Coordinated features in jaw and neck muscle activities induced by chewing of soft and hard gum in healthy subjects.

BACKGROUNDS: Jaw and neck muscles may be activated by chewing load using a hard food. However, it remains unclear how effects the gum hardness to the coordinated features in jaw and neck muscle activities during chewing performance. OBJECTIVES: This study was conducted to quantitatively elucidate the effects of the hardness of the gum on coordinated features in jaw and neck muscle activities using intermuscular EMG-EMG transfer function and EMG-EMG coherence function analyses in 18 healthy subjects. METHODS: Jaw and neck muscle activities were aggregated into the first peak frequency of the power spectrum, and power, gain, phase, and coherence parameters between jaw and neck muscle activities were examined in the first peak frequencies during soft and hard gum chewing. RESULTS: The first peak frequency was not significantly different between soft and hard gum chewing. In contrast, power values of the jaw and neck muscles were significantly increased by chewing of hard gum as compared with soft gum, whereas gain, phase, and coherence were not significantly changed by gum hardness. CONCLUSIONS: The chewing rhythm, the quantitative and temporal coordination, and the functional coordination in jaw and neck muscle activities were not changed during soft and hard gum chewing, as well as increased jaw and neck muscles activities. It is therefore concluded that the chewing rhythmicity and jaw and neck muscles coordination accompanied with the increased jaw and neck muscle activities are maintained under the condition of the chewing load using gum hardness in the healthy individuals.

Activation of Prefrontal Cortex in Process of Oral and Finger Shape Discrimination: fNIRS Study.

BACKGROUND: The differences in the brain activities of the insular and the visual association cortices have been reported between oral and manual stereognosis. However, these results were not conclusive because of the inherent differences in the task performance-related motor sequence conditions. We hypothesized that the involvement of the prefrontal cortex may be different between finger and oral shape discrimination. This study was conducted to clarify temporal changes in prefrontal activities occurring in the processes of oral and finger tactual shape discrimination using prefrontal functional near-infrared spectroscopy (fNIRS). METHODS: Six healthy right-handed males [aged 30.8 ± 8.2 years (mean ± SD)] were enrolled. Measurements of prefrontal activities were performed using a 22-channel fNIRS device (ETG-100, Hitachi Medical Co., Chiba, Japan) during experimental blocks that included resting state (REST), nonsense shape discrimination (SHAM), and shape discrimination (SHAPE). RESULTS: No significant difference was presented with regard to the number of correct answers during trials between oral and finger SHAPE discrimination. Additionally, a statistical difference for the prefrontal fNIRS activity between oral and finger shape discrimination was noted in CH 1. Finger SHAPE, as compared with SHAM, presented a temporally shifting onset and burst in the prefrontal activities from the frontopolar area (FPA) to the orbitofrontal cortex (OFC). In contrast, oral SHAPE as compared with SHAM was shown to be temporally overlapped in the onset and burst of the prefrontal activities in the dorsolateral prefrontal cortex (DLPFC)/FPA/OFC. CONCLUSION: The prefrontal activities temporally shifting from the FPA to the OFC during SHAPE as compared with SHAM may suggest the segregated serial prefrontal processing from the manipulation of a target image to the decision making during the process of finger shape discrimination. In contrast, the temporally overlapped prefrontal activities of the DLPFC/FPA/OFC in the oral SHAPE block may suggest the parallel procession of the repetitive involvement of generation, manipulation, and decision making in order to form a reliable representation of target objects.

Effects of denture wearing on coordinated features of jaw and neck muscle activities during chewing in partially edentulous elderly patients.

