Cranial muscle architecture in wild boar: Does captivity drive ontogenetic trajectories?

The jaw system in mammals is complex and different muscle morphotypes have been documented. Pigs are an interesting group of animals as they are omnivorous and have a bunodont crushing dentition. Moreover, they have interacted with humans for over 10,000 years and grow nearly two orders of magnitude in size. Despite being a model system for studies on cranial form and function, data on the growth of the jaw adductor muscles are scant. Moreover, whether captivity impacts the growth and architecture of the jaw adductors remains unknown. Based on dissection data of the jaw adductors of 45 animals ranging from less than 1 kg to almost 100 kg, we show that muscle masses, muscle fiber lengths, and cross-sectional areas scale as predicted for geometrically similar systems or with slight negative allometry. Only the fiber length of the lateral pterygoid muscle grew with slight positive allometry. Animals raised in captivity in stalls or in an enclosure were overall very similar to wild animals. However, some muscles were larger in captive animals. Interestingly, variation in bite force in captive animals was well predicted by the variation in the size of the superficial masseter muscle relative to the overall jaw adductor mass.

Gape drives regional variation in temporalis architectural dynamics in tufted capuchins.

Dynamic changes in jaw movements and bite forces depend on muscle architectural and neural factors that have rarely been compared within the same muscle. Here we investigate how regional muscle architecture dynamics-fascicle rotation, shortening, lengthening and architectural gear ratio (AGR)-vary during chewing across a functionally heterogeneous muscle. We evaluate whether timing in architecture dynamics relates to gape, food material properties and/or muscle activation. We also examine whether static estimates of temporalis fibre architecture track variation in dynamic architecture. Fascicle-level architecture dynamics were measured in three regions of the superficial temporalis of three adult tufted capuchins (Sapajus apella) using biplanar videoradiography and the XROMM workflow. Architecture dynamics data were paired with regional fine-wire electromyography data from four adult tufted capuchins. Gape accounted for most architectural change across the temporalis, but architectural dynamics varied between regions. Mechanically challenging foods were associated with lower AGRs in the anterior region. The timing of most dynamic architectural changes did not vary between regions and differed from regional variation in static architecture. Collectively these findings suggest that, when modelling temporalis muscle force production in extant and fossil primates, it is important to account for the effects of gape, regionalization and food material properties. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Characterizing tongue deformations during mastication using changes in planar components of three-dimensional angles.

Understanding of tongue deformations during mammalian mastication is limited, but has benefited from recent developments in multiplanar imaging technology. Here, we demonstrate how a standardized radiopaque marker implant configuration and biplanar fluoroscopy can quantify three-dimensional shape changes during chewing in pigs. Transverse and sagittal components of the three-dimensional angle between markers enable characterizing deformations in anatomically relevant directions. The transverse component illustrates bending to the left or to the right, which can occur symmetrically or asymmetrically, the latter sometimes indicating regional widening. The sagittal component reflects 'arching' or convex deformations in the dorsoventral dimension symmetrically or asymmetrically, the latter characteristic of twisting. Trends are detected in both the transverse and sagittal planes, and combinations thereof, to modify tongue shape in complex deformations. Both the transverse and sagittal components were also measured at key jaw and tongue positions, demonstrating variability particularly with respect to maximum and minimum gape. This highlights the fact that unlike tongue position, tongue deformations are more independent of jaw position, likely in response to the ever-changing bolus shape and position. From a methodological perspective, our study showcases advantages of a repeatable three-marker implant configuration suitable for animals of different sizes and highlights considerations for different implant patterns. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Oral processing, rheology, and mechanical response: Relations in a two-phase food model with anisotropic compounds.

