Rhythmic Jaw Movements Research Articles

Head movements and neck muscle activities associated with the jaw movement during mastication in the rabbit authors

Rhythmical head movements and neck muscle activities associated with the masticatory jaw movement were investigated in rabbits. In natural mastication, head movements and neck muscle activities showed a rhythmical feature synchronized with jaw movement. During cortically induced rhythmical jaw movements, some neck muscle showed rhythmical activity induced by biting a wooden stick. Neck muscles may contribute to the rhythmical head movement after loading the tooth with food.

Direct projections from the magnocellular division of the basal nucleus of the amygdala to the principal part of the cortical masticatory area in the macaque monkey

Direct projections from the amygdala to the cortical masticatory area were found in the macaque monkey. Under the guidance of intracortical microstimulation, retrograde tracers were injected into multiple jaw movement-related regions of the frontal lobe. The cortical masticatory area, especially its principal part, stimulation of which elicited rhythmic jaw movement, was the only site of injection that produced neuronal labeling in the amygdala. The cells of origin of such projections were localized in the medial aspect of the magnocellular division of the basal nucleus through its rostral level. No labeled neurons were observed in the amygdala after tracer injection into any other cortical jaw movement-related region. The present results suggest that the amygdaloid input to the cortical masticatory area may exert some modulatory influence on the generation of masticatory rhythm.

Behavior of jaw muscle spindle afferents during cortically induced rhythmic jaw movements in the anesthetized rabbit.

The regulation by muscle spindles of jaw-closing muscle activity during mastication was evaluated in anesthetized rabbits. Simultaneous records were made of the discharges of muscle spindle units in the mesencephalic trigeminal nucleus, masseter and digastric muscle activity (electromyogram [EMG]), and jaw-movement parameters during cortically induced rhythmic jaw movements. One of three test strips of polyurethane foam, each of a different hardness, was inserted between the opposing molars during the jaw movements. The induced rhythmic jaw movements were crescent shaped and were divided into three phases: jaw-opening, jaw-closing, and power. The firing rate of muscle spindle units during each phase increased after strip application, with a tendency for the spindle discharge to be continuous throughout the entire chewing cycle. However, although the firing rate did not change during the jaw-opening and jaw-closing phases when the strip hardness was altered, the firing rate during the power phase increased in a hardness-dependent manner. In addition, the integrated EMG activity, the duration of the masseteric bursts, and the minimum gape increased with strip hardness. Spindle discharge during the power phase correlated with jaw-closing muscle activity, implying that the change in jaw-closing muscle activity associated with strip hardness was caused by increased spindle discharge produced through insertion of a test strip. The increased firing rate during the other two phases may be involved in a long-latency spindle feedback. This could contribute to matching the spatiotemporal pattern of the central pattern generator to that of the moving jaw.

Features of cortically evoked swallowing in the awake primate (Macaca fascicularis).

