classified based on specific historical and clinical examination criteria. The probable mechanisms underlying chronic myogenous pains and trigger points phenomena are discussed. Treatment options of the myogenous masticatory pain conditions including physical medicine modalities, as well as several types of pharmacologic agents, are presented.

Myosin heavy chain expression and muscle adaptation to chronic oral breathing in rat

The purpose of this study was to establish if early chronic oral breathing could induce an ultra-structural adaptation of the diaphragm and orofacial muscles related to oral or nasal breathing. Therefore, we performed a bilateral nasal obstruction at day 8 on rat pups and the myosin heavy chain (MHC) composition of the muscles was analyzed at day 21. Nasal obstruction and the related switch to chronic oral breathing were associated with impaired growth, atrophy of olfactory bulbs, hypertrophy of adrenal glands and reduced muscle growth for all muscles studied except the diaphragm. Furthermore, we detected a smaller decrease of MHC 2b compared to MHC 2a and 2x in levator nasolabialis, a muscle involved with nasal breathing. In masseter superficialis and anterior digastric involved with oral breathing, we observed a smaller decrease of MHC 2a compared to MHC 2b or 2x, respectively. No difference was detected in the diaphragm MHC expression of oral breathing animals. Since the relative expression of fatigue resistant MHC fiber types increased in muscles involved with oral breathing, orofacial muscles seem to present a profile in MHC adapted to the transition from nasal to oral breathing, facilitating respiration.

Strategies for block-design fMRI experiments during task-related motion of structures of the oral cavity

Functional MRI (fMRI) studies of jaw motion, speech, and swallowing disorders have been hampered by motion artifacts. Tissue motion perturbs the static magnetic field, creating geometric distortions in echo-planar images that lead to many false positives in activation maps. These problems have restricted blood oxygenation level-dependent (BOLD) fMRI studies involving orofacial muscles to event-related designs, which offer weak contrast-to-noise ratios when compared to block designs. Two new approaches are described that greatly reduce false positives in the activation maps created by the distortions in block-design fMRI studies involving jaw and tongue motion during chewing. First, an appropriate task duration of 10−14 s was found to maximize functional contrast while minimizing motion artifacts. Second, three motion-sensitive postprocessing methods were applied successively to examine the temporal and spatial characteristics of responses and identify and remove false positives caused by motion artifacts. These techniques are shown to allow the use of block design in an fMRI study of a jaw motion task. Extension to speech and swallowing tasks is discussed.

Chewing Indicators between Adults with Down Syndrome and Controls

Down syndrome induces a neuromotor deficiency that affects the orofacial musculature, and thus could be implicated in the feeding difficulties affecting people with this disease. This study aimed to investigate the differences in chewing indicators between a group of 11 adults with Down syndrome and a group of 12 healthy subjects without Down syndrome. Chewing ability was evaluated by means of video recordings taken during a standardized meal that included 10 natural foods. The variables collected were masticatory time, number of masticatory cycles, chewing frequency, number of open masticatory cycles, and number of food refusals. There were several differences in both directions for masticatory time and number of masticatory cycles between the two groups. In addition, with the exception of purée, the group with Down syndrome had significantly lower mean chewing frequency than the reference group, and was unable to eat all the foods presented.

Orofacial somatomotor responses in the macaque monkey homologue of Broca's area

In the ventrolateral frontal lobe of the human brain there is a distinct entity, cytoarchitectonic area 44 (Broca's area), which is crucial in speech production. There has been controversy over whether monkeys possess an area comparable to human area 44. We have addressed this question in the macaque monkey by combining quantitative architectonic analysis of the cortical areas within the ventrolateral frontal region with electrophysiological recording of neuron activity and electrical intracortical microstimulation. Here we show that, immediately in front of the ventral part of the agranular premotor cortical area 6, there is a distinct cortical area that is architectonically comparable to human area 44 and that this monkey area 44 is involved with the orofacial musculature. We suggest that area 44 might have evolved originally as an area exercising high-level control over orofacial actions, including those related to communicative acts, and that, in the human brain, area 44 eventually also came to control certain aspects of the speech act.

