Neuroplasticity of face primary motor cortex control of orofacial movements

Comparison of Objective Facial Metrics on Both Sides of the Face Among Patients with Severe Bell's Palsy Treated with Mirror Effect Plus Protocol Rehabilitation Versus Controls

Objective: The extent to which the healthy hemiface dynamically contributes to facial synchronization during facial rehabilitation has been largely unstudied. This study compares the synchronization of both hemifaces in severe Bell's palsy patients who either received facial rehabilitation called "Mirror Effect Plus Protocol" (MEPP) or basic counseling. Methods: Baseline and 1-year postonset data from 39 patients (19 = MEPP and 20 = basic counseling) were retrospectively analyzed using Emotrics+, a software that generates facial metrics with artificial intelligence (AI) algorithms. Paired t-tests were used for intrasubject comparisons of hemifaces, and mixed model analysis were used to compare between groups. Results: For voluntary movements, a significant difference in favor of the MEPP group was only found for smiling (p = 0.025*). However, at 1-year postonset, the control group showed significant variability between hemifaces for most synkinesis measurements [nasolabial fold (p = 0.029*); eye area (p = 0.043*); palpebral fissure (p = 0.011*)]. Conclusion: In this study, a better synchronization of both hemifaces was found in the MEPP group. Interestingly, motor adaptation in movement amplitude of the healthy hemiface seemed to contribute to this synchronization in MEPP patients. Further studies are needed to standardize the procedure of AI measurements and to adapt it for clinical use.

Lower masticatory function relates to cognitive health and intrinsic brain network in older adults

OBJECTIVES

Mastication is associated with brain activation at the primary somatosensory cortex (S1) and the primary motor cortex (M1). Masticatory functions differ between patients with cognitive impairment (CI) and cognitively healthy older adults (non-CI). The association between cognitive health, brain network of functional connectivity, and mastication has remained unknown. The study investigated the association between masticatory performance (MP) and the topological feature of the functional network at the M1 and S1 in the CI and non-CI groups.

SUBJECTS AND METHODS

Forty-nine non-CI and 15 CI subjects received resting-state (rs) fMRI and assessment of MP. The topological feature of the M1 and S1 was quantified by eigenvector centrality (EC), an index that reflects a brain region as a functional "hub" of brain network.

RESULTS

In the non-CI group, MP was significantly correlated with EC of the left M1 and the right M1. The correlation was not statistically significant in the CI group. Cognitive status (CI or non-CI) and EC of the left M1 and the right M1, respectively, were statistically significant predictors to individual MP.

CONCLUSION

Cognitive status and the topological feature of the M1 in the intrinsic functional network may contribute to the individual difference in masticatory function.

Links Between Swallowing and Consciousness: A Narrative Review

This literature review explores a wide range of themes addressing the links between swallowing and consciousness. Signs of consciousness are historically based on the principle of differentiating reflexive from volitional behaviors. We show that the sequencing of the components of swallowing falls on a continuum of voluntary to reflex behaviors and we describe several types of volitional and non-volitional swallowing tasks. The frequency, speed of initiation of the swallowing reflex, efficacy of the pharyngeal phase of swallowing and coordination between respiration and swallowing are influenced by the level of consciousness during non-pathological modifications of consciousness such as sleep and general anesthesia. In patients with severe brain injury, the level of consciousness is associated with several components related to swallowing, such as the possibility of extubation, risk of pneumonia, type of feeding or components directly related to swallowing such as oral or pharyngeal abnormalities. Based on our theoretical and empirical analysis, the efficacy of the oral phase and the ability to receive exclusive oral feeding seem to be the most robust signs of consciousness related to swallowing in patients with disorders of consciousness. Components of the pharyngeal phase (in terms of abilities of saliva management) and evoked cough may be influenced by consciousness, but further studies are necessary to determine if they constitute signs of consciousness as such or only cortically mediated behaviors. This review also highlights the critical lack of tools and techniques to assess and treat dysphagia in patients with disorders of consciousness.

Impact of oral motor task training on corticomotor pathways and diadochokinetic rates in young healthy participants

Background

Studies addressing the training‐induced neuroplasticity and interrelationships of the lip, masseter, and tongue motor representations in the human motor cortex using single syllable repetition are lacking.

Objective

This study investigated the impact of a repeated training in a novel PaTaKa diadochokinetic (DDK) orofacial motor task (OMT) on corticomotor control of the lips, masseter, and tongue muscles in young healthy participants.

Methods

A total of 22 young healthy volunteers performed 3 consecutive days of training in an OMT. Transcranial magnetic stimulation was applied to elicit motor evoked potentials (MEPs) from the lip, masseter, tongue, and first dorsal interosseous (FDI, internal control) muscles. MEPs were assessed by stimulus–response curves and corticomotor mapping at baseline and after OMT. The DDK rate from PaTaKa single syllable repetition and numeric rating scale (NRS) scores were also obtained at baseline and immediately after each OMT. Repeated‐measures analysis of variance was used to detect differences at a significance level of 5%.

Results

There was a significant effect of OMT and stimulus intensity on the lips, masseter, and tongue MEPs compared to baseline (p < .001), but not FDI MEPs (p > .05). OMT increased corticomotor topographic maps area (p < .001), and DDK rates (p < .01).

Conclusion

Our findings suggest that 3 consecutive days of a repeated PaTaKa training in an OMT can induce neuroplastic changes in the corticomotor pathways of orofacial muscles, and it may be related to mechanisms underlying the improvement of orofacial fine motor skills due to short‐term training. The clinical utility should now be investigated.

Beyond language: The unspoken sensory-motor representation of the tongue in non-primates, non-human and human primates

The English idiom "on the tip of my tongue" commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide range of studies conducted on non-primates, non-human and human primates with the aim of providing a comprehensive description of the cortical representation of the tongue's somatosensory inputs and motor outputs across different phylogenetic domains. First, we summarize how the properties of passive non-noxious mechanical stimuli are encoded in the putative somatosensory tongue area, which has a conserved location in the ventral portion of the somatosensory cortex across mammals. Second, we review how complex self-generated actions involving the tongue are represented in more anterior regions of the putative somato-motor tongue area. Finally, we describe multisensory response properties of the primate and non-primate tongue area by also defining how the cytoarchitecture of this area is affected by experience and deafferentation.

