Genioglossus Electromyographic Research Articles

Task-dependent neural control of regions within human genioglossus.

Anatomical and imaging evidence suggests neural control of oblique and horizontal compartments of the genioglossus differs. However, neurophysiological evidence for differential control remains elusive. This study aimed to determine whether there are differences in neural drive to the oblique and horizontal regions of the genioglossus during swallowing and tongue protrusion. Adult participants (n = 63; 48 M) were recruited from a sleep clinic; 41 had obstructive sleep apnea (OSA: 34 M, 8 F). Electromyographic (EMG) was recorded at rest (awake, supine) using four intramuscular fine-wire electrodes inserted percutaneously into the anterior oblique, posterior oblique, anterior horizontal, and posterior horizontal genioglossus. Epiglottic pressure and nasal airflow were also measured. During swallowing, two distinct EMG patterns were observed - a monophasic response (single EMG peak) and a biphasic response (2 bursts of EMG). Peak EMG and timing of the peak relative to epiglottic pressure were significantly different between patterns (linear mixed models, P < 0.001). Monophasic activation was more likely in the horizontal than oblique region during swallowing (OR = 6.83, CI = 3.46-13.53, P < 0.001). In contrast, during tongue protrusion, activation patterns and EMG magnitude were not different between regions. There were no systematic differences in EMG patterns during swallowing or tongue protrusion between OSA and non-OSA groups. These findings provide evidence for functional differences in the motoneuronal output to the oblique and horizontal compartments, enabling differential task-specific drive. Given this, it is important to identify the compartment from which EMG is acquired. We propose that the EMG patterns during swallowing may be used to identify the compartment where a recording electrode is located.NEW & NOTEWORTHY During swallowing, we observed two distinct, stereotyped muscle activation patterns that define the horizontal (monophasic, maximal EMG) and oblique (biphasic, submaximal EMG) neuromuscular compartments of genioglossus. In contrast, volitional tongue protrusions produced uniform activation across compartments. This provides evidence for task-dependent, functionally discrete neuromuscular control of the oblique and horizontal compartments of genioglossus. The magnitude and temporal patterning of genioglossus EMG during swallowing may help guide electrode placement in tongue EMG studies.

Changes in pharyngeal collapsibility and genioglossus reflex responses to negative pressure during the respiratory cycle in obstructive sleep apnoea.

Impaired pharyngeal anatomy and increased airway collapsibility is a major cause of obstructive sleep apnoea (OSA) and a mediator of its severity. Upper airway reflexes to changes in airway pressure provide important protection against airway closure. This study shows increased pharyngeal collapsibility and attenuated genioglossus reflex responses during expiration in people with OSA. Upper airway collapse contributes to obstructive sleep apnoea (OSA) pathogenesis. Pharyngeal dilator muscle activity varies throughout the respiratory cycle and may contribute to dynamic changes in pharyngeal collapsibility. However, whether upper airway collapsibility and reflex responses to changes in airway pressure vary throughout the respiratory cycle in OSA is unclear. Thus, this study quantified differences in upper airway collapsibility and genioglossus electromyographic (EMG) activity and reflex responses during different phases of the respiratory cycle. Twelve middle-aged people with OSA (2 female) were fitted with standard polysomnography equipment: a nasal mask, pneumotachograph, two fine-wire intramuscular electrodes into the genioglossus, and a pressure catheter positioned at the epiglottis and a second at the choanae (the collapsible portion of the upper airway). At least 20 brief (∼250ms) pressure pulses (∼-11cmH2 O at the mask) were delivered every 2-10 breaths during four conditions: (1) early inspiration, (2) mid-inspiration, (3) early expiration, and (4) mid-expiration. Mean baseline genioglossus EMG activity 100ms prior to pulse delivery and genioglossus reflex responses were quantified for each condition. The upper airway collapsibility index (UACI), quantified as 100×(nadir choanal - epiglottic pressure)/nadir choanal pressure during negative pressure pulses, varied throughout the respiratory cycle (early inspiration=43±25%, mid-inspiration=29±19%, early expiration=83±19% and mid-expiration=95±11% (mean±SD) P<0.01). Genioglossus EMG activity was lower during expiration (e.g. mid-expiration vs. mid-inspiration=76±23vs. 127±41% of early-inspiration, P<0.001). Similarly, genioglossus reflex excitation was delayed (39±11vs. 23±7ms, P<0.001) and reflex excitation amplitude attenuated during mid-expiration versus early inspiration (209±36vs. 286±80%, P=0.009). These findings may provide insight into the physiological mechanisms of pharyngeal collapse in OSA.