Clinical Decision Making and Oral Motor Treatments

Clinical Decision Making and Oral Motor Treatments

Quantification of MyHC mRNA in masticatory muscles during orthodontic treatment in pigs

Orthodontic treatment of retrognathism is aimed at correcting the position of the jaws and at rectifying functional problems. Changes induced in the bone morphology of the mandible and in the dentoalveolar region by different appliances are well documented. Less is known and measurable with respect to the functional status and muscular capacity of orofacial muscles induced by the appliance within the framework of the training effect in Class II malocclusion cases. The aim of the present investigation was to analyze and quantify the change in fiber type levels of type I (slow Myosin heavy chain (MyHC)) and type IIb (fast b MyHC) MyHC RNA transcripts, using the competitive reverse polymerase chain reaction (cRT-PCR) during sagittal advancement of the mandible in pigs. The experiments were carried out on 10-week-old piglets (six test animals, six controls) over a period of 28 days. Six piglets received acrylic build-ups for permanent sagittal advancement of the mandible. Muscle tissue was taken from seven different regions of the masseter (m1-3), temporal (tp1, 2), medial pterygoid (pm), and geniohyoid muscles (gh). A marked increase in the absolute amount of slow MyHC RNA transcripts was detected after treatment in the anterior region and in the medial region of the masseter muscle, and in the anterior region of the temporal muscle. For fast b MyHC fibers no significant changes were registered. This can be seen as a shift directed to slow MyHC, confirming results of the training effect in sport and rehabilitation medicine.

The effect on mechanical pain threshold over human muscles by oral administration of granisetron and diclofenac-sodium

Previous studies indicate that plasma levels of serotonin (5-HT) and intramuscular prostaglandin E 2 (PGE 2) participate in determining the mechanical pain threshold and tolerance level to pressure applied on the skin over healthy muscles. Other studies reported gender differences regarding responses to noxious stimuli. The present study aimed to determine whether the mechanical pain threshold of healthy muscles is influenced by oral administration of 5-HT 3 or PGE 2-inhibitors and if there are any gender differences in this respect. Ten healthy female subjects and 10 age-matched healthy male subjects participated in the study, which was randomized and double blind with crossover design. Granisetron (5-HT 3-antagonist), diclofenac-sodium (PGE 2-antagonist) and placebo were administered for 3 days. The pressure pain threshold (PPT) was recorded bilaterally with an algometer over certain orofacial, trunk, and limb muscles before and after administration of the antagonists. The PPT over all muscles combined increased after administration of granisetron. There was no change after administration of placebo. The difference between granisetron and placebo was significant for the trapezius and tibialis anterior muscles. Diclofenac-sodium did not influence the PPT and there was no difference compared to placebo. Although the basal PPT values were lower in females, the PPT response to granisetron differed significantly between genders only in the tibialis anterior muscle. In conclusion, the results of this study showed that oral administration of the 5-HT 3-antagonist granisetron increased the PPT over healthy trunk and limb muscles but not over orofacial muscles, and that the response in the limb muscles was greater in males.

Evolution of the brainstem orofacial motor system in primates: a comparative study of trigeminal, facial, and hypoglossal nuclei

The trigeminal motor (Vmo), facial (VII), and hypoglossal (XII) nuclei of the brainstem comprise the final common output for neural control of most orofacial muscles. Hence, these cranial motor nuclei are involved in the production of adaptive behaviors such as feeding, facial expression, and vocalization. We measured the volume and Grey Level Index (GLI) of Vmo, VII, and XII in 47 species of primates and examined these nuclei for scaling patterns and phylogenetic specializations. Allometric regression, using medulla volume as an independent variable, did not reveal a significant difference between strepsirrhines and haplorhines in the scaling of Vmo volume. In addition, correlation analysis using independent contrasts did not find a relationship between Vmo size or GLI and the percent of leaves in the diet. The scaling trajectory of VII volume, in contrast, differed significantly between suborders. Great ape and human VII volumes, furthermore, were significantly larger than predicted by the haplorhine regression. Enlargement of VII in these taxa may reflect increased differentiation of the facial muscles of expression and greater utilization of the visual channel in social communication. The independent contrasts of VII volume and GLI, however, were not correlated with social group size. To examine whether the human hypoglossal motor system is specialized to control the tongue for speech, we tested human XII volume and GLI for departures from nonhuman haplorhine prediction lines. Although human XII volumes were observed above the regression line, they did not exceed prediction intervals. Of note, orang-utan XII volumes had greater residuals than humans. Human XII GLI values also did not differ from allometric prediction. In sum, these findings indicate that the cranial orofacial motor nuclei evince a mosaic of phylogenetic specializations for innervation of the facial muscles of expression in the context of a generally conservative scaling relationship with respect to medulla size.