The effects of continuous oromotor activity on speech motor learning: speech biomechanics and neurophysiologic correlates

Sustained limb motor activity has been used as a therapeutic tool for improving rehabilitation outcomes and is thought to be mediated by neuroplastic changes associated with activity-induced cortical excitability. Although prior research has reported enhancing effects of continuous chewing and swallowing activity on learning, the potential beneficial effects of sustained oromotor activity on speech improvements is not well-documented. This exploratory study was designed to examine the effects of continuous oromotor activity on subsequent speech learning. Twenty neurologically healthy young adults engaged in periods of continuous chewing and speech after which they completed a novel speech motor learning task. The motor learning task was designed to elicit improvements in accuracy and efficiency of speech performance across repetitions of eight-syllable nonwords. In addition, transcranial magnetic stimulation was used to measure the cortical silent period (cSP) of the lip motor cortex before and after the periods of continuous oromotor behaviors. All repetitions of the nonword task were recorded acoustically and kinematically using a three-dimensional motion capture system. Productions were analyzed for accuracy and duration, as well as lip movement distance and speed. A control condition estimated baseline improvement rates in speech performance. Results revealed improved speech performance following 10 min of chewing. In contrast, speech performance following 10 min of continuous speech was degraded. There was no change in the cSP as a result of either oromotor activity. The clinical implications of these findings are discussed in the context of speech rehabilitation and neuromodulation.

Chewing function and related parameters as a function of the degree of dementia: Is there a link between the brain and the mouth?

Background

To date, no study has investigated the association between chewing function and related parameters as a function of the degree of dementia using a finer subdivision of the values of the Mini‐Mental State Examination (MMSE).

Objective

This study aimed to investigate the differences in chewing function and related parameters as a function of the degree of dementia.

Methods

An analysis of cross‐sectional data obtained from the OrBiD (Oral Health, Bite Force, and Dementia) pilot study was performed. The participants were stratified into five groups based on the outcomes of the MMSE (no dementia, MMSE 28–30; mild cognitive impairment, MMSE 25–27; mild dementia, MMSE 18–24; moderate dementia, MMSE 10–17; severe dementia, MMSE <10). The chewing efficiency, maximum occlusal force and related parameters (number of supporting zones, number of teeth, Eichner index, tooth/denture status, denture quality, and dental treatment needs) were recorded.

Results

The MMSE groups showed significantly different chewing efficiencies (p = .003, Jonckheere‐Terpstra test) and maximum occlusal forces (p = .003, Jonckheere‐Terpstra test), but the number of supporting zones (p = .055, chi‐square test) and the number of natural teeth (p = .126, chi‐square test) were not different. The Eichner index, tooth/denture status, denture quality and dental treatment need showed no significant associations with the degree of dementia.

Conclusion

An improvement in the usability of the measurement methods for assessing chewing function in people with dementia is needed. Research involving people with dementia is necessary because the nutritional situation often deteriorates rapidly within a multifactorial system, which includes chewing ability and oral health.

Bite Force in Elderly with Full Natural Dentition and Different Rehabilitation Prosthesis

(1) Background: This study aimed to investigate maximum bite force (MBF) in elderly patients with natural full dentition (FD), patients rehabilitated with Traditional Complete Dentures (CD), with overdentures (IRO) and edentulous patients (ED). We also tested whether MBF changes are associated with gender, age of the patients and body mass index (BMI) as result of altered food; (2) Methods: Three hundred and sixty-eight geriatric patients were included. We studied two types of prostheses: (a) IRO with telescopic attachments. (b) CD (heat polymerized polymethyl methacrylate resin). The MBF was measured using a digital dynamometer with a bite fork; (3) Results: We found that MBF is higher in males than females, regardless of teeth presence or absence (p < 0.01). In patients with CD or IRO, there are no differences between males and females; prostheses improve MBF compared to edentulous patients (p < 0.0001) and this effect is greater with IRO prostheses (p < 0.0001); the chewing force of FD subjects remains greater (p < 0.0001); there are no differences among chewing strength based on different BMI categories, although FD subjects have a reduced incidence of obesity; there is a significant negative correlation between MBF and age (p = 0.038; R = 0.145), and no correlation between MBF and BMI; (4) Conclusions: This study showed that MBF improves more in patients using IRO prostheses, although not reaching the MBF of FD subjects. MBF does not correlate with BMI, although we found increased percentages of obesity in edentulous subjects or those with prostheses. Thus, old people wearing prostheses require special attention by a nutritionist to avoid risk of malnutrition.

The Mirror Effect Plus Protocol for acute Bell's palsy: a randomised and longitudinal study on facial rehabilitation

BACKGROUND

Small but interesting evidences suggest that facial rehabilitation for acute Bell Palsy (BP) could improve facial outcomes in patients who benefited from optimal medication, but whose symptoms are still severe two weeks after BP's onset.

AIMS

This study aimed to provide preliminary evidence of the long-term effects of a new facial retraining based on motor imagery and mirror therapy, the Mirror Effect Plus Protocol (MEPP).

MATERIAL AND METHODS

Twenty BP patients received the standard medication for acute BP and were then randomly allocated to the treatment (MEPP) or control group, if their palsy was still at least moderate-to-severe at 14 days post onset. Three blind independent assessors graded the patients' evolution until 6 months after onset.

RESULTS

Significant differences between the groups were not found for any measured variable; however, a trend toward better recovery was found in the treatment group for every measured variable. This trend grew bigger for patients with severe or total BP.

CONCLUSIONS

This study suggests a promising effect of the MEPP on acute severe to total BP but requires further investigation with a larger number of participants.

SIGNIFICANCE

Facial rehabilitation should be considered as an adjunct to medication for acute and most severe degrees of BP.

Swallowing in individuals with disorders of consciousness: A cohort study

BACKGROUND

After a period of coma, a proportion of individuals with severe brain injury remain in an altered state of consciousness before regaining partial or complete recovery. Individuals with disorders of consciousness (DOC) classically receive hydration and nutrition through an enteral-feeding tube. However, the real impact of the level of consciousness on an individual's swallowing ability remains poorly investigated.

OBJECTIVE

We aimed to document the incidence and characteristics of dysphagia in DOC individuals and to evaluate the link between different components of swallowing and the level of consciousness.

METHODS

We analyzed clinical data on the respiratory status, oral feeding and otolaryngologic examination of swallowing in DOC individuals. We analyzed the association of components of swallowing and participant groups (i.e., unresponsive wakefulness syndrome [UWS] and minimally conscious state [MCS]).

RESULTS

We included 92 individuals with DOC (26 UWS and 66 MCS). Overall, 99% of the participants showed deficits in the oral and/or pharyngeal phase of swallowing. As compared with the MCS group, the UWS group more frequently had a tracheostomy (69% vs 24%), with diminished cough reflex (27% vs 54%) and no effective oral phase (0% vs 21%).

CONCLUSION

Almost all DOC participants had severe dysphagia. Some components of swallowing (i.e., tracheostomy, cough reflex and efficacy of the oral phase of swallowing) were related to consciousness. In particular, no UWS participant had an efficient oral phase, which suggests that its presence may be a sign of consciousness. In addition, no UWS participant could be fed entirely orally, whereas no MCS participant orally received ordinary food. Our study also confirms that objective swallowing assessment can be successfully completed in DOC individuals and that specific care is needed to treat severe dysphagia in DOC.