PURPOSE: This study was performed to examine how denture wearing improves jaw and neck muscle coordination during chewing in partially edentulous elderly patients. METHODS: Sixteen patients classified as Eichner's index B2 or B3 and 16 young dentate subjects were enrolled. Jaw and neck muscle activities during chewing were recorded using electromyography with and without denture wearing, then analyzed using intermuscular Electromyography (EMG)-EMG transfer and EMG-EMG coherence function analyses to clarify quantitative, temporal, and functional coordination of jaw and neck muscle activities while chewing. Occlusal force and masticatory scores were also determined. RESULTS: Denture wearing increased the power values for jaw closing muscle activities, and improved occlusal area and force, and masticatory score. Gain values for jaw closing and opening muscle activities were decreased in those wearing dentures compared to those not wearing dentures. Denture wearing resulted in equivalent gain values for jaw closing and opening muscle activities as compared to the young subjects. Coherence values for chewing and non-chewing side neck muscle activities were increased as compared to not denture wearing. CONCLUSIONS: The suitability of denture wearing can be evaluated from the viewpoint of gain as a quantitative parameter showing coordination between jaw closing and opening muscle activities. Such evaluation can be performed from the viewpoint of coherence as a parameter of functional coordination between jaw and neck muscle activities during chewing in partially edentulous elderly patients. The gain parameter in regard to jaw muscle activities may be compensated to a state equivalent to that seen in young subjects by wearing an appropriate denture.

Prefrontal modulation during chewing performance in occlusal dysesthesia patients: a functional near-infrared spectroscopy study.

OBJECTIVES: Neuropsychological associations can be considerable in occlusal dysesthesia (OD) patients who routinely complain of persistent occlusal discomfort, and somatization effects in the superior medial prefrontal cortex and the temporal and parietal regions are also present. However, the relationship between physical activity, i.e., chewing, prefrontal cognitive demand, and psychiatric states in OD patients remains unclear. We investigated this relationship in this study. MATERIALS AND METHODS: OD patients (n = 15) and healthy control (n = 15; HC) subjects were enrolled in this study. Occlusal contact, chewing activities of the masticatory muscles, prefrontal activities, and psychiatric states such as depression and somatization, of the participants were evaluated. Functional near-infrared spectroscopy was used to determine prefrontal hemodynamics and the Symptom Checklist-90-R was used to score the psychiatric states. RESULTS: We observed a significant association between prefrontal deactivation during chewing and somatization subscales in OD patients. Further, there were no significant differences with regard to the occlusal state and chewing physical activities between the OD patients and HC subjects. CONCLUSIONS: Chewing-related prefrontal deactivation may be associated with somatization severity in OD patients. CLINICAL RELEVANCE: fNIRS is a functional imaging method that uses the principal of neuro-vascular couplings. It is applicable for evaluation of psychiatric state based on prefrontal cortex blood flow in patients with psychiatric disorders.

Prefrontal Consolidation and Compensation as a Function of Wearing Denture in Partially Edentulous Elderly Patients.

BACKGROUND: The cognitive effects of wearing a denture are not well understood. This study was conducted to clarify the effects of denture use on prefrontal and chewing muscle activities, occlusal state, and subjective chewing ability in partially edentulous elderly individuals. METHODS: A total of 16 partially edentulous patients were enrolled. Chewing-related prefrontal cortex and jaw muscle activities were simultaneously examined using a functional near-infrared spectroscopy (fNIRS) device and electromyography, under the conditions of unwearing, and wearing a denture. Occlusal state and masticatory score were also determined under both conditions. Using multiple linear regression analysis, associations between prefrontal and chewing activities with wearing were examined using change rates. RESULTS: Chewing rhythmicity was maintained under both conditions. As compared with unwearing, the wearing condition was associated with improved prefrontal cortex and chewing muscle activities, occlusal state in regard to force and area, and masticatory score. Also, prefrontal activities were positively associated with burst duration and peak amplitude in masseter (Mm) and temporal muscle activities, as well as masticatory scores. In contrast, prefrontal activities were negatively associated with occlusal force. CONCLUSION: Wearing a denture induced a positive association between burst duration and peak amplitude in Mm and temporal muscle activities and prefrontal activity, which may indicate a parallel consolidation of prefrontal cortex and rhythmical chewing activities, as well as masticatory scores. On the other hand, denture use induced a negative association of occlusal force with prefrontal activities, which might suggest that prefrontal compensative associations for the physiocognitive acquisition depended on biomechanical efficacy gained by wearing a denture.

Improved Prefrontal Activity and Chewing Performance as Function of Wearing Denture in Partially Edentulous Elderly Individuals: Functional Near-Infrared Spectroscopy Study.