Commentary

HIGHLIGHTED TOPICSNeural Control of MovementCommentaryGary C. SieckGary C. SieckPublished Online:01 Jun 2004https://doi.org/10.1152/japplphysiol.00311.2004MoreSectionsPDF (13 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat The dynamics of force generation has been well studied in limb muscles, but far less is known about such dynamics in orofacial muscles. In a featured article entitled “Fast force-generation dynamics of human articulatory muscles,” Dr. T. Ito and colleagues (1) explored the force-generation dynamics of the human articulatory muscles of the upper and lower lips and tongue, using arm muscles to obtain comparative measurements in limb muscle. Twitch force responses were induced by electrical stimulations in these muscles. The dynamic responses were modeled as a second order of dynamics, with model parameters identified using a nonlinear least squares method. The measured force responses fit the estimated model parameters, which suggested that lip and tongue muscles generate forces significantly faster than arm muscles. Faster dynamics of force generation enable the articulatory muscles to respond to motor commands for generating fast speech movements. This finding is important for investigating the mechanisms of speech motor control and for building a computational model of speech articulation. Another notable aspect of this study is the methodological advantage of using electrical stimulation to activate muscle fibers. The dynamics of human muscle have traditionally been studied with the use of muscle force responses generated by tasks involving voluntary contraction. However, as this study demonstrates, voluntary tasks are not appropriate for identifying the upper limit of the dynamics of force generation, possibly because fast-twitch muscle fibers are not activated during voluntary tasks. In addition to providing essential information for studies of speech motor control and speech articulation, the findings of this study highlight the advantage of using electrical stimulation for estimating the upper limit of the dynamics of force generation in human muscle. References 1 Ito T, Murano EZ, and Gomi H. Fast force-generation dynamics of human articulatory muscles. J Appl Physiol 96: 2318-2324, 2004.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 96Issue 6June 2004Pages 2317-2317 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00311.2004History Published online 1 June 2004 Published in print 1 June 2004 Metrics

A model of l-DOPA-induced dyskinesia in 6-hydroxydopamine lesioned mice: relation to motor and cellular parameters of nigrostriatal function

l-DOPA-induced dyskinesia is a major complication of l-DOPA pharmacotherapy in Parkinson's disease, and is thought to depend on abnormal cell signaling in the basal ganglia. In this study, we have addressed the possibility to model l-DOPA-induced dyskinesia in the mouse at both the behavioral and the molecular level. C57BL/6 mice sustained unilateral injections of 6-hydroxydopamine (6-OHDA) either in the medial forebrain bundle (MFB) or in the sensorimotor part of the striatum. Both types of lesion produced a similar degree of forelimb akinesia on the contralateral side of the body. The lowest dose of l-DOPA that could significantly relieve this akinetic deficit (i.e., 6 mg/kg) did not differ between MFB and intrastriatal lesions. The l-DOPA threshold dose for the induction of dyskinesia did however differ between the two lesion types. A daily dose of 6 mg/kg l-DOPA caused MFB lesioned mice to develop abnormal movements affecting orofacial, trunk, and forelimb muscles on the side contralateral to the lesion, whereas a daily dose of 18 mg/kg was required to produce comparable dyskinetic effects in the intrastriatally lesioned animals. The development of abnormal movements was accompanied by a striatal induction of ΔFosB-like proteins and prodynorphin mRNA, that is, molecular markers that are associated with l-DOPA-induced dyskinesia in both rats and nonhuman primates. We conclude that 6-OHDA lesioned mice exhibit behavioral and cellular features of akinesia and l-DOPA-induced dyskinesia that are similar to those previously characterized in rats. The mouse model of l-DOPA-induced dyskinesia will provide a useful tool to study the molecular determinants of this movement disorder in transgenic mice strains.