A limited range of vagus nerve stimulation intensities produce motor cortex reorganization when delivered during training

Pairing vagus nerve stimulation (VNS) with rehabilitation has emerged as a potential strategy to improve recovery after neurological injury, an effect ascribed to VNS-dependent enhancement of synaptic plasticity. Previous studies demonstrate that pairing VNS with forelimb training increases forelimb movement representations in motor cortex. However, it is not known whether VNS-dependent enhancement of plasticity is restricted to forelimb training or whether VNS paired with other movements could induce plasticity of other motor representations. We tested the hypothesis that VNS paired with orofacial movements associated with chewing during an unskilled task would drive a specific increase in jaw representation in motor cortex compared to equivalent behavioral experience without VNS. Rats performed a behavioral task in which VNS at a specified intensity between 0 and 1.2 mA was paired with chewing 200 times per day for five days. Intracortical microstimulation (ICMS) was then used to document movement representations in motor cortex. VNS paired with chewing at 0.8 mA significantly increased motor cortex jaw representation compared to equivalent behavioral training without stimulation (Bonferroni-corrected unpaired t-test, p < 0.01). Higher and lower intensities failed to alter cortical plasticity. No changes in other movement representations or total motor cortex area were observed between groups. These results demonstrate that 0.8 mA VNS paired with training drives robust plasticity specific to the paired movement, is not restricted to forelimb representations, and occurs with training on an unskilled task. This suggests that moderate intensity VNS may be a useful adjuvant to enhance plasticity and support benefits of rehabilitative therapies targeting functions beyond upper limb movement.

An fMRI Study of the Brain Network Involved in Teeth Tapping in Elderly Adults

Cortical activity during jaw movement has been analyzed using various non-invasive brain imaging methods, but the contribution of orofacial sensory input to voluntary jaw movements remains unclear. In this study, we used functional magnetic resonance imaging (fMRI) to observe brain activities during a simple teeth tapping task in adult dentulous (AD), older dentulous (OD), and older edentulous subjects who wore dentures (OEd) or did not wear dentures (OE) to analyze their functional network connections. (1) To assess the effect of age on natural activation patterns during teeth tapping, a comparison of groups with natural dentition—AD and OD—was undertaken. A general linear model analysis indicated that the major activated site in the AD group was the primary sensory cortex (SI) and motor cortex (MI) (p < 0.05, family wise error corrected). In the OD group, teeth tapping induced brain activity at various foci (p < 0.05, family wise error corrected), including the SI, MI, insula cortex, supplementary motor cortex (SMC)/premotor cortex (PMA), cerebellum, thalamus, and basal ganglia in each group. (2) Group comparisons between the OD and OEd subjects showed decreased activity in the SI, MI, Brodmann’s area 6 (BA6), thalamus (ventral posteromedial nucleus, VPM), basal ganglia, and insular cortex (p ¡ 0.005, uncorrected). This suggested that the decreased S1/M1 activity in the OEd group was related to missing teeth, which led to reduced periodontal afferents. (3) A conjunction analysis in the OD and OEd/OE groups revealed that commonly activated areas were the MI, SI, cerebellum, BA6, thalamus (VPM), and basal ganglia (putamen; p < 0.05, FWE corrected). These areas have been associated with voluntary movements. (4) Psychophysiological interaction analysis (OEd vs OE) showed that subcortical and cortical structures, such as the MI, SI, DLPFC, SMC/PMA, insula cortex, basal ganglia, and cerebellum, likely function as hubs and form an integrated network that participates in the control of teeth tapping. These results suggest that oral sensory inputs are involved in the control of teeth tapping through feedforward control of intended movements, as well as feedback control of ongoing movements.

Functional Connectivity Evoked by Orofacial Tactile Perception of Velocity

The cortical representations of orofacial pneumotactile stimulation involve complex neuronal networks, which are still unknown. This study aims to identify the characteristics of functional connectivity (FC) evoked by three different saltatory velocities over the perioral and buccal surface of the lower face using functional magnetic resonance imaging in twenty neurotypical adults. Our results showed a velocity of 25 cm/s evoked stronger connection strength between the right dorsolateral prefrontal cortex and the right thalamus than a velocity of 5 cm/s. The decreased FC between the right secondary somatosensory cortex and right posterior parietal cortex for 5-cm/s velocity versus all three velocities delivered simultaneously (“All ON”) and the increased FC between the right thalamus and bilateral secondary somatosensory cortex for 65 cm/s vs “All ON” indicated that the right secondary somatosensory cortex might play a role in the orofacial tactile perception of velocity. Our results have also shown different patterns of FC for each seed (bilateral primary and secondary somatosensory cortex) at various velocity contrasts (5 vs 25 cm/s, 5 vs 65 cm/s, and 25 vs 65 cm/s). The similarities and differences of FC among three velocities shed light on the neuronal networks encoding the orofacial tactile perception of velocity.

Effect of Sudden Deprivation of Sensory Inputs From Periodontium on Mastication

Objective

To investigate the effect of sudden deprivation of sensory inputs from the periodontium on jaw kinematics and time-varying activation profile of the masseter muscle.

Methods

Fourteen (age range: 22–26 years; four men) healthy and natural dentate volunteers participated in a single experimental session. During the experiment, the participants were asked to eat six hard visco-elastic test food models, three each before and after an anesthetic intervention. The movements of the jaw in three dimensions and electromyographic (EMG) activity of the masseter muscle on the chewing side were recorded.

Results

The results of the study showed no significant differences in the number of chewing cycles (P = 0.233) and the duration of chewing sequence (P = 0.198) due to sudden deprivation of sensory inputs from the periodontium. However, there was a significant increase in the jaw opening velocity (P = 0.030) and a significant increase in the duration of occlusal phase (P = 0.004) during the anesthetized condition. The EMG activity of the jaw closing phase was significantly higher during the control condition [116.5 arbitrary units (AU)] than anesthetized condition (93.9 AU). The temporal profile of the masseter muscle showed a biphasic increase in the excitatory muscle drive in the control condition but this increase was virtually absent during the anesthetized condition.

Conclusion

Sudden deprivation of sensory inputs from the periodontium affects the jaw kinematics and jaw muscle activity, with a clear difference in the time-varying activation profile of the masseter muscle. The activation profile of the masseter muscle shows that periodontal mechanoreceptors contribute to approximately 20% of the EMG activity during the jaw closing phase.

Effects of Motor Training on Accuracy and Precision of Jaw and Finger Movements

Objective

To compare the effects of training of jaw and finger movements with and without visual feedback on precision and accuracy.