Although the cerebral cortex has been implicated in the control of swallowing, the output organization of the cortical swallowing representation, and features of cortically evoked swallowing, remain unclear. The present study defined the output features of the primate "cortical swallowing representation" with intracortical microstimulation (ICMS) applied within the lateral sensorimotor cortex. In four hemispheres of two awake monkeys, microelectrode penetrations were made at </=1-mm intervals, initially within the face primary motor cortex (face-MI), and subsequently within the cortical regions immediately rostral, lateral, and caudal to MI. Two ICMS pulse trains [35-ms train, 0.2-ms pulses at 333 Hz, </=30 microA (short train stimulus, T/S); 3- to 4-s train, 0.2-ms pulses at 50 Hz, </=60 microA (continuous stimulus, C/S)] were applied at </=500-micron intervals along each microelectrode penetration to a depth of 8-10 mm, and electromyographic (EMG) activity was recorded simultaneously from various orofacial and laryngeal muscles. Evoked orofacial movements, including swallowing, were verified by EMG analysis, and T/S and C/S movement thresholds were determined. Effects of varying ICMS intensity on swallow-related EMG properties were examined by applying suprathreshold C/S at selected intracortical sites. EMG patterns of swallows evoked from various cortical regions were compared with those of natural swallows recorded as the monkeys swallowed liquid and solid material. Results indicated that swallowing was evoked by C/S at approximately 20% of 1,569 intracortical sites where ICMS elicited an orofacial motor response in both hemispheres of the two monkeys, typically at C/S intensities </=30 microA. In contrast, swallowing was not evoked by T/S in either monkey. Swallowing was evoked from four cortical regions: the ICMS-defined face-MI, the face primary somatosensory cortex (face-SI), the region lateral and anterior to face-MI corresponding to the cortical masticatory area (CMA), and an area >5 mm deep to the cortical surface corresponding to both the white matter underlying the CMA and the frontal operculum; EMG patterns of swallows elicited from these four cortical regions showed some statistically significant differences. Whereas swallowing ONLY was evoked at some sites, particularly within the deep cortical area, swallowing was more frequently evoked together with other orofacial responses including rhythmic jaw movements. Increasing ICMS intensity increased the magnitude, and decreased the latency, of the swallow-related EMG burst in the genioglossus muscle at some sites. These findings suggest that a number of distinct cortical foci may participate in the initiation and modulation of the swallowing synergy as well as in integrating the swallow within the masticatory sequence.

Scopolamine disruption of behavioral and hippocampal responses in appetitive trace classical conditioning

Twelve young rabbits (3–6 months; Oryctolagus cuniculus) were classically conditioned in a trace jaw movement paradigm (300 ms tone, 450 ms trace, 200 ms intraoral water) after implantation of electrodes into area CA1 of dorsal hippocampus. Rabbits were divided into two groups and administered either 0.5 mg/kg scopolamine hydrobromide (HBr) or 0.5 mg/kg scopolamine methylbromide (MBr) subcutaneously before daily training sessions. Rabbits given HBr took significantly more trials to reach a behavioral criterion of eight conditioned responses in any nine consecutive trials than rabbits given MBr ( P=0.03). Conditioned, but not unconditioned, rhythmic jaw movement responses of the HBr group were of a lower frequency (Hz) than those of MBr rabbits ( P=0.02). The magnitude of hippocampal conditioning-related responses across the first 3 days of training was significantly smaller for HBr rabbits than for MBr rabbits ( P=0.02). These effects of central cholinergic blockade are similar to those reported for undrugged aging rabbits trained in the same paradigm (Seager MA, Borgnis RL, Berry SD. Neurobiol. Aging 1997;18(6):631–639).

Regulation of Intrinsic and Synaptic Properties of Neonatal Rat Trigeminal Motoneurons by Metabotropic Glutamate Receptors

We studied how metabotropic glutamate receptor (mGluR) activation modifies the synaptic and intrinsic membrane properties of neonatal rat trigeminal motoneurons using the broad-spectrum mGluR agonist (1S,3R)-1-amino-1,3-cyclopentane-dicarboxylic acid [(1S,3R)-ACPD], group I/II antagonist (+/-)-alpha-methyl-4-carboxy-phenylglycine (MCPG), and group III agonist L-2-amino-4-phosphonobutanoate (L-AP4). (1S,3R)-ACPD depressed excitatory transmission to trigeminal motoneurons presynaptically and postsynaptically via presynaptic inhibition and by reducing the currents carried by ionotropic glutamate receptors selective for AMPA. (1S,3R)-ACPD also depolarized trigeminal motoneurons and increased input resistance by suppressing a Ba2+-sensitive leakage K+ current. These effects were not mimicked by L-AP4 (100-200 microM). High-threshold Ca2+ currents were also suppressed by (1S,3R)-ACPD. Repetitive stimulation of excitatory premotoneurons mimicked the postsynaptic effects of (1S, 3R)-ACPD. The postsynaptic effects of (1S,3R)-ACPD and repetitive stimulation were both antagonized by MCPG, suggesting that mGluRs were similarly activated in both experiments. We conclude that mGluRs can be recruited endogenously by glutamatergic premotoneurons and that mGluR-mediated depression of excitatory transmission, combined with increased postsynaptic excitability, enhances the signal-to-noise ratio of oral-related synaptic input to trigeminal motoneurons during rhythmical jaw movements.