The purpose of this study was to elucidate the effects of wearing a denture on prefrontal activity during chewing performance. We specifically examined that activity in 12 elderly edentulous subjects [63.1±6.1 years old (mean ± SD)] and 12 young healthy controls (22.1±2.3 years old) using functional near-infrared spectroscopy (fNIRS) in order to evaluate the quality of prefrontal functionality during chewing performance under the conditions of wearing a denture and tooth loss, and then compared the findings with those of young healthy controls. fNIRS and electromyography were used simultaneously to detect prefrontal and masticatory muscle activities during chewing, while occlusal force and masticatory score were also examined by use of a food intake questionnaire. A significant increase in prefrontal activity was observed during chewing while wearing a denture, which was accompanied by increased masticatory muscle activity, occlusal force, and masticatory score, as compared with the tooth loss condition. Prefrontal activation during chewing while wearing a denture in the elderly subjects was not much different from that in the young controls. In contrast, tooth loss in the elderly group resulted in marked prefrontal deactivation, accompanied by decreased masticatory muscle activity, occlusal force, and masticatory score, as compared with the young controls. We concluded that intrinsic prefrontal activation during chewing with a denture may prevent prefrontal depression induced by tooth loss in elderly edentulous patients.

Evaluation of jaw and neck muscle activities while chewing using EMG-EMG transfer function and EMG-EMG coherence function analyses in healthy subjects.

This study aims to quantitatively clarify the physiological features in rhythmically coordinated jaw and neck muscle EMG activities while chewing gum using EMG-EMG transfer function and EMG-EMG coherence function analyses in 20 healthy subjects. The chewing side masseter muscle EMG signal was used as the reference signal, while the other jaw (non-chewing side masseter muscle, bilateral anterior temporal muscles, and bilateral anterior digastric muscles) and neck muscle (bilateral sternocleidomastoid muscles) EMG signals were used as the examined signals in EMG-EMG transfer function and EMG-EMG coherence function analyses. Chewing-related jaw and neck muscle activities were aggregated in the first peak of the power spectrum in rhythmic chewing. The gain in the peak frequency represented the power relationships between jaw and neck muscle activities during rhythmic chewing. The phase in the peak frequency represented the temporal relationships between the jaw and neck muscle activities, while the non-chewing side neck muscle presented a broad range of distributions across jaw closing and opening phases. Coherence in the peak frequency represented the synergistic features in bilateral jaw closing muscles and chewing side neck muscle activities. The coherence and phase in non-chewing side neck muscle activities exhibited a significant negative correlation. From above, the bilateral coordination between the jaw and neck muscle activities is estimated while chewing when the non-chewing side neck muscle is synchronously activated with the jaw closing muscles, while the unilateral coordination is estimated when the non-chewing side neck muscle is irregularly activated in the jaw opening phase. Thus, the occurrence of bilateral or unilateral coordinated features in the jaw and neck muscle activities may correspond to the phase characteristics in the non-chewing side neck muscle activities during rhythmical chewing. Considering these novel findings in healthy subjects, EMG-EMG transfer function and EMG-EMG coherence function analyses may also be useful to diagnose the pathologically in-coordinated features in jaw and neck muscle activities in temporomandibular disorders and whiplash-associated disorders during critical chewing performance.

Characteristics of middle-aged and older patients with temporomandibular disorders and burning mouth syndrome.

The aim of this study was to evaluate the relationship between pain intensities and psychosocial characteristics in middle-aged and older patients with temporomandibular disorders (TMDs) and burning mouth syndrome (BMS). Subjects were selected according to the Research Diagnostic Criteria for TMD (n = 705) and International Association for the Study of Pain criteria for BMS (n = 175). Patients were then divided into two age groups: 45-64 years (middle-aged, Group A) and 65-84 years (older, Group B). Pain intensity and depression and somatization scores were evaluated in both groups. In BMS patients, present and worst pain intensities were significantly higher in Group B than in Group A {4.6 [95% confidence interval (CI) = 4.0-5.2] vs. 3.5 [95% CI = 3.1-3.9] and 5.9 [95% CI = 5.2-6.4] vs. 5.0 [95% CI = 4.5-5.6], respectively; P < 0.05}, with no difference observed in TMD patients. The depression and somatization scores were significantly higher in Group A than in Group B among BMS patients [0.57 (95% CI = 0.45-0.69) vs. 0.46 (95% CI = 0.34-0.59) and 0.537 (95% CI = 0.45-0.63) vs. 0.45 (95% CI = 0.34-0.55); P < 0.05], with no difference observed in TMD patients. The results of the present study indicate that pain intensities and psychosocial characteristics in BMS appear to differ between middle-aged and older patients.