Method

Twenty healthy participants (10 men and 10 women; mean age 24.6 ± 0.8 years) performed two tasks: a jaw open-close movement and a finger lifting task with and without visual feedback before and after 3-day training. Individually determined target positions for the jaw corresponded to 50% of the maximal jaw opening position, and a fixed target position of 20 mm was set for the finger. Movements were repeated 10 times each. The variability in the amplitude of the movements was expressed as percentage in relation to the target position (D_accu—accuracy) and as coefficient of variation (CV_prec—precision).

Result

D_accu and CV_prec were significantly influenced by visual feedback (P = 0.001 and P < 0.001, respectively) and reduced after training jaw and finger movements (P < 0.001). D_accu (P = 0.004) and CV_prec (P = 0.019) were significantly different between jaw and finger movements. The relative changes in D_accu (P = 0.017) and CV_prec (P = 0.027) were different from pretraining to posttraining between jaw and finger movements.

Conclusion

The accuracy and precision of standardized jaw and finger movements are dependent on visual feedback and appears to improve more by training in the trigeminal system possibly reflecting significant neuroplasticity in motor control mechanisms.

Dental occlusion as one cause of tinnitus

There is large support in literature linking tinnitus to dental occlusion and temporomandibular joint disorders (TMD). However, there is no model to explain such a link. This hypothesis explains how the fusimotor system of the muscles innervated by the trigeminal motor nucleus is affected by inadequacies in the occlusion of the teeth that cause changes in posture and movement of the mandible. Reptile to mammal evolution shows that stomatognathic structures underwent changes related to mastication. Among several changes, there was the appearance of a new articulation between the mandible and skull: the temporomandibular joint. The bones of the old reptile joint, quadrate-articular, have detached from the mandible and are part of the middle ear bone chain. The former becomes the incus and the latter the malleus. This bone change also carried the tensor tympani and its trigeminal motor innervation. Inadequate occlusal contacts give rise to an adapted function of the mandible and the most common compensatory muscular response is hypertonia involving all mandibular muscles, including the tensor tympani. A fundamental clinical feature that demonstrates the involvement of the trigeminal fusimotor system is the characteristic pain by palpation, but no pain on the mandibular movement. Muscle pain is always felt in the dermatome innervated by the mandibular branch of the trigeminal nerve, which carries the motor fibers, reported as tightening, similar to cramp, and has regular behavior in intensity, duration and frequency. In addition, the patient has increased musculature volume, detected by palpation of certain anatomical landmarks, but with loss of functional efficiency. The neuromotor control of the mandibular movements is poor and when asked to make lateral jaw movement touching the teeth, it is common to observe that the patient moves the lips, eyes, and even turns the head in the same direction as the movement. There is also difficulty eating hard foods and talking fast. Tongue biting while chewing is frequent, meaning that these non-physiological events surpass protective reflex circuits. The report of ear pain, tinnitus, blocked ear sensation and sudden hearing loss is common in such patients, compatible with the tonic contraction of the tensor tympani. The fusimotor system hypothesis is able to explain all events related to the symptoms and helps to establish a correct diagnosis for certain types of hearing disorders.

Structure-Function Relationships of the Temporomandibular Joint in Response to Altered Loading

AIMS

To elucidate the effects of decreased occlusal loading (DOL), with or without reloading (RL), on the structure and bite force function of the mandibular condylar fibrocartilage in skeletally mature male mice.

METHODS

At 13 weeks old, 30 wild type (WT) male mice were subjected to: (1) 6 weeks normal loading (NL); (2) 6 weeks DOL; or (3) 4 weeks DOL + 2 weeks RL. Histomorphometry, cell metabolic activity, gene expression of chondrogenic markers, and bite force tests were performed.

RESULTS

DOL resulted in a significant increase in apoptosis (P < .0001) and significant decreases in fibrocartilage thickness (P < .05) and hypertrophic chondrocyte markers indian hedgehog and collagen type X (P < .05). A corresponding decrease in bite force was also observed (P < .05). RL treatment resulted in a return to values comparable to NL of chondrogenic maturation markers (P > .10), apoptosis (P > .999), and bite force (P > .90), but not in mandibular condylar fibrocartilage thickness (P > .05).

CONCLUSIONS

DOL in skeletally mature mice induces mandibular condylar fibrocartilage atrophy at the hypertrophic cell layer with a corresponding decrease in bite force.

The role of EEG and EMG combined virtual reality gaming system in facial palsy rehabilitation - A case report

BACKGROUND

The recovery rates for facial palsy are usually excellent; however, regularly patients present with problems with their fine facial movements that affect their emotional expressions.

OBJECTIVE

To discover the viability and ease of using an Electroencephalogram (EEG) and Electromyography (EMG) combined Virtual Reality (VR) gaming system - the 'Oculus Rift' device in the evaluation and rehabilitation of facial palsy.

DESIGN

Single case study.

PATIENT INFORMATION

A young 23-year-old female with facial palsy.

CLINICAL FINDINGS

Most of the patient's facial features were re-established within the recovery time frame, except for her right forehead and eyebrow movements.

INTERVENTION

A 10 day exercise program (Day 2-11) with an immersive virtual reality device, which randomly shoots virtually animated white balls in an unpredictable and testing pattern.

OUTCOME MEASURES

EEG and EMG patterns corresponding to the facial upper quadrant were taken at baseline, post-intervention, and at follow up.

RESULTS

EMG and EEG investigation revealed a progressive improvement in the muscle activation in response to the impulsive and unpredictable activities in the virtual environment provided through the immersive VR device.

CONCLUSION

The case report found a positive relationship between VR, facial upper quadrant EMG activation and EEG pattern changes following the intervention.

Face sensorimotor cortex undergoes neuroplastic changes in a rat model of trigeminal neuropathic pain

Trigeminal nerve injury can result in neuropathic pain behavior and alterations in motor function, but it is unclear if such injury produces neuroplastic alterations in face sensorimotor cortex that could contribute to the alterations in motor function. Therefore, this study aimed to determine if trigeminal nerve injury in a rat neuropathic pain model induces neuroplastic changes in jaw and tongue motor representations in face sensorimotor cortex in association with facial nociceptive behavior. Right infraorbital nerve transection was performed in adult male Sprague-Dawley rats; sham-operated rats served as controls. Nociceptive behavior was assessed by testing facial mechanical sensitivity pre-operatively and post-operatively (1-28 days). Intracortical microstimulation was also applied post-operatively in a series of microelectrode penetrations to map jaw and tongue motor representations in the face sensorimotor cortex by analyzing anterior digastric and genioglossus electromyographic activities evoked by microstimulation at histologically verified sites in face primary somatosensory cortex (face-SI) as well as face primary motor cortex (face-MI). Compared to sham, infraorbital nerve injury induced a significant (2-way repeated-measures analysis of variance, P < 0.001) bilateral decrease in facial mechanical threshold that lasted up to 28 days post-operatively. Nerve injury also induced a significant bilateral decrease compared to sham (P < 0.05) in the number of anterior digastric and/or genioglossus sites in face-MI and in face-SI. These findings indicate that trigeminal nerve injury induces neuroplastic alterations in jaw and tongue motor representations in face sensorimotor cortex that are associated with facial nociceptive behavior and that may contribute to sensorimotor changes following trigeminal nerve injury.