Intermittency in Mastication and Apomorphine-Induced Gnawing

Rhythmic behaviors like mastication, gnawing, and locomotion, are characterized by temporal segmentation or intermittency. That is, they frequently occur as a series of short bursts interrupted by pauses rather than as one long uninterrupted burst. The function of intermittency as well as the mechanisms that produce it are unknown. Biogenic amine systems may play a role in producing intermittency; however, experimental work to confirm this is only in its infancy. The current study evaluates the structure of intermittency associated with mastication and apomorphine-induced gnawing in the guinea pig. Thirteen free-roaming animals were videotaped while masticating or gnawing. Eight animals were given 0.5 mg/kg i.m. apomorphine and videotaped while gnawing. The remaining five animals received no apomorphine injections, but were taped while feeding on alfalfa pellets. Custom software was used to score instances of maximum jaw closures in videotaped mastication and gnawing sequences. The time between successive maximum jaw closures, called the interocclude interval (IOI), was calculated for all scored sequences. A cutoff IOI value of 0.26 s differentiated pauses (IOI values equal or greater than 0.26 s) from chews or gnaws (IOI values less than 0.26 s). Two or more successive chews or gnaws, without intervening pauses, defined behavior bursts. Chew, gnaw, and burst durations were quantified and compared. Chew and gnaw durations were similar. However, chewing bursts were significantly longer than gnawing bursts. The significance of these results is presented in light of previous neurophysiological work on rhythmic jaw movements and intermittency.

Evidence that Trigeminal Brainstem Interneurons Form Subpopulations to Produce Different Forms of Mastication in the Rabbit

To determine how trigeminal brainstem interneurons pattern different forms of rhythmical jaw movements, four types of motor patterns were induced by electrical stimulation within the cortical masticatory areas of rabbits. After these were recorded, animals were paralyzed and fictive motor output was recorded with an extracellular microelectrode in the trigeminal motor nucleus. A second electrode was used to record from interneurons within the lateral part of the parvocellular reticular formation (Rpc-alpha, n = 28) and gamma- subnucleus of the oral nucleus of the spinal trigeminal tract (NVspo-gamma, n = 68). Both of these areas contain many interneurons projecting to the trigeminal motor nucleus. The basic characteristics of the four movement types evoked before paralysis were similar to those seen after the neuromuscular blockade, although cycle duration was significantly decreased for all patterns. Interneurons showed three types of firing pattern: 54% were inactive, 42% were rhythmically active, and 4% had a tonic firing pattern. Neurons within the first two categories were intermingled in Rpc-alpha and NVspo-gamma: 48% of rhythmic neurons were active during one movement type, 35% were active during two, and 13% were active during three or four patterns. Most units fired during either the middle of the masseter burst or interburst phases during fictive movements evoked from the left caudal cortex. In contrast, there were no tendencies toward a preferred coupling of interneuron activity to any particular phase of the cycle during stimulation of other cortical sites. It was concluded that the premotoneurons that form the final commands to trigeminal motoneurons are organized into subpopulations according to movement pattern.

Effects on non-human primate mastication of reversible inactivation by cooling of the face primary somatosensory cortex