Cortical Orofacial Motor Representation in Old World Monkeys, Great Apes, and Humans

This study presents a comparative stereologic investigation of neurofilament protein- and calcium-binding protein-immunoreactive neurons within the region of orofacial representation of primary motor cortex (Brodmann’s area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens). Results showed that the density of interneurons involved in vertical interlaminar processing (i.e., calbindin- and calretinin-immunoreactive neurons) as well pyramidal neurons that supply heavily-myelinated projections (i.e., neurofilament protein-immunoreactive neurons) are correlated with overall neuronal density, whereas interneurons making transcolumnar connections (i.e., parvalbumin-immunoreactive neurons) do not exhibit such a relationship. These results suggest that differential scaling rules apply to different neuronal subtypes depending on their functional role in cortical circuitry. For example, cortical columns across catarrhine species appear to involve a similar conserved network of intracolumnar inhibitory interconnections, as represented by the distribution of calbindin- and calretinin-immunoreactive neurons. The subpopulation of horizontally-oriented wide-arbor interneurons, on the other hand, increases in density relative to other interneuron subpopulations in large brains. Due to these scaling trends, the region of orofacial representation of primary motor cortex in great apes and humans is characterized by a greater proportion of neurons enriched in neurofilament protein and parvalbumin compared to the Old World monkeys examined. These modifications might contribute to the voluntary dexterous control of orofacial muscles in great ape and human communication.

Cortical Orofacial Motor Representation in Old World Monkeys, Great Apes, and Humans

Social life in anthropoid primates is mediated by interindividual communication, involving movements of the orofacial muscles for the production of vocalization and gestural expression. Although phylogenetic diversity has been reported in the auditory and visual communication systems of primates, little is known about the comparative neuroanatomy that subserves orofacial movement. The current study reports results from quantitative image analysis of the region corresponding to orofacial representation of primary motor cortex (Brodmann’s area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens) using the Grey Level Index method. This cortical region has been implicated in the execution of skilled motor activities such as voluntary facial expression and human speech. Density profiles of the laminar distribution of Nissl-stained neuronal somata were acquired from high-resolution images to quantify cytoarchitectural patterns. Despite general similarity in these profiles across catarrhines, multivariate analysis showed that cytoarchitectural patterns of individuals were more similar within-species versus between-species. Compared to Old World monkeys, the orofacial representation of area 4 in great apes and humans was characterized by an increased relative thickness of layer III and overall lower cell volume densities, providing more neuropil space for interconnections. These phylogenetic differences in microstructure might provide an anatomical substrate for the evolution of greater volitional fine motor control of facial expressions in great apes and humans.

Effects of bilateral resection of facial nerves on suckling in developing rats

The purpose of the present study is to investigate functional role of the facial nerve on suckling in developing rats. The bilateral resection of facial nerves on postnatal day 1 (P1) resulted in cell loss of facial motoneurons and complete facial paralysis without any whisker movement or nictitating reflex at the end of the postnatal 3 weeks. Although the body weight of the nerve-resected rats increased gradually for the postnatal 3 weeks, they weighed less than the control rats without nerve resection. The nerve-resected rats contained less milk (0.25±0.02 g) than the control rats (0.35±0.02 g) in the stomach on P17. On P21, the body weight of the nerve-resected rats (25.33±0.32 g) was decreased by 28% compared to that of the control rats (35.08±0.57 g). Although their growth was substantially more retarded than that of the control animals, most (92%) of the nerve-resected pups could survive without facial nerve innervation. The orofacial musculature innervated by the facial nerve plays an important role in breastfeeding, but the present study shows that these muscles are not essential for the survival of neonatal rats.

Association of orofacial muscle activity and movement during changes in speech rate and intensity.