Decreased hippocampal brain-derived neurotrophic factor and impaired cognitive function by hypoglossal nerve transection in rats

The hypoglossal nerve controls tongue movements, and damages of it result in difficulty in mastication and food intake. Mastication has been reported to maintain hippocampus‐dependent cognitive function. This study was conducted to examine the effect of tongue motor loss on the hippocampus‐dependent cognitive function and its underlying mechanism. Male Sprague Dawley rats were subjected to the initial training of Morris water maze task before or after the bilateral transection of hypoglossal nerves (Hx). When the initial training was given before the surgery, the target quadrant dwelling time during the probe test performed at a week after the surgery was significantly reduced in Hx rats relative to sham‐operated controls. When the initial training was given after the surgery, Hx affected the initial and reversal trainings and probe tests. Brain‐derived neurotrophic factor (BDNF) expression, cell numbers and long‐term potentiation (LTP) were examined in the hippocampus on the 10^th day, and BrdU and doublecortin staining on the 14^th day, after the surgery. Hx decreased the hippocampal BDNF and cells in the CA1/CA3 regions and impaired LTP. BrdU and doublecortin staining was decreased in the dentate gyrus of Hx rats. Results suggest that tongue motor loss impairs hippocampus‐dependent cognitive function, and decreased BDNF expression in the hippocampus may be implicated in its underlying molecular mechanism in relation with decreased neurogenesis/proliferation and impaired LTP.

Perturbed oral motor control due to anesthesia during intraoral manipulation of food

Sensory information from periodontal mechanoreceptors (PMRs) surrounding the roots of natural teeth is important for optimizing the positioning of food and adjustment of force vectors during precision biting. The present experiment was designed to test the hypothesis; that reduction of afferent inputs from the PMRs, by anesthesia, perturbs the oral fine motor control and related jaw movements during intraoral manipulation of morsels of food. Thirty healthy volunteers with a natural dentition were equally divided into experimental and control groups. The participants in both groups were asked to manipulate and split a spherical candy into two equal halves with the front teeth. An intervention was made by anesthetizing the upper and lower incisors of the experimental group while the control group performed the task without intervention. Performance of the split was evaluated and the jaw movement recorded. The experimental group demonstrated a significant decrease in measures of performance following local anesthesia. However, there was no significant changes in the duration or position of the jaw during movements in the experimental and control group. In conclusion, transient deprivation of sensory information from PMRs perturbs oral fine motor control during intraoral manipulation of food, however, no significant alterations in duration or positions of the jaw during movements can be observed.

Unilateral nasal obstruction affects motor representation development within the face primary motor cortex in growing rats

Postnatal growth is influenced by genetic and environmental factors. Nasal obstruction during growth alters the electromyographic activity of orofacial muscles. The facial primary motor area represents muscles of the tongue and jaw, which are essential in regulating orofacial motor functions, including chewing and jaw opening. This study aimed to evaluate the effect of chronic unilateral nasal obstruction during growth on the motor representations within the face primary motor cortex (M1). Seventy-two 6-day-old male Wistar rats were randomly divided into control (n = 36) and experimental (n = 36) groups. Rats in the experimental group underwent unilateral nasal obstruction after cauterization of the external nostril at 8 days of age. Intracortical microstimulation (ICMS) mapping was performed when the rats were 5, 7, 9, and 11 wk old in control and experimental groups (n = 9 per group per time point). Repeated-measures multivariate ANOVA was used for intergroup and intragroup statistical comparisons. In the control and experimental groups, the total number of positive ICMS sites for the genioglossus and anterior digastric muscles was significantly higher at 5, 7, and 9 wk, but there was no significant difference between 9 and 11 wk of age. Moreover, the total number of positive ICMS sites was significantly smaller in the experimental group than in the control at each age. It is possible that nasal obstruction induced the initial changes in orofacial motor behavior in response to the altered respiratory pattern, which eventually contributed to face-M1 neuroplasticity.NEW & NOTEWORTHY Unilateral nasal obstruction in rats during growth periods induced changes in arterial oxygen saturation (SpO₂) and altered development of the motor representation within the face primary cortex. Unilateral nasal obstruction occurring during growth periods may greatly affect not only respiratory function but also craniofacial function in rats. Nasal obstruction should be treated as soon as possible to avoid adverse effects on normal growth, development, and physiological functions.

Does altered mandibular position and dental occlusion influence upper cervical movement: A cross-sectional study in asymptomatic people

OBJECTIVE

Gross mandibular position and masticatory muscle activity have been shown to influence cervical muscles electromyographic activity. The purpose of this study was to investigate the influence of three different mandible positions including conscious occlusion, tongue tip against the anterior hard palate (Palate tongue position) and natural resting position (Rest), on sagittal plane cervical spine range of motion (ROM) as well as the flexion-rotation test (FRT) in asymptomatic subjects.

MATERIALS AND METHODS

An experienced single blinded examiner evaluated ROM using an Iphone in 22 subjects (7 females; mean age of 29.91years, SD 5.44).

RESULTS

Intra-rater reliability for range recorded was good for the FRT with ICC (intraclass correlation) 0.95 (95% CI: 0.88-0.98) and good for sagittal plane cervical ROM with ICC 0.90 (95% CI: 0.77-0.96). A repeated measures ANOVA determined that mean ROM recorded during the FRT differed significantly between assessment points (F(1.99, 41.83) = 19.88, P < 0.001). Bonferroni Post hoc tests revealed that both conscious Occlusion and Palate tongue position elicited a significant large reduction in ROM recorded during the FRT from baseline (p < 0.01). Despite this, one activation strategy did not influence ROM more than the other. An additional repeated measures ANOVA determined that mean sagittal cervical ROM did not significantly vary between assessment points (F(2, 42) = 8.18, P = 0.08).

CONCLUSION

This current study provided further evidence for the influence of the temporomandibular region on upper cervical ROM. Results suggest that clinicians should focus on the natural mandible rest position when evaluating upper cervical mobility.

Investigating complex basal ganglia circuitry in the regulation of motor behaviour, with particular focus on orofacial movement

Current concepts of basal ganglia function have evolved from the essentially motoric, to include a range of extramotoric functions that involve not only dopaminergic but also cholinergic, γ-aminobutyric acid (GABA)ergic and glutamatergic mechanisms. We consider these mechanisms and their efferent systems, including spiralling, feed-forward striato-nigro-striatal circuitry, involving the dorsal and ventral striatum and the nucleus accumbens (NAc) core and shell. These processes are illustrated using three behavioural models: turning-pivoting, orofacial movements in rats and orofacial movements in genetically modified mice. Turning-pivoting indicates that dopamine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-nigro-striato-nigro-pedunculopontine pathway, whereas acetylcholine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-ventral pallidum-mediodorsal thalamus pathway. Cooperative/synergistic interactions between striatal D1-like and D2-like dopamine receptors regulate individual topographies of orofacial movements that are funnelled through striatal projection pathways and involve interactions with GABAergic and glutamatergic receptor subtypes. This application of concerted behavioural, neurochemical and neurophysiological techniques implicates a network that is yet broader and interacts with other neurotransmitters and neuropeptides within subcortical, cortical and brainstem regions to 'sculpt' aspects of behaviour into its topographical collective.