Food-material poses a challenging matrix for objective material scientific description that matches the consumers' perception. With eyes on the emerging structured food materials from alternative protein sources, objectively describing perceived texture characteristics became a topic of interest to the food industry. This work made use of the well-known methodologies of jaw tracking and electromyography from the field of "food oral processing" and compared outcomes with mechanical responses to the deformation of model food systems to meat alternatives. To enable transferability to meat alternative products, an anisotropic structuring ingredient for alternative products, high-moisture texturized vegetable protein (HM-TVP), was embedded in an isotropic hydrocolloid gel. Data of the jaw movement and muscle activities exerted during mastication were modeled in a linear mixed model and set in relation to characteristic values obtained from small- and large-strain deformation. For improvement of the model fit, this work makes use of two new data-processing strategies in the field of oral processing: (i) Muscle activity data were set in relation to true forces and (ii) measured data were standardized and subjected to dimensional reduction. Based on that, model terms showed decreased p-values on various oral processing features. As a key outcome, it could be shown that an anisotropic structured phase induces more lateral jaw movement than isotropic samples, as was shown in meat model systems.

Ontogenetic changes in bite force and gape in tufted capuchins.

Bite force and gape are two important performance metrics of the feeding system, and these metrics are inversely related for a given muscle size because of fundamental constraints in sarcomere length-tension relationships. How these competing performance metrics change in developing primates is largely unknown. Here, we quantified in vivo bite forces and gapes across ontogeny and examined these data in relation to body mass and cranial measurements in captive tufted capuchins, Sapajus spp. Bite force and gape were also compared across geometric and mechanical properties of mechanically challenging foods to investigate relationships between bite force, gape and food accessibility (defined here as the ability to breach shelled nuts). Bite forces at a range of gapes and feeding behavioral data were collected from a cross-sectional ontogenetic series of 20 captive and semi-wild tufted capuchins at the Núcleo de Procriação de Macacos-Prego Research Center in Araçatuba, Brazil. These data were paired with body mass, photogrammetric measures of jaw length and facial width, and food geometric and material properties. Tufted capuchins with larger body masses had absolutely higher in vivo bite forces and gapes, and animals with wider faces had absolutely higher bite forces. Bite forces and gapes were significantly smaller in juveniles compared with subadults and adults. These are the first primate data to empirically demonstrate the gapes at which maximum active bite force is generated and to demonstrate relationships to food accessibility. These data advance our understanding of how primates meet the changing performance demands of the feeding system during development.

Modulation of reflex responses of the anterior and posterior bellies of the digastric muscle in freely moving rats.

BACKGROUND: Chewing and licking are primarily activated by central pattern generator (CPG) neuronal circuits in the brainstem and when activated trigger repetitive rhythmic orofacial movements such as chewing, licking and swallowing. These CPGs are reported to modulate orofacial reflex responses in functions such as chewing. OBJECTIVE: This study explored the modulation of reflex responses in the anterior and posterior bellies (ant-Dig and post-Dig, respectively) of the digastric muscle evoked by low-intensity trigeminal stimulation in conscious rats. METHODS: The ant-Dig and post-Dig reflexes were evoked by using low-intensity electrical stimulation applied to either the right or left inferior alveolar nerve. Peak-to-peak amplitudes and onset latencies were measured. RESULTS: No difference was observed between threshold and onset latency for evoking ant-Dig and post-Dig reflexes, suggesting that the latter was also evoked disynaptically. The peak-to-peak amplitude of both reflexes was significantly reduced during chewing, licking and swallowing as compared to resting period and was lowest during the jaw-closing phase of chewing and licking. Onset latency was significantly largest during the jaw-closing phase. Inhibitory level was similar between the ant-Dig and post-Dig reflex responses and between the ipsilateral and contralateral sides. CONCLUSION: These results suggest that both the ant-Dig and post-Dig reflex responses were significantly inhibited, probably due to CPG activation during feeding behaviours to maintain coordination of jaw and hyoid movements and hence ensure smooth feeding mechanics.

Sustained force production by the jaw-adductor muscles of a megalophagous frog, Ceratophrys cranwelli.