0068 Effect of Tongue Motor Task Training on Serotonergic Excitatory Drive to Genioglossus Electromyographic Activity in Rats

0068 Effect of Tongue Motor Task Training on Serotonergic Excitatory Drive to Genioglossus Electromyographic Activity in Rats

Effect of head and jaw position on respiratory-related motion of the genioglossus.

Head and jaw position influence upper airway patency and electromyographic (EMG) activity of the main upper airway dilator muscle, the genioglossus. However, it is not known whether changes in genioglossus EMG activity translate into altered muscle movement during respiration. The aim of this study was to determine the influence of head and jaw position on dilatory motion of the genioglossus in healthy adult men during quiet breathing by measuring the displacement of the posterior tongue in six positions--neutral, head extension, head rotation, head flexion, mouth opening, and mandibular advancement. Respiratory-related motion of the genioglossus was imaged with spatial modulation of magnetization (SPAMM) in 12 awake male participants. Tissue displacement was quantified with harmonic phase (HARP) analysis. The genioglossus moved anteriorly beginning immediately before or during inspiration, and there was greater movement in the oropharynx than in the velopharynx in all positions. Anterior displacements of the oropharyngeal tongue varied between neutral head position (0.81 ± 0.41 mm), head flexion (0.62 ± 0.45 mm), extension (0.39 ± 0.19 mm), axial rotation (0.39 ± 0.2 mm), mouth open (1.24 ± 0.72 mm), and mandibular advancement (1.08 ± 0.65 mm). Anteroposterior displacement increased in the mouth-open position and decreased in the rotated position relative to cross-sectional area (CSA) (P = 0.002 and 0.02, respectively), but CSA did not independently predict anteroposterior movement overall (P = 0.057). The findings of this study suggest that head position influences airway dilation during inspiration and may contribute to variation in airway patency in different head positions.

Common drive to the upper airway muscle genioglossus during inspiratory loading.

Common drive is thought to constitute a central mechanism by which the efficiency of a motor neuron pool is increased. This study tested the hypothesis that common drive to the upper airway muscle genioglossus (GG) would increase with increased respiratory drive in response to an inspiratory load. Respiration, GG electromyographic (EMG) activity, single-motor unit activity, and coherence in the 0-5 Hz range between pairs of GG motor units were assessed for the 30 s before an inspiratory load, the first and second 30 s of the load, and the 30 s after the load. Twelve of twenty young, healthy male subjects provided usable data, yielding 77 pairs of motor units: 2 Inspiratory Phasic, 39 Inspiratory Tonic, 15 Expiratory Tonic, and 21 Tonic. Respiratory and GG inspiratory activity significantly increased during the loads and returned to preload levels during the postload periods (all showed significant quadratic functions over load trials, P < 0.05). As hypothesized, common drive increased during the load in inspiratory modulated motor units to a greater extent than in expiratory/tonic motor units (significant load × discharge pattern interaction, P < 0.05). Furthermore, this effect persisted during the postload period. In conclusion, common drive to inspiratory modulated motor units was elevated in response to increased respiratory drive. The postload elevation in common drive was suggestive of a poststimulus activation effect.

A comprehensive assessment of genioglossus electromyographic activity in healthy adults.