Understanding how orofacial muscle activity and movement covary across changes in speech rate and intensity has implications for the neural control of speech production and the use of clinical procedures that manipulate speech prosody. The present study involved a correlation analysis relating average lower-lip and jaw-muscle activity to lip and jaw movement distance, speed, and duration. Recordings were obtained on orofacial movement, muscle activity, and the acoustic signal in 3 normal speakers as they repeated a simple test utterance with targeted speech rates varying from 60% to 160% of their habitual rate and at targeted vocal intensities of -6 dB and +6 dB relative to their habitual intensity. Surface electromyographic (EMG) recordings were obtained with electrodes positioned to sample primarily the mentalis, depressor labii inferior, anterior belly of the digastric, and masseter muscles. Two-dimensional displacements of the lower lip and jaw in the midsagittal plane were recorded with an electromagnetic system. All participants produced linear changes in percent utterance duration relative to the auditory targets for speech rate variation. Intensity variations ranged from -10 dB to +8 dB. Average EMG levels for all 4 muscles were well correlated with specific parameters of movement. Across the intensity conditions, EMG level was positively correlated with movement speed and distance in all participants. Across the rate conditions, EMG level was negatively correlated with movement duration in all participants, while greater interparticipant variability was noted for correlations relating EMG to speed and distance. For intensity control, it is suggested that converging neural input to orofacial motoneurons varies monotonically with movement distance and speed. In contrast, rate control appears to be more strongly related to the temporal characteristics of neural input than activation level.

Effects of low-power laser exposure on masseter muscle pain and microcirculation

One possible cause of the reported positive treatment effect by low-power laser exposure in muscle pain conditions could be that it increases the local microcirculation. The aim of this study was therefore to investigate the immediate effects on masseter muscle blood flow by low-power laser exposure in patients with chronic orofacial pain of muscular origin in comparison to healthy individuals. Twelve patients with myofascial pain of orofacial muscles and 12 age and gender matched healthy individuals participated in the study. Before laser exposure the subjects were examined clinically and the patients scored their current pain intensity from the most tender masseter muscle. Intramuscular laser-Doppler flowmetry was performed unilaterally in the most tender point (patients) or in a standardized point (healthy subjects) of the masseter muscle. The muscle was first exposed with a Gallium–Aluminum–Arsenide laser (active laser) or placebo laser for 2 min in a randomized and double-blind manner. After another 8 min the muscle was treated with the other laser for 2 min and the LDF recording continued for 8 min. Finally, the patients again assessed the pain intensity. Data were analyzed blindly by one of the authors not participating in data collection. The pain intensity was not affected by laser exposure. The blood flow did not change significantly in the patients, but increased after active laser exposure and decreased after placebo exposure in the healthy individuals. The difference between active laser and placebo was significant. In conclusion, the results of this study do not support an effect of low-power laser exposure on masseter muscle microcirculation in patients with chronic orofacial pain of muscular origin.

Cerebellar speech representation: lesion topography in dysarthria as derived from cerebellar ischemia and functional magnetic resonance imaging.

Lesion topography and the pathophysiological background of dysarthria due to focal cerebellar lesions have not yet been fully clarified. To investigate the lesion topography of dysarthria due to cerebellar ischemia and evaluate brainstem functions. Case studies. Eighteen right-handed patients with sudden-onset dysarthria and cerebellar ischemia with and without brainstem involvement and 19 healthy, right-handed, monolingual, German-speaking volunteers. In patients, we used multimodal electrophysiologic techniques to investigate brainstem functions. Functional magnetic resonance imaging (MRI) was performed in the 19 healthy volunteers. Activation tasks consisted of repetitive vertical silent movements of the tongue and lips at a self-paced rhythm. Cerebellar lesions and additional signs of brainstem involvement were observed in 11 patients with posterior inferior cerebellar artery, anterior inferior cerebellar artery, and superior cerebellar artery infarctions, respectively. In all other patients with isolated cerebellar infarction (n = 7), only the superior cerebellar artery territory (6 right-sided, 1 left-sided) was affected, and the common lesion site was the rostral paravermal region of the anterior lobe. Functional MRI in healthy volunteers indicated that the cerebellar representation of the tongue and orofacial muscles corresponds to that of the area involved in patients with cerebellar dysarthria. The results of this study demonstrate that articulatory movements of the tongue and orofacial muscles are involved in the activation of the rostral paravermal area of the anterior lobe. This location corresponds to the area involved in cerebellar ischemia in patients with dysarthria. Lesions in the upper paravermal area of the right cerebellar hemisphere, the site of coordination of articulatory movements of the tongue and orofacial muscles, may lead to the development of dysarthria that is unrelated to (often concomitant) brainstem infarctions.