Does shape discrimination by the mouth activate the parietal and occipital lobes? - near-infrared spectroscopy study.

A cross-modal association between somatosensory tactile sensation and parietal and occipital activities during Braille reading was initially discovered in tests with blind subjects, with sighted and blindfolded healthy subjects used as controls. However, the neural background of oral stereognosis remains unclear. In the present study, we investigated whether the parietal and occipital cortices are activated during shape discrimination by the mouth using functional near-infrared spectroscopy (fNIRS). Following presentation of the test piece shape, a sham discrimination trial without the test pieces induced posterior parietal lobe (BA7), extrastriate cortex (BA18, BA19), and striate cortex (BA17) activation as compared with the rest session, while shape discrimination of the test pieces markedly activated those areas as compared with the rest session. Furthermore, shape discrimination of the test pieces specifically activated the posterior parietal cortex (precuneus/BA7), extrastriate cortex (BA18, 19), and striate cortex (BA17), as compared with sham sessions without a test piece. We concluded that oral tactile sensation is recognized through tactile/visual cross-modal substrates in the parietal and occipital cortices during shape discrimination by the mouth.

Age-related associations between psychological characteristics and pain intensity among Japanese patients with temporomandibular disorder.

We investigated the relationship between pain intensity and psychosocial characteristics in patients with temporomandibular disorder (TMD). Participants with painful TMD, according to the Research Diagnostic Criteria for TMD (RDC/TMD), were recruited from our clinic and classified into six age groups: 15 to 24, 25 to 34, 35 to 44, 45 to 54, 55 to 64, and 65 to 85 years (Groups A through F, respectively). Self-reported present pain intensity and worst pain intensity during the past 6 months were ascertained using a numeric rating scale (0 to 10). Depression and somatization scores were evaluated using the RDC/TMD axis II questionnaire. Among women, worst pain intensity was significantly lower in Groups E and F than in Groups B and C (P < 0.05). In Groups A, C, and D, depression scores were significantly higher in women than in men (P < 0.05). Among women, depression score was significantly lower in Group F than in Groups A through C (P < 0.05). In Groups A through D, somatization scores were significantly higher for women than for men (P < 0.05). Depression score and TMD symptom severity appear to decrease with age in women.

Pain intensity and psychosocial characteristics of patients with burning mouth syndrome and trigeminal neuralgia.

This study compared pain intensity and psychosocial characteristics between patients with burning mouth syndrome (BMS) and those with trigeminal neuralgia (TN). Data from 282 patients with BMS and 83 patients with TN were analyzed. Patients reported duration of illness: duration ≤ 6 months was defined as acute illness and > 6 months as chronic illness. Present pain intensity and worst pain intensity during the past 6 months were reported using a 0-10 numeric rating scale (NRS). In addition, depression and somatization scores were evaluated on questionnaires. Patients with chronic BMS reported significantly higher pain intensity and had worse psychosocial characteristics than did those with acute BMS. Pain intensity was higher in TN patients than in BMS patients, although neither pain intensity nor psychosocial characteristics significantly differed between patients with acute and chronic illness. Logistic regression analysis of BMS and TN patients revealed that the odds ratio for worst pain was significantly lower for BMS patients than for TN patients and that the odds ratio for somatization score was 3.8 times higher in BMS patients. These findings suggest that BMS patients may require pain control targeting the central nervous system or psychosocial characteristics.

Chewing-related prefrontal cortex activation while wearing partial denture prosthesis: pilot study.