Rhythmical jaw movements can be evoked by intracortical microstimulation within four physiologically defined regions, one of which is the primary face somatosensory cortex (face SI). It has been proposed that these regions may be involved in the selection and/or control of masticatory patterns generated at the brainstem level. The aim here was to determine if mastication is affected by reversible, cooling-induced inactivation of the face SI. Two cranial chambers were chronically implanted in two monkeys ( Macaca fascicularis) to allow access bilaterally to the face SI. A thermode was placed on the dura or pia overlying each SI that had been shown with micro-electrode recordings to receive intraoral inputs. A hot or cold alcohol–water solution was pumped through the thermodes while the monkey chewed a small piece of apple or a sultana during precool (thermode temperature, 37°C), cool (2–4°C), and postcool (37°C) conditions. Electromyographic (EMG) activity was recorded intramuscularly from the masseter, genioglossus, and anterior digastric. Cooling of SI impaired rhythmical jaw and tongue movements and EMG activity associated with mastication in one monkey (H5), and modified the pattern of EMG activity in the other (H6). The total masticatory time (i.e., time taken for chewing and manipulation of the bolus before swallowing) was increased. This was due principally to an increase in the oral transport time (i.e., time taken for manipulation of bolus after chewing and before swallowing: monkey H6, control, 2.7 sec; cool, 5.2 sec, p<0.05); the bolus was manipulated by the tongue during this period before swallowing. Within the chewing time (i.e., time during which chewing occurred), cooling resulted in a significant increase in anterior digastric muscle duration, a significant delay in the onset of masseter EMG activity, and a significant increase in the variance of genioglossus EMG duration. The data support the view that the face SI plays a part in modulating the central pattern generator for mastication.

Patterned jaw movements and the motor neuron activity during rejection of seaweed in Aplysia kurodai

Japanese Aplysia kurodai feeds well on Ulva. In the present experiments we collected several species of seaweed at a location with many animals and initially explored the preference behavior for them. The animals rejected Grateloupia, Pachydictyon, Gelidium and Laurencia with rhythmic jaw and radula movements (active rejection). The animals sometimes bit off a piece of them (biting-off response). Recording activity of muscles contributing to jaw-opening and jaw-closing in freely moving animals showed that the onset of the jaw-closing activity, which always started later than the jaw-opening activity during each cycle of ingestion of Ulva, was advanced toward that of the jaw-opening activity during each cycle of the active rejection. Semi-intact experiments also showed that application of Pachydictyon or Gelidium extract to the lip region advanced the firing onset of the jaw-closing motor neurons at the radula-retraction phase. Video analysis showed that during the Ulva response the jaws opened at the radula-protraction phase and remained half-open at the earlier radula-retraction phase, while the jaws opened similarly at the radula-protraction phase but immediately closed at the radula-retraction phase during the Pachydictyon or Gelidium response.

Neuronal activity related to spontaneous and capsaicin-induced rhythmical jaw movements in the rat.

Intraoral capsaicin induced rhythmical jaw movements (RJM) in anesthetized rats. Neurons in the trigeminal spinal nucleus caudalis or the cortico-peduncular (CP) axons were extracellularly recorded. Capsaicin excited dose-dependently most caudalis neurons, which were activated by stimulation of the oral cavity and/or the tooth pulp and activated during spontaneous or induced RJM. Ten of 55 CP axons were antidromically activated by stimulation of the contralateral trigeminal motor nucleus. All antidromic and 29 other CP axons discharged prior to the spontaneous RJM, but most of them did not during capsaicin-induced RJM. These neuronal activities possibly initiate spontaneous RJM although the activities of caudalis neurons are necessary for capsicin-induced RJM.

Examination of the relationships between jaw opener and closer rhythmical muscle activity in an in vitro brainstem jaw-attached preparation

An in vitro jaw-attached brainstem preparation was developed to investigate the relationship between jaw opener and closer muscle activity during chemically induced rhythmical jaw movements in neonatal rats. In the majority of preparations examined, where a defined region of brainstem was isolated and the neuronal innervation of the jaw opener and closer muscles was left intact, bath application of the excitatory amino acid agonist N -methyl-D,L-aspartate (NMA, 20-40 muM) in combination with bicuculline (BIC 10 muM), a GABAA antagonist, produced rhythmical electromyogram (EMG) activity in jaw opener and closer muscles, bilaterally, in conjunction with rhythmical jaw movements. Low concentrations of NMA (20 muM) in combination with BIC produced temporally coordinated activity between the jaw opener and closer muscles, ipsilaterally. With higher doses of NMA (40 muM), each muscle group exhibited bursting, but temporal coordination between them was difficult to establish. Similarly, NMA application in combination with the glycine antagonist strychnine (STR, 10 muM), also produced rhythmical EMG activity from both opener and closer muscles, ipsilaterally, but showed no temporal coordination between the antagonist muscle pair. However, coordination of opener and closer muscle discharge could be restored by the addition of BIC to the bath. We suggest that there exist separate, but coordinated, rhythm generator circuits for opener and closer motoneuronal discharge located in close proximity to the trigeminal motor nucleus and under GABAergic control for production of temporal coordination between rhythmogenic circuits.