Dental Occlusal Changes Induce Motor Cortex Neuroplasticity

Modification to the dental occlusion may alter oral sensorimotor functions. Restorative treatments aim to restore sensorimotor functions; however, it is unclear why some patients fail to adapt to the restoration and remain with sensorimotor complaints. The face primary motor cortex (face-M1) is involved in the generation and control of orofacial movements. Altered sensory inputs or motor function can induce face-M1 neuroplasticity. We took advantage of the continuous eruption of the incisors in Sprague-Dawley rats and used intracortical microstimulation (ICMS) to map the jaw and tongue motor representations in face-M1. Specifically, we tested the hypothesis that multiple trimming of the right mandibular incisor, to keep it out of occlusal contacts for 7 d, and subsequent incisor eruption and restoration of occlusal contacts, can alter the ICMS-defined features of jaw and tongue motor representations (i.e., neuroplasticity). On days 1, 3, 5, and 7, the trim and trim-recovered groups had 1 to 2 mm of incisal trimming of the incisor; a sham trim group had buccal surface trimming with no occlusal changes; and a naive group had no treatment. Systematic mapping was performed on day 8 in the naive, trim, and sham trim groups and on day 14 in the trim-recovered group. In the trim group, the tongue onset latency was shorter in the left face-M1 than in the right face-M1 ( P < .001). In the trim-recovered group, the number of tongue sites and jaw/tongue overlapping sites was greater in the left face-M1 than in the right face-M1 ( P = 0.0032, 0.0016, respectively), and the center of gravity was deeper in the left than in the right face-M1 ( P = 0.026). Therefore, incisor trimming and subsequent restoration of occlusal contacts induced face-M1 neuroplasticity, reflected in significant disparities between the left and right face-M1 in some ICMS-defined features of the tongue motor representations. Such neuroplasticity may reflect or contribute to subjects’ ability to adapt their oral sensorimotor functions to an altered dental occlusion.

Increasing functional connectivity of the anterior cingulate cortex during the course of recovery from Bell's palsy

Bell's palsy (BP), a unilateral and idiopathic palsy of the facial nerve, is a common disorder generally followed by a good natural recovery. The aim of this study was to investigate the relationship between the functional connectivity of the anterior cingulate cortex (ACC) and the recovery process of BP. Thirty-seven healthy volunteers and 67 patients were studied by functional MRI (fMRI). The seed regions of bilateral ACC were first extracted from the task-state fMRI data of healthy participants performing the task of mouth opening and closing. The connectivity of bilateral ACC was calculated from resting-state fMRI data of patients in whom only resting-state fMRI data were collected. The correlation between the strength of ACC's connectivity with the duration (time course of disease) was computed by analysis of covariance. It was found that the functional connectivity of the ACC ipsilateral to the lesioned side was enforced as the duration increased. The enforced brain areas included the sensorimotor areas and the ACC contralateral to the palsy. It was suggested that enforced functional connectivity of ACC might be related to cortical reorganization, which is important in the process of BP recovery.

Effects of short-term training on behavioral learning and skill acquisition during intraoral fine motor task

Sensory information from the orofacial mechanoreceptors are used by the nervous system to optimize the positioning of food, determine the force levels, and force vectors involved in biting of food morsels. Moreover, practice resulting from repetition could be a key to learning and acquiring a motor skill. Hence, the aim of the experiment was to test the hypothesis that repeated splitting of a food morsel during a short-term training with an oral fine motor task would result in increased performance and optimization of jaw movements, in terms of reduction in duration of various phases of the jaw movements. Thirty healthy volunteers were asked to intraorally manipulate and split a chocolate candy, into two equal halves. The participants performed three series (with 10 trials) of the task before and after a short-term (approximately 30 min) training. The accuracy of the split and vertical jaw movement during the task were recorded. The precision of task performance improved significantly after training (22% mean deviation from ideal split after vs. 31% before; P<0.001). There was a significant decrease in the total duration of jaw movements during the task after the training (1.21 s total duration after vs. 1.56 s before; P<0.001). Further, when the jaw movements were divided into different phases, the jaw opening phase and contact phase were significantly shorter after training than before training (P=0.001, P=0.002). The results indicate that short-term training of an oral fine motor task induces behavior learning, skill acquisition and optimization of jaw movements in terms of better performance and reduction in the duration of jaw movements, during the task. The finding of the present study provides insights into how humans learn oral motor behaviors or the kind of adaptation that takes place after a successful prosthetic rehabilitation.

Chewing Maintains Hippocampus-Dependent Cognitive Function

Mastication (chewing) is important not only for food intake, but also for preserving and promoting the general health. Recent studies have showed that mastication helps to maintain cognitive functions in the hippocampus, a central nervous system region vital for spatial memory and learning. The purpose of this paper is to review the recent progress of the association between mastication and the hippocampus-dependent cognitive function. There are multiple neural circuits connecting the masticatory organs and the hippocampus. Both animal and human studies indicated that cognitive functioning is influenced by mastication. Masticatory dysfunction is associated with the hippocampal morphological impairments and the hippocampus-dependent spatial memory deficits, especially in elderly. Mastication is an effective behavior for maintaining the hippocampus-dependent cognitive performance, which deteriorates with aging. Therefore, chewing may represent a useful approach in preserving and promoting the hippocampus-dependent cognitive function in older people. We also discussed several possible mechanisms involved in the interaction between mastication and the hippocampal neurogenesis and the future directions for this unique fascinating research.