PURPOSE: From the standpoint of dental medicine, denture wearing is considered to improve chewing ability, chewing comfort, and quality of life in elderly individuals. We attempted to clarify the effects of prosthodontic treatment on activation of the dorsal prefrontal cortex, which is involved in higher cognitive functions. METHODS: Three partially edentulous patients, one 60-year-old male, and two females, 57 and 64 years old, were enlisted as subjects. For detection of changes in cerebral blood flow, near infrared spectroscopy (NIRS) was used. EMG recording was also conducted to detect bilateral activities of the masseter muscles (Mm). RESULTS: Significant activation of the dorsal prefrontal cortex in the right and/or left hemisphere was shown while wearing partial denture prosthesis. Furthermore, Mm EMG activity was significantly increased while wearing a partial denture prosthesis. CONCLUSIONS: We concluded that a partial dental prosthesis significantly stimulates both masticatory muscle and dorsal prefrontal cortex activities, which might contribute to the prevention of cognitive impairment in aged individuals.

Effects of jaw clenching while wearing an occlusal splint on awareness of tiredness, bite force, and EEG power spectrum.

PURPOSE: Treatment with an occlusal splint is used for temporomandibular disorders, bruxism, and occlusal disturbance to relieve orofacial symptoms such as myofascial pain and jaw movement restriction. However, the effects of various types of occlusal splints have not been elucidated. We investigated the effects of jaw clenching with soft and hard occlusal splints on the awareness of tiredness, bite force, and EEG activity. METHODS: Six healthy adults were used as subjects, with a visual analogue scale utilized to evaluate the awareness of each patient's tiredness both preceding the session and following the clenching trials. In addition, a Dental Prescale was used to measure bite force and an EEG recording was conducted while performing jaw clenching. The jaw clenching task comprised 1min of maximal voluntary clenching under 3 kinds of clenching conditions: with natural dentition, and with soft and hard occlusal splints, which were each repeated 5 times. RESULTS: Jaw clenching with natural dentition and a hard occlusal splint did not cause a significant awareness of tiredness following repetitive jaw clenching, and there was not a significant alteration of EEG spectrum values with those conditions. In contrast, jaw clenching with a soft occlusal splint caused a significant increase in awareness of tiredness, as well as significant decreases in bite force and EEG alpha 2 power spectrum values. CONCLUSIONS: Jaw clenching with a soft resilient occlusal splint causes an awareness of tiredness, which might be accompanied by declines in bite force and EEG spectrum values.

Comparison of occlusal discomfort in patients with temporomandibular disorders between myofascial pain and disc displacement.

We compared occlusal discomfort in patients with temporomandibular disorders (TMD) between myofascial pain (MFP) and disc displacement (DD) using a database created from Sep, 2003 to Aug, 2005. We selected 71 patients with MFP and 170 patients with DD to construct a null model of structural equation modeling (SEM) in which anxiety influenced depressive mood, depressive mood aggravated occlusal discomfort and sleep complaints, and sleep complaints or an onset event caused by another person aggravated occlusal discomfort. We performed a simultaneous analysis of patients with MFP and DD. The estimated parameter of the path from depressive mood to occlusal discomfort was significant for patients with MFP, but not for patients with DD. The path from an onset event caused by another person, such as dental treatment to occlusal discomfort was significant in patients with MFP and those with DD. The Goodness of Fit Index (=0.909), The Adjusted Goodness of Fit Index (=0.867), and The Root Mean Square Error of Approximation (=0.039) indicated good acceptability. These results suggested that an increase in depressive mood may aggravate occlusal discomfort in patients with MFP, and an onset event caused by another person, such as dental treatment, also may aggravate occlusal discomfort in patients with MFP and those with DD.

Plant-specific microtubule-associated protein SPIRAL2 is required for anisotropic growth in Arabidopsis.