Regulation of masticatory force during cortically induced rhythmic jaw movements in the anesthetized rabbit.

To examine the relationships between masticatory force, electromyogram (EMG) of masticatory muscles, and jaw movement pattern, we quantitatively evaluated the effects of changing hardness of a chewing substance on these three variables. Cortically induced rhythmic jaw movements of a crescent-shaped pattern were induced by electrical stimulation of the cerebral cortical masticatory area in the anesthetized rabbit. The axially directed masticatory force was recorded with a small force-displacement transducer mounted on the ground surface of the lower molars. EMGs were recorded from the masseter and digastric muscles simultaneously with jaw movements. Five test strips of polyurethane foam of different hardness were prepared and inserted between the upper molar and the transducer during the movements. The peak, impulse, and buildup speed of the masticatory force increased with strip hardness, whereas duration of the exerted force did not vary with strip hardness. The integrated activity and duration of the masseteric EMG bursts also increased with strip hardness. The integrated EMG activity of the digastric bursts was weakly related to strip hardness, whereas the duration was not. The minimum gape increased with strip hardness, but the maximum gape did not. The horizontal excursion of the jaw did not vary in a hardness-dependent manner, although it was greater in the cycles with strip application than in the cycles without strip application. Deprivation of periodontal sensation by cutting the nerves to the teeth reduced the buildup speed of the force, maximum gape, net gape, and horizontal jaw movements. The denervation also elongated the force duration and that of masseteric EMG bursts. However, the rate of the hardness-dependent changes in the above parameters did not alter after denervation. The latency of the masseteric EMG response to strip application was evaluated before and after denervation. In both conditions, it was > or = 6 ms in approximately 70% of the cycles and <6 ms in the remaining approximately 30%, which cannot be explained by a simple reflex mechanism. On the basis of the analysis of correlation coefficients, the masseteric integrated EMG seemed to be a good indicator of the peak and impulse of the masticatory force both before and after denervation. We conclude that periodontal afferents would be responsible for a quick buildup of masticatory force and that afferents other than those from periodontal tissue would contribute to the hardness-dependent change of masticatory force during cortically induced rhythmic jaw movements.

Activity of the orbicularis oris during rhythmical jaw movements in freely moving rats

Activity of the orbicularis oris during rhythmical jaw movements in freely moving rats

2006 Activity of the orbicularis oris during rhythmical jaw movements in freely moving rats

2006 Activity of the orbicularis oris during rhythmical jaw movements in freely moving rats

EMG analysis of rhythmical jaw movement with respect to trigeminal activity: Using a jaw-attached isolated brainstem preparation in vitro

EMG analysis of rhythmical jaw movement with respect to trigeminal activity: Using a jaw-attached isolated brainstem preparation in vitro

Modulation of human rhythmical jaw motor function by perioral argon laser stimuli

The influence of peripheral afferent activity on human jaw motor function was examined in this study. Painful argon laser stimuli were applied to the upper lip in 10 subjects during rhythmical jaw movements and the effects on the jaw-closer electromyogram (EMG) and jaw movements were studied. The duration of the open-close cycle (1 sec) and the voluntary level of the jaw-closer EMG burst were standardized by auditory and visual feedback, respectively. Laser stimuli (0.2 sec) were delivered at predetermined percentages of the open-close cycle. Laser stimulation consistently had an excitatory effect on the jaw-closer EMG burst. The root-mean-square (RMS) value of the stimulus-related EMG burst was significantly larger than the preceding and the following EMG bursts. The excitatory effects on the jaw-closer EMG burst were modulated with respect to where in the open-close cycle the laser stimulus was applied, the voluntary force of the jaw-closer burst, and the laser stimulus intensity. Thus, the largest excitatory effects were seen during the start of jaw closure, with the most forceful voluntary contractions, and with the most painful laser stimuli. The stimulus-related changes in the jaw-closer EMG bursts were always associated with a significant shortening (30–90 msec) of the duration of the open-close cycle. The present results suggest that argon laser-induced activity in sensory afferents may generally have an excitatory effect on rhythmical jaw-closer motor performance.