Spontaneous neural activity alterations in temporomandibular disorders: a cross-sectional and longitudinal resting-state functional magnetic resonance imaging study

The involvement of the central nervous system in the pathophysiology of temporomandibular disorders (TMD) has been noticed. TMD patients have been shown dysfunction of motor performance and reduced cognitive ability in neuropsychological tests. The aim of this study is to explore the spontaneous neural activity in TMD patients with centric relation (CR)-maximum intercuspation (MI) discrepancy before and after stabilization splint treatment. Twenty-three patients and twenty controls underwent clinical evaluations, including CR-MI discrepancy, Helkimo indices and chronic pain, and resting state functional magnetic resonance imaging scans at baseline. Eleven patients repeated the evaluations and scanning after the initial wearing (T1) and 3months of wearing (T2) of the stabilization splint. The fractional amplitude of low-frequency fluctuation (fALFF) was calculated to compare the neural functions. At baseline, the patients showed decreased fALFF in the left precentral gyrus, supplementary motor area, middle frontal gyrus and right orbitofrontal cortex compared with the controls (P<0.05, AlphaSim corrected). Negative correlations were found between the fALFF in the left precentral gyrus and vertical CR-MI discrepancy of bilateral temporomandibular joints of patients (P<0.05, two-tailed). At T2, the symptoms and signs of the patients were improved, and a stable condylar position on the CR was recovered, with increased fALFF in the left precentral gyrus and left posterior insula compared with pretreatment. The fALFF decrease in the patients before treatment was no longer evident at T2 compared with the controls. The results suggested that TMD patients with CR-MI discrepancy showed significantly decreased brain activity in their frontal cortexes. The stabilization splint elicited functional recovery in these cortical areas. These findings provided insight into the cortical neuroplastic processes underlying TMD with CR-MI discrepancy and the therapeutic mechanisms of stabilization splint.

Modulation dynamics in the orofacial sensorimotor cortex during motor skill acquisition

The orofacial sensorimotor cortex is known to play a role in motor learning. However, how motor learning changes the dynamics of neuronal activity and whether these changes differ between orofacial primary motor (MIo) and somatosensory (SIo) cortices remain unknown. To address these questions, we used chronically implanted microelectrode arrays to track learning-induced changes in the activity of simultaneously recorded neurons in MIo and SIo as two naive monkeys (Macaca mulatta) were trained in a novel tongue-protrusion task. Over a period of 8-12 d, the monkeys showed behavioral improvements in task performance that were accompanied by rapid and long-lasting changes in neuronal responses in MIo and SIo occurring in parallel: (1) increases in the proportion of task-modulated neurons, (2) increases in the mutual information between tongue-protrusive force and spiking activity, (3) reductions in the across-trial firing rate variability, and (4) transient increases in coherent firing of neuronal pairs. More importantly, the time-resolved mutual information in MIo and SIo exhibited temporal alignment. While showing parallel changes, MIo neurons exhibited a bimodal distribution of peak correlation lag times between spiking activity and force, whereas SIo neurons showed a unimodal distribution. Moreover, coherent activity between pairs of MIo neurons was higher and centered around force onset compared with pairwise coherence of SIo neurons. Overall, the results suggest that the neuroplasticity in MIo and SIo occurring in parallel serves as a substrate for linking sensation and movement during sensorimotor learning, whereas the differing dynamic organizations reflect specific ways to control movement parameters as learning progresses.

Rethinking Rehab: Skill-Based Training for Swallowing Impairment

Current rehabilitation approaches for swallowing impairment are limited by a general lack of specificity to associated pathophysiology, with many of our practices focusing on increasing strength of muscle activation. However, alternative rehabilitative options are emerging. One of these speculates on the concept of “skill training” for swallowing rehabilitation in neurogenic dysphagia. The presumed intent of this approach is to modulate neural substrates and refine motor planning for swallowing using intrinsically generated cortical modulation and adaptive practice. This manuscript provides a discussion of skill training in the context of physical rehabilitation, illustrating how this information may translate to the diagnosis and remediation of swallowing impairment. This information prompts the consideration of more diverse swallowing pathophysiologies, beyond peripheral muscle weakness. The focus on skill training approaches provides a pathway by which greater specificity of diagnosis and treatment can occur.

Directional information from neuronal ensembles in the primate orofacial sensorimotor cortex

Neurons in the arm and orofacial regions of the sensorimotor cortex in behaving monkeys display directional tuning of their activity during arm reaching and tongue protrusion, respectively. While studies on population activity abound for the arm motor cortex, how populations of neurons from the orofacial sensorimotor cortex represent direction has never been described. We therefore examined and compared the directional information contained in the spiking activity of populations of single neurons recorded simultaneously from chronically implanted microelectrode arrays in the orofacial primary motor (MIo, N = 345) and somatosensory (SIo, N = 336) cortices of monkeys (Macaca mulatta) as they protruded their tongue in different directions. Differential modulation to the direction of tongue protrusion was found in >60% of task-modulated neurons in MIo and SIo and was stronger in SIo (P < 0.05). Moreover, mutual information between direction and spiking was significantly higher in SIo compared with MIo at force onset and force offset (P < 0.01). Finally, the direction of tongue protrusion was accurately predicted on a trial-by-trial basis from the spiking activity of populations of MIo or SIo neurons by using a discrete decoder (P < 0.01). The highly reliable decoding was comparable between MIo and SIo neurons. However, the temporal evolution of the decoding performance differed between these two areas: MIo showed late-onset, fast-rising, and phasic performance, whereas SIo exhibited early-onset, slow-rising, and sustained performance. Overall, the results suggest that both MIo and SIo are highly involved in representing the direction of tongue protrusion but they differ in the amplitude and temporal processing of the directional information distributed across populations of neurons.

Intracortical circuits, sensorimotor integration and plasticity in human motor cortical projections to muscles of the lower face

Previous studies of the cortical control of human facial muscles documented the distribution of corticobulbar projections and the presence of intracortical inhibitory and facilitatory mechanisms. Yet surprisingly, given the importance and precision in control of facial expression, there have been no studies of the afferent modulation of corticobulbar excitability or of the plasticity of synaptic connections in the facial primary motor cortex (face M1). In 25 healthy volunteers, we used standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods to probe motor-evoked potentials (MEPs), short-intracortical inhibition, intracortical facilitation, short-afferent and long-afferent inhibition and paired associative stimulation in relaxed and active depressor anguli oris muscles. Single-pulse TMS evoked bilateral MEPs at rest and during activity that were larger in contralateral muscles, confirming that corticobulbar projection to lower facial muscles is bilateral and asymmetric, with contralateral predominance. Both short-intracortical inhibition and intracortical facilitation were present bilaterally in resting and active conditions. Electrical stimulation of the facial nerve paired with a TMS pulse 5-200 ms later showed no short-afferent inhibition, but long-afferent inhibition was present. Paired associative stimulation tested with an electrical stimulation-TMS interval of 20 ms significantly facilitated MEPs for up to 30 min. The long-term potentiation, evoked for the first time in face M1, demonstrates that excitability of the facial motor cortex is prone to plastic changes after paired associative stimulation. Evaluation of intracortical circuits in both relaxed and active lower facial muscles as well as of plasticity in the facial motor cortex may provide further physiological insight into pathologies affecting the facial motor system.