In diffusely growing plant cells, cortical microtubules play an important role in regulating the direction of cell expansion. Arabidopsis (Arabidopsis thaliana) spiral2 (spr2) mutant is defective in directional cell elongation and exhibits right-handed helical growth in longitudinally expanding organs such as root, hypocotyl, stem, petiole, and petal. The growth of spr2 roots is more sensitive to microtubule-interacting drugs than is wild-type root growth. The SPR2 gene encodes a plant-specific 94-kD protein containing HEAT-repeat motifs that are implicated in protein-protein interaction. When expressed constitutively, SPR2-green fluorescent protein fusion protein complemented the spr2 mutant phenotype and was localized to cortical microtubules as well as other mitotic microtubule arrays in transgenic plants. Recombinant SPR2 protein directly bound to taxol-stabilized microtubules in vitro. Furthermore, SPR2-specific antibody and mass spectrometry identified a tobacco (Nicotiana tabacum) SPR2 homolog in highly purified microtubule-associated protein fractions from tobacco BY-2 cell cultures. These results suggest that SPR2 is a novel microtubule-associated protein and is required for proper microtubule function involved in anisotropic growth.

Overexpression of a novel small peptide ROTUNDIFOLIA4 decreases cell proliferation and alters leaf shape in Arabidopsis thaliana.

Leaf shape is determined by polar cell expansion and polar cell proliferation along the leaf axes. However, the genes controlling polar cell proliferation during leaf morphogenesis are largely unknown. We identified a dominant mutant of Arabidopsis thaliana, rotundifolia4-1D (rot4-1D), which possessed short leaves and floral organs. We showed that the altered leaf shape is caused by reduced cell proliferation, specifically in the longitudinal (proximal-distal) axis of the leaf, suggesting that the ROT4 gene controls polar cell proliferation in lateral organs. The ROT4 open-reading frame (ORF) encodes a novel small peptide that had not been identified in the Arabidopsis genome annotation. Overexpression of a ROT4-green fluorescence protein (GFP) fusion protein in transgenic plants recapitulated the rot4 phenotype, suggesting that ROT4 acts to restrict cell proliferation. The ROT4-GFP fusion protein localized to the plasma membrane when expressed in transgenic Arabidopsis plants. Phylogenetic analysis indicates that ROT4 defines a novel seed plant-specific family of small peptides with 22 members in Arabidopsis, ROT FOUR LIKE1-22 (RTFL1-22). All RTFL members share a conserved 29-amino acid domain, the RTF domain, and overexpression of the ROT4 RTF domain alone is sufficient to confer a rot4-1D phenotype. Loss-of-function mutations in several RTFL genes were aphenotypic, suggesting that there may be some functional redundancy between family members. Analyses by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization revealed that ROT4 is expressed in the shoot apex and young leaves of wild-type plants, consistent with a role for ROT4 in controlling polarity-dependent cell proliferation during wild-type leaf morphogenesis.

Nuclear medical PET-study in the causal relationship between mastication and brain function in human evolutionary and developmental processes.

The principal author (Kubote 1995, 1997, 1998, 1999, 2000 a, b) has proposed that chewing food well from infancy will lead to a clear-headed and robust person, following which the same concept has been presented to the general public by the mass media. Unfortunately, however, there does not yet seem to be any direct evidence to support this claim. It is thus necessary to review mastication from the standpoint of the new concept of evidence-based medicine (EBM) and to create a new direction in medicodental research and treatment from the viewpoint of human evolution, because the causal relationship between mastication and brain function has never been clarified either in fossil science research or in the modem scientific bibliography. To confirm the human historical fossil record in regard to the causal relationship between the development of mastication and brain function in human evolutionary processes, the effect of gum chewing on brain reaction was examined in humans by means of a positron-emission tomography (PET) camera (Momose et al. 1997) after an antecubital intravenous injection of H215O. Powerful activation of the cortical cells was demonstrated in multiple cortical areas involving the marginal areas of the bilateral central sulci of the cerebral cortex (Fig. 1), and the activated areas coincided with our previous results in region of interest (ROI) analysis (Momose et al. 1887). Three-dimensionally, numerous cortical cells were shown to form nuclei on relief maps (Fig. 2). As diets and feeding habits changed in a stepwise manner from frugivorous to omnivorous via herbivorous and carnivorous over the lengthy progress of evolution, the brain concomitantly grew and the cranial capacity gradually increased in volume from 500 cm3, food from plant sources to animal sources (700 cm3), and then to both (1500 cm3), during the human evolutionary and developmental processes. Gradual increases in the cranial capacity of human fossils during the developmental stage have been demonstrated also by PET images of the human brain acquired by means of a PET camera and an antecubital intravenous injection of H215O during mastication that showed powerful activation of cortical cells in multiple areas. It could be concluded that human fossils give us concrete information on how to feed our children in the modern human life style from infancy to adulthood, so that we should bring children up by adhering to images of the principal feeding habits discovered during this research on human evolutionary and developmental processes.