Depression of reciprocal Ia inhibition of crural motoneurons during rhythmical jaw movement in rabbit

The purpose of this study was to investigate how the reciprocal inhibition of the ankle-flexor motoneuron by the ankle-extensor spindle afferents is altered during cortically-induced rhythmical jaw movement (RJM) in urethane-anesthetized rabbit. The monosynaptic reflex (MSR) was induced by test shock of the common peroneal nerve (CPN) and recorded from a distal point of the nerve. The conditioning shock applied to the tibial nerve (TN) at the intensity below 1.2 times the threshold caused a significant inhibition of the MSR in the CPN. The inhibition tended to slightly decrease with an increase in amplitude of the test MSR with either application of stronger test shock or during RJM. The decrease of the reciprocal inhibition significantly exceeded the degree that can be ascribed to the increase of the amplitude of the MSR during RJM. The reciprocal inhibition was significantly reduced during fictive as well as actual RJM. It was concluded that (1) the reciprocal Ia inhibition of the crural motoneurons in the rabbit is reduced with RJM and (2) the intraoral sensory input is not essential for this reduction. This study indicated that the oral motor activity generally exerts a strong influence on the bodily motor function.

Modification of rhythmical jaw movements by noxious pressure applied to the periosteum of the zygoma in decerebrate rabbits

The purpose of this study was to describe and quantify changes in the movement and EMG patterns caused by tonic noxious pressure On the periosteum of the zygoma during electrically induced rhythmic jaw movements in the decerebrate rabbit. Eight New Zealand rabbits were anesthetized with urethane. EMG electrodes were placed in the masseter and digastric muscles and a light was attached to the mandibular symphysis to track jaw movements. The animals were decerebrated and the anesthetic was discontinued. Rhythmic jaw movements were evoked by electrically stimulating the corticobulbar tracts (1-msec rectangular pulses, 50 Hz), in the absence and presence Of tonic noxious pressure applied bilaterally to the zygomatic periosteum (range: 400–1500 kPa). The overall response to tonic noxious pressure was a statistically significant decrease in the frequency and amplitude of the rhythmic jaw movements and in the mandibular velocity during opening and closing. The slowing of the frequency was associated with a significant increase in the duration between muscle bursts. In those animals in which the jaw closing muscles were most active, there was a significant decrease in the area of the masseter muscle bursts during jaw closure. The changes in motor activity in response to the application of tonic noxious pressure are similar to those that have been reported for patients experiencing musculoskeletal pain, suggesting that pain modifies motor programs at the segmental level. Our data support the pain-adaptation model.

Characteristics of a fast transient outward current in guinea pig trigeminal motoneurons

A fast transient voltage dependent outward current (TOC) in trigeminal motoneurons (TMNs) was studied in guinea pig brainstem slices by use of sharp electrodes in combination with single electrode voltage clamp techniques. In solutions containing TTX, low Ca 2+Mn 2+ and 20 mM TEA this current activated around −55 to −60 mV from holding potentials negative to resting potential, obtained its peak amplitude within 5 ms and decayed as a single exponential with a time constant of 6–8 ms. Half maximal values for inactivation and activation were −72 and −37 mV, respectively. Bath application of 5mM 4-AP suppressed this current by approximately 90% and eliminated the early depolarizing transient membrane rectification observed in response to a constant depolarizing current pulse, prolonged the action potential duration, and reduced the threshold voltage and delay to onset of the action potential. It is suggested that this current resembles the typical A-current observed in many CNS neurons and, as a result of its voltage and time dependent properties, could contribute to control of motoneuronal discharge and timing of burst onset during rhythmical jaw movements. Therefore, any cellular models of masticatory activity should include the properties of this current.