The genioglossus (GG) is an extrinsic muscle of the human tongue that plays a critical role in preserving airway patency. In the last quarter century, >50 studies have reported on respiratory-related GG electromyographic (EMG) activity in human subjects. Remarkably, of the studies performed, none have duplicated subject body position, electrode recording locations, and/or breathing task(s), making interpretation and integration of the results across studies extremely challenging. In addition, more recent research assessing lingual anatomy and muscle contractile properties has identified regional differences in muscle fiber type and myosin heavy chain expression, giving rise to the possibility that the anterior and posterior regions of the muscle fulfill distinct functions. Here, we assessed EMG activity in anterior and posterior regions of the GG, across upright and supine, in rest breathing and in volitionally modulated breathing tasks. We tested the hypotheses that GG EMG is greater in the posterior region and in supine, except when breathing is subject to volitional modulation. Our results show differences in the magnitude of EMG (%regional maximum) between anterior and posterior muscle regions (7.95 ± 0.57 vs. 11.10 ± 0.99, respectively; P < 0.001), and between upright and supine (8.63 ± 0.73 vs. 10.42 ± 0.90, respectively; P = 0.008). Although the nature of a task affects the magnitude of EMG (P < 0.001), the effect is similar for anterior and posterior muscle regions and across upright and supine (P > 0.2).

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.

Human hypoglossal motor unit activities in exercise

The genioglossus (GG) muscle is considered the principal protruder muscle of the tongue that dilates and stiffens the pharyngeal airway. We recorded whole muscle and single motor unit (MU) activities in healthy adults performing progressive intensity exercise on a cycle ergometer. Tungsten microelectrodes were inserted percutaneously into the GG of 11 subjects (20-40 years) to record electromyographic (EMG) activities and pulmonary ventilation (VI) at rest and at workload increments up to 300 W. Increases in respiratory drive were associated with increases in VI, mean inspiratory flow (Vt/Ti) and tonic and phasic components of the GG EMG activity. In contrast, individual MUs typically showed expiration-related decreases in firing as exercise intensity increased. We suggest the decrease in MU activity may occur secondary to afferent feedback from lungs/chest wall and that compensation for more negative inspiratory airway pressures generated during heavy exercise occurs primarily via recruitment of previously silent MUs.

Single motor unit activity in the genioglossus muscle during vowel articulation

There is an abundance of previous electromyographic (EMG) research conducted in the human tongue that has as its focus the extrinsic tongue muscle, genioglossus (GG) and its role in preserving upper airway patency for purposes of gas exchange. Comparatively few studies have documented GG EMG activities in the performance of volitional tasks such as speech production (Honda 1992; Honda et al. 1992; Kusakawa et al 1993). Here we report on de novo efforts to characterize GG single motor unit (SMU) activities in the context of volitional i.e., speech and automatic i.e., central pattern generator driven respiratory activities. Using tungsten microelectrodes inserted into the belly of the GG in 5 healthy adults, we recorded SMU activity during static articulation of the vowels [a] and [ae] in three conditions: phonated, whispered, and articulation using an electrolarynx. Preliminary findings provide evidence of recruitment and de-recruitment of GG motor units coincident with the onset and offset of vowel articulation in phonated and whispered, but not electrolarynx conditions. Furthermore, fluctuations in GG MU firing rates mirror intensity variations within phonated and whispered utterances. These findings provide much-needed new insights into the differential modulation of lingual motor unit activities for purposes of speech production versus breathing.

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.