Effects on mastication of reversible bilateral inactivation of the lateral pericentral cortex in the monkey (Macaca fascicularis).

It is known that intracortical microstimulation (ICMS) of the lateral pericentral cortex can evoke masticatory movements and swallowing in awake monkeys. The aim was to determine if the ability of monkeys to carry out mastication is affected by reversible bilateral cold block of the ICMS-defined cortical masticatory area/swallow cortex. A cranial chamber was implanted bilaterally in two monkeys and a warm or cold alcohol-water solution was pumped through thermodes placed bilaterally on the dura overlying the ICMS-defined cortical masticatory area/swallow cortex while monkeys chewed standardised amounts of fruit during pre-cool (thermode temperature, 37 degrees C), cool (0-4 degrees C), and post-cool (37 degrees C) trials. Electromyographic (EMG) activity was recorded from masseter, genioglossus, anterior digastric, geniohyoid and thyrohyoid or perilaryngeal muscles. Vertical and horizontal jaw movements were recorded with a photodiode position transducer, which monitored movements of a light-emitting diode fixed to the mandible. Each masticatory period was divided into a food-preparatory phase, a rhythmic chewing phase and a preswallow phase. Both monkeys could readily accept and ingest the foodstuffs during pre-cool and post-cool trials. In contrast, cold block was associated with masticatory deficits, reflected in both monkeys as impaired food intake or manipulation and difficulty in carrying out a sequence of masticatory cycles, alterations in of the food-preparatory phase, and alterations in masticatory-related EMG patterns of the jaw and tongue muscles. The cold block-induced changes included significant (P<0.05) prolongations of the total masticatory time, the food-preparatory phase duration, and burst durations of the jaw and tongue muscle EMG activities; furthermore, the amplitudes and temporal correlations of the EMG activities of the jaw and tongue muscles were significantly (P<0.05) changed by cold block. These findings provide further evidence that the lateral pericentral cortex has a critical role in the initiation and regulation of masticatory movements in the primate, and that the programming of masticatory muscle activities may be dependent upon corticofugal influences for engaging masticatory motor activities appropriate to the masticatory conditions.

Effects of reversible bilateral inactivation of face primary motor cortex on mastication and swallowing.

The effects of reversible cold block-induced bilateral inactivation of the face primary motor cortex (face MI) on mastication and swallowing were studied in awake monkeys. A warm or cold alcohol-water solution was pumped through thermodes placed bilaterally on the dura overlying the intracortical microstimulation-defined face MI while the monkey chewed and swallowed food during pre-cool (thermode temperature 37 degrees C), cold block (4 degrees C), and post-cool (37 degrees C) sessions. Vertical and horizontal jaw movements and electromyographic (EMG) activity of several muscles were monitored. Each masticatory sequence was divided into three masticatory phases (i.e. food preparatory, rhythmic chewing, preswallow). The cold block markedly affected the ability of the monkey to carry out mastication although it did not prevent mastication from occurring. The masticatory deficit was characterized by a significant elongation of the total masticatory time, including in particular elongation of the food preparatory phase. The coordination of the jaw- and tongue-muscle activities was severely disrupted during the food preparatory phase. Face MI cold block also significantly affected the duration of some masticatory-related EMG activities and had some limited effects on the temporal relationships of the EMG activities during mastication. Although cold block significantly affected the duration and some EMG parameters of the preswallow phase, it had no significant effect on swallow duration or the EMG parameters during swallowing. These findings provide further evidence that the primate face MI plays a critical role in the regulation of mastication and that it plays a role in the preparation for swallowing.