Distal forelimb representations in primary motor cortex are redistributed after forelimb restriction: a longitudinal study in adult squirrel monkeys

Primary motor cortex (M1) movement representations reflect acquired motor skills. Representations of muscles and joints used in a skilled task expand. However, it is unknown whether motor restriction in healthy individuals results in complementary reductions in M1 representations. With the use of intracortical microstimulation techniques in squirrel monkeys, detailed maps of movement representations in M1 were derived before and up to 35 wk after restriction of the preferred distal forelimb (DFL) by use of a soft cast. Although total DFL area and movement threshold remained constant, casting resulted in a redistribution of digit and wrist/forearm representations. Digit representations progressively decreased, whereas wrist/forearm representations progressively increased in areal extent. In three of four monkeys, hand preference returned to normal by the end of the postcast recovery period, and postrecovery maps demonstrated reversal of restriction-induced changes. However, in one monkey, a chronic motor impairment occurred in the casted limb. Rehabilitation via a forced-use paradigm resulted in recovery in use and skill of the impaired limb, as well as restoration of normal motor maps. These results demonstrate that plasticity in motor representations can be induced by training or restricting movements of the limb. Physiological changes induced by restriction appear to be reversible, even in the case of adverse motor outcomes. The respective contributions of both disuse and lost motor skills are discussed. These results have relevance for clinical conditions requiring forelimb casting as well as interpreting the differential effects of injury and disuse that are necessarily intertwined after cortical injury, as occurs in stroke.

Increased occlusal vertical dimension induces cortical plasticity in the rat face primary motor cortex

Previous studies have demonstrated that functional plasticity in the primary motor cortex (M1) is related to motor-skill learning and changes in the environment. Increased occlusal vertical dimension (iOVD) may modulate mastication, such as in the masticatory cycle, and the firing properties of jaw-muscle spindles. However, little is known about the changes in motor representation within the face primary motor cortex (face-M1) after iOVD. The purpose of the present study was to determine the effect of iOVD on the face-M1 using intracortical microstimulation (ICMS). In an iOVD group, the maxillary molars were built-up by 2mm with acrylic. The electromyographic (EMG) activities from the left (LAD) and right (RAD) anterior digastric (AD), masseter and genioglossus (GG) muscles elicited by ICMS within the right face-M1 were recorded 1, 2 and 8 weeks after iOVD. IOVD was associated with a significant increase in the number of sites within the face-M1 from which ICMS evoked LAD and/or GG EMG activities, as well as a lateral shift in the center of gravity of the RAD and LAD muscles at 1 and 2 weeks, but not at 8 weeks. These findings suggest that a time-dependent neuroplastic change within the rat face-M1 occurs in association with iOVD. This may be related to the animal's ability to adapt to a change in the oral environment.

Time Course of Cortical Plasticity After Facial Nerve Palsy

Background. Functional connectivity is defined as the temporal correlation between spatially remote neurophysiological events. This method has become particularly useful for studying neuroplasticity to detect changes in the collaboration of brain areas during cortical reorganization. Methods. In this article, the authors longitudinally studied voxel-based morphometry and resting state functional magnetic resonance imaging 10 times in 1 patient during the course of Bell palsy (idiopathic facial nerve palsy) up to complete clinical recovery. Results. Morphometric analysis revealed a significant alteration in the face area of the primary motor cortex (M1) contralateral to the paretic face, with an initial increase in gray matter concentration. Functional connectivity analysis between the M1 and other parts of the facial motor network revealed acutely disrupted intrahemispheric connectivity but unaltered interhemispheric connectivity. The disrupted functional connectivity was most pronounced on the day of the onset of symptoms, with a subsequent return toward normal during the course of recovery. This time course was found to differ between the selected parts of the facial motor network. However, the increase in functional connectivity strength preceded clinical recovery in all areas and reached a stable level before the patient fully recovered. Conclusion. These results demonstrate that recovery from facial nerve palsy is complemented by cortical reorganization, with pronounced changes of functional connectivity that precede clinical recovery.

Mechanosensation and maximum bite force in edentulous patients rehabilitated with bimaxillary implant-supported fixed dental prostheses

OBJECTIVE

The aim of this study was to compare tactile sensitivity and maximum voluntary bite force (MBF) of edentulous patients with implant-supported fixed dental prostheses (IFDP/IFDPs) to those wearing complete dentures (CG-CC) and fully dentate subjects (CG-DD).

METHODS

Seven edentulous subjects with IFDP/IFDPs, seven with CG-CC and seven CG-DD, matched for age and gender, participated in the pilot experiments. Three active tactile thresholds (absolute, 50% and 100%) were evaluated by means of copper foils of decreasing thickness (12 foils: 700-5 μm). The passive thresholds were measured in six different sites per quadrant using a custom-made computer-supported strain gauge. MBF was evaluated electronically using the central-bearing point method.

RESULTS

Active tactile thresholds were different between all three groups of dental state (Kruskal-Wallis: absolute P = 0.0156; 50% P = 0.0019; 100% P = 0.0059). The active tactile sensitivity with IFDP/IFDPs was between those of the two other groups, except for the 100% threshold. The median passive tactile threshold was higher in patients with IFDP/IFDPs (5.7 N) than in CG-CC (1.7 N) and CG-DD (0.5 N) (Kruskal-Wallis P < 0.0005). MBF did not differ significantly between the dental states (ns).

CONCLUSION

IFDP/IFDPs are a valuable treatment option for restoring edentulous patients. Limitations concerning their physiological integration into the orofacial system are mainly related to a poor passive rather than active tactile sensitivity or maximum bite force.

Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study

Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. Thirteen healthy, right-handed men, aged 24-35 years (mean age ± SD: 27.3 ± 0.3 years), performed a training task consisting of standardized tongue protrusion onto a force transducer. The tongue task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 h. Functional magnetic resonance imaging was carried out before the tongue-task training (baseline), 1-h after the training, and one-day and one-week follow-up. During scanning, the subjects performed tongue protrusion in blocks interspersed with rest. A region-of-interest (ROI) approach and an explorative search were implemented for the analysis of corticomotor activity across conditions. All subjects completed the tongue-task training (mean success rate 43.0 ± 13.2%). In the baseline condition, tongue protrusion resulted in bilateral activity in regions most typically associated with a motor task including medial frontal gyrus (supplementary motor area [SMA]), precentral gyrus (tongue motor cortex), putamen, thalamus, and cerebellum. The ROI analysis revealed increased activity in the precentral gyrus already 1 h post-training. One day after the training, increased activity was observed in the precentral gyrus, SMA, putamen, and cerebellum. No increase was found 1 week after training. Correlation analyses between changes in success rates and changes in the numbers of voxels showed robust associations for left Area 4a in primary motor cortex 1 h, 1 day, and 1 week after the tongue-task training and for the left Area 4p in primary motor cortex and the left lateral premotor cortex 1 day after the training. In the unrestricted analysis, increased activity was found in the parahippocampal gyrus 1 h after the tongue-task training and remained for a week. Decreased activity was found in right post-central and middle frontal gyri 1 h and 1 week post-training. The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.