Neurogenic Changes in the Upper Airway of Patients with Obstructive Sleep Apnea

Controversy persists regarding the presence and importance of hypoglossal nerve dysfunction in obstructive sleep apnea (OSA). We assessed quantitative parameters related to motor unit potential (MUP) morphology derived from electromyographic (EMG) signals in patients with OSA versus control subjects and hypothesized that signs of neurogenic remodeling would be present in the patients with OSA. Participants underwent diagnostic sleep studies to obtain apnea-hypopnea indices. Muscle activity was detected with 50-mm concentric needle electrodes. The concentric needle was positioned at more than 10 independent sites per subject, after the local anatomy of the upper airway musculature was examined by ultrasonography. All activity was quantified with subjects awake, during supine eupneic breathing while wearing a nasal mask connected to a pneumotachograph. Genioglossus EMG signals were analyzed offline by automated software (DQEMG), which extracted motor unit potential trains (MUPTs) contributed by individual motor units from the composite EMG signals. Quantitative measurements of MUP templates, including duration, peak-to-peak amplitude, area, area-to-amplitude ratio, and size index, were compared between the untreated patients with OSA and healthy control subjects. A total of 1,655 MUPTs from patients with OSA (n = 17; AHI, 55 ± 6/h) and control subjects (n = 14; AHI, 4 ± 1/h) were extracted from the genioglossus muscle EMG signals. MUP peak-to-peak amplitudes in the patients with OSA were not different compared with the control subjects (397.5 ± 9.0 vs. 382.5 ± 10.0 μV). However, the MUPs of the patients with OSA were longer in duration (11.5 ± 0.1 vs. 10.3 ± 0.1 ms; P < 0.001) and had a larger size index (4.09 ± 0.02 vs. 3.92 ± 0.02; P < 0.001) compared with control subjects. These results confirm and quantify the extent and existence of structural neural remodeling in OSA.

Surface EMG to assess and quantify upper airway dilators activity during non-invasive ventilation

This study tests the hypothesis that the surface electromyographic (EMG) activity of upper airway dilators would respond to inspiratory loading in a healthy humans model of ventilator trigger asynchrony. EMG activity was measured in levator alae-nasi, genioglossus, parasternal, scalene and diaphragm muscles in eight subjects. They breathed quietly through a face mask and then were connected to a mechanical ventilator. Recordings were performed during nasal breathing against negative pressure triggers (-2.5%, -5% and -10% of maximal inspiratory pressure) and during oro-nasal breathing with a "-10% trigger". Scalene, alae-nasi and genioglossus EMG activity level increased with the "-10% trigger". While no breathing route dependence was found in scalene, the significant increase was only found for nasal breathing in alae-nasi and for oro-nasal breathing in genioglossus. The dyspnea intensity was significantly correlated with the EMG activity level of these three muscles. Surface EMG of airway dilator muscles could be used as a complementary tool to assess inspiratory drive during mechanical ventilation.

Tonically Discharging Genioglossus Motor Units Show No Evidence of Rate Coding With Hypercapnia

The genioglossus (GG) is considered the principle protrudor muscle of the human tongue. Unlike most skeletal muscles, GG electromyographic (EMG) activities are robustly preserved in sleep and thus may fulfill a critical role in preserving airway patency. Previous studies in human subjects also confirm that the GG EMG increases in response to chemoreceptor and mechanoreceptor stimulation. This increase occurs secondary to the recruitment of previously inactive motor units (MUs) and/or an increase in firing rate of already active MUs. Which strategy the nervous system uses when the synaptic drive onto GG motoneurons increases is not known. Here we report on GG whole muscle and tonic MU activities under conditions that mimic sleep, i.e., mild-moderate elevations in CO(2) (3% inspired CO(2) or the addition of a 1.0 l dead space) and elevated airway resistance. Based on previous work in rat, we hypothesized that mild hypercapnia would increase the firing rates of tonic MUs and that these effects would be further potentiated by a modest increase in airway resistance. Fine wire and tungsten microelectrodes were inserted into the GG to record whole muscle and single MU activities in 21 subjects (13 women, 8 men; 20-55 yr). Either 3% inspired CO(2) or added dead space resulted in a 200-300% increase in the amplitude of both tonic and phasic components of the whole muscle GG EMG and a doubling of minute ventilation. Despite these changes, recordings obtained from a total of 84 tonically discharging GG single MUs provide no evidence of a change in firing rate under any of the conditions. On this basis we conclude that in healthy adults, the increase in the tonic component of the whole muscle GG EMG secondary to mild hypercapnia is due almost exclusively to the recruitment of previously inactive MUs.

The effect of mandibular advancement appliances on awake upper airway and masticatory muscle activity in patients with obstructive sleep apnoea

There is little understanding of how dental appliances, designed to posture the mandible forwards, act on pharyngeal airway dilatory and masticatory muscles in patients with obstructive sleep apnoea (OSA). This study evaluates, in a prospective cohort design, the effect of mandibular advancement splints (MAS) on awake genioglossus (GG), geniohyoid (GH) and masseter (M) muscle activity. Fifty OSA patients received a custom-made removable Herbst MAS appliance, adjusted for maximum therapeutic benefit, as judged by subjective improvement. Awake electromyographic (EMG) activity was recorded at baseline and with the MAS in situ, by using bipolar surface electrodes in patients seated upright and in the natural head position. The lower splint was modified to facilitate the placement of the intra-oral bipolar surface electrodes used to record GG EMG activity. Significant increases in GG (P = 0.041), GH (P<0.001) and M (P<0.001) muscle activity accompanied placement of the MAS. These findings support the contention of a physiological role, which may act to augment the anatomical action of MAS.

Heterogeneity in vertical positioning of the hyoid bone in relation to genioglossal activity in men.

The aim of this study was to investigate whether there is any relationship among genioglossus (GG) baseline electromyographic (EMG) activity, upper airway resistance, and sex. We hypothesized that GG baseline EMG activity and its response to pharyngeal partial occlusion may be heterogeneous in men but homogeneous in women. Lateral head roentgenograms were obtained in the upright standing position with the head at natural posture from age-matched, healthy, 16 men and 15 women. A miniature balloon was placed in the retroglossal pharynx, and a record of GG EMG response was measured. The database was divided by sex and further categorized based on the increment of GG EMG response to inflation of the balloon. Both sexes included responsive subjects showing a greater GG EMG activity increase than the mean values and a counterpart, ie, a nonresponsive group. When the two subgroups were compared, the hyoid bone of the responsive subjects positioned more inferiorly than that of nonresponsive subjects in men (P < .05). When men and women were compared, most cephalometric measurements were significantly larger in the male responders, but no difference was shown in the nonresponders. We concluded that men with a lower hyoid bone show greater GG reflexive response to the partial oropharyngeal obstruction.

Sex differences in genioglossus muscle response to changes in pharyngeal resistance

The genioglossus (GG) muscle's response to partial oropharyngeal occlusion was studied in age-matched, healthy awake men (n = 16) and women (n = 15). A miniature balloon was placed in the retroglossal pharynx, and the GG's electromyographic (EMG) reflexive response was evaluated in different body postures. We assumed that inflating the pharyngeal balloon and changing the body posture from upright to supine would increase pharyngeal airway resistance. Our hypothesis was that the change in airway resistance would elicit a different response in the GG muscle depending on sex. Our results showed that GG activity during natural breathing was higher in women than in men. GG EMG activity did not change upon inflation of the balloon in women. In contrast, when the balloon was inflated in the men, the GG's basal activity increased (P <.01) in both the upright and the supine positions. Women appeared to show a higher GG baseline EMG activity during spontaneous breathing at rest, while men were more responsive to the partial occlusion of the pharyngeal airway. (Am J Orthod Dentofacial Orthop 2002;122:500-5)

Mandibular Advancement Modulates Respiratory-Related Genioglossus Electromyographic Activity.

The purpose of this study was to determine if mandibular advancement had any effects on the respiratory-related electromyographic (EMG) activity of the genioglossus (GG) muscle in normal adults for both the upright and supine positions. Spontaneous GG EMG activity during quiet nasal breathing was recorded in 5 mandibular positions: centric occlusion (CO), maximal protrusion (MAX), 25% (MAX25), 50%(MAX50), and 75%(MAX75) of MAX. The maximal GG EMG activities during inspiration (GGinsp) and minimal GG EMG activities during expiration (GGexp) were compared. The GGinsp and GGexp significantly increased with mandibular advancement in both body positions. Furthermore, there were significant differences in both GGinsp and GGexp between CO and more protruded mandibular positions. However, no significant differences were found in the GGinsp at MAX compared to that at MAX75, and in the GGexp at MAX compared to those at MAX75 and MAX50. These results suggest that augmentation of the respiratory-related GG EMG activity with mandibular advancement diminishes the propensity of the upper airway to collapse. Moreover, the lack of any remarkable difference between the GGinsp at MAX75 and that at MAX may be relevant to the effectiveness of oral appliances in the treatment of obstructive sleep apnea.

Effect of intravenous substance P on laryngeal adductor activity in young dogs.

Reflex laryngeal adduction is a component of both the laryngeal chemoreflex and the esophagolaryngeal adductor reflex, two life-threatening reflexes that occur in immature animals. These two reflex responses are also thought to exist in infants and may play a role in causing life-threatening laryngospastic events and perhaps sudden infant death syndrome. Identifying neurotransmitters that mediate laryngeal adduction is important to understanding the mechanism of reflex laryngeal responses and to identifying potential means of pharmacologic prevention. Substance P (SP), a tachykinin, putatively functions as a sensory neurotransmitter and may play a role in mediating laryngeal reflexes. Substance P-immunoreactive-like fibers and receptors are present in the subepithelial tissues of the larynx, the vagus nerves, the nodose and jugular ganglia, and the vagal brain stem nuclei. In this investigation, the effect of SP infusion on laryngeal motor activity in an in vivo model is reported. Substance P was infused intravenously into 8 puppies (20 to 133 days of age, mean 81.2), on a mean of 3.0 occasions (range 1 to 6). Cardiovascular, respiratory, arterial blood gas, and cricothyroid (CT), thyroarytenoid (TA), and genioglossus electromyographic (EMG) responses to infusion of the tachykinin were recorded and subsequently analyzed. The SP infusion induced a marked increase in CT or TA EMG activity in 23 of 24 studies, and the increase was typically apparent within 60 seconds of the infusion. An increase in genioglossus EMG activity did not occur. An immediate, profound decrease in mean arterial pressure and an increase in respiratory rate and depth of chest wall excursion accompanied the laryngeal response. Arterial blood gas values remained unchanged (p > .05). The laryngeal adductor response to SP infusion was blocked when animals were pretreated with a systemic SP antagonist (Pfizer CP-96,345). This study demonstrates that peripheral infusion of the tachykinin SP induces a marked increase in laryngeal adductor activity. The response may be blocked by pretreatment of animals with a systemic SP antagonist. Because SP is thought to act primarily as a sensory neurotransmitter, these findings may be important in understanding the mechanism of reflex laryngeal adductor responses.

Breathing route dependence of upper airway muscle activity during hyperpnea.

Exercise (Ex) and hypercapnia (HC) both lead to increases in ventilation and upper airway muscle (UAM) activity. To determine whether different breathing routes (nasal vs. oral) or stimuli produced differential UAM activation, electromyographic (EMG) activity of the alae nasi (AN) and genioglossus (GG) were measured in seven normal subjects seated on a bicycle ergometer. Subjects performed paired runs during both progressive Ex and HC while breathing through the nose alone (N) or the mouth alone (O). During hyperpnea, AN EMG was greater when the subjects were breathing via N [81 +/- 6% maximum (HC) and 69 +/- 7% maximum (Ex)] than when they were breathing via O [30 +/- 5% maximum (HC) and 27 +/- 5% maximum (Ex); both P < 0.01], whereas the GG EMG did not differ between N and O. Both AN and GG EMG were similar for Ex and HC when the subjects were breathing via the same route. We conclude that UAM activation was independent of the nature of the stimulus. However, the AN muscle but not the GG muscle demonstrated breathing-route dependence of activity.

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.