Most frogs have weak jaws that play a relatively minor role in tongue-mediated prey capture. Horned frogs (Ceratophrys spp.), however, follow the projection of a large tongue with a vice-like grip of their jaws to hold and immobilize prey. Prey include relatively large vertebrates, which they may restrain for minutes to possibly hours. High endurance behaviors, such as prolonged biting, require that muscles be capable of sustained force production. The feeding behavior of Ceratophrys suggests that their jaw-adductor muscles may be capable of powering sustained bites for long periods. We examined the capacity for sustained bite force by conducting an in situ experiment during which we measured bite force while bilaterally and supramaximally stimulating the jaw-adductor muscles of euthanized Cranwell's horned frogs (C. cranwelli). Muscles were stimulated for at least 60 min with a series of tetanic trains, with one experiment lasting over 6 h. We found that a significant sustained force develops during the first few minutes of the experiment, and this force is present between tetanic trains when the muscles are not being stimulated. The sustained force persists long after tetanic forces are barely detectable. The observed sustained force phenomenon parallels that observed for the jaw-adductor muscles of alligator lizards (Elgaria), another animal capable of sustained biting. The ability to bite with sustained and significant force by C. cranwelli may be facilitated by a configuration of different muscle fiber types, such as slow tonic fibers, as well as specializations in the muscle fibers that mitigate the effects of fatigue.

Effect of local administration of eicosapentaenoic acid on the jaw-opening reflex in rats.

Although eicosapentaenoic acid (EPA) application in vitro inhibits voltage-gated Na+ (Nav) channels in excitable tissues, the acute local effect of EPA on the jaw-opening reflex in vivo remains unknown. The aim of the present study was to determine whether local administration of EPA to adult male Wistar rats could attenuate the excitability of the jaw-opening reflex in vivo, including nociception. The jaw-opening reflex evoked by electrical stimulation of the tongue was recorded by a digastric muscle electromyogram (dEMG) in pentobarbital-anesthetized rats. The amplitude of the dEMG response was significantly increased in proportion to the electrical stimulation intensity (1×-5× threshold). At 3×, local administration of EPA dose-dependently inhibited the dEMG response, lasting 60 min, with maximum inhibition observed within approximately 10 min. The mean magnitude of dEMG signal inhibition by EPA was almost equal to that observed with a local anesthetic, 1% lidocaine, and with a half dose of lidocaine plus a half dose of EPA. These findings suggest that EPA attenuates the jaw-opening reflex, possibly by blocking Nav channels of primary nerve terminals, and strongly support the idea that EPA is a potential therapeutic agent and complementary alternative medicine for the prevention of acute trigeminal nociception.

A New Intraoral Six-Degrees-of-Freedom Jaw Movement Tracking Method Using Magnetic Fingerprints.

We proposed a novel jaw movement tracking method that can measure in six degrees of freedom. The magnetic field generated by a permanent magnet paired with a small, low-power-consumption Hall effect magnetic sensor is used to estimate the relative distance between two objects-in this instance, the lower and upper jaws. By installing a microelectromechanical system (MEMS) orientation sensor in the device, we developed a mouthpiece-type sensing device that can measure voluntary mandibular movements in three-dimensional orientation and position. An evaluation of individuals wearing this device demonstrated its ability to measure mandibular movement with an accuracy of approximately 3 mm. Using the movement recording feature with six degrees of freedom also enabled the evaluation of an individual's jaw movements over time in three dimensions. In this method, all sensors are built onto the mouthpiece and the sensing is completed in the oral cavity. It does not require the fixation of a large-scale device to the head or of a jig to the teeth, unlike existing mandibular movement tracking devices. These novel features are expected to increase the accessibility of routine measurements of natural jaw movement, unrestricted by an individual's physiological movement and posture.

Species-specific sensitivity to TGFß signaling and changes to the Mmp13 promoter underlie avian jaw development and evolution.

Precise developmental control of jaw length is critical for survival, but underlying molecular mechanisms remain poorly understood. The jaw skeleton arises from neural crest mesenchyme (NCM), and we previously demonstrated that these progenitor cells express more bone-resorbing enzymes including Matrix metalloproteinase 13 (Mmp13) when they generate shorter jaws in quail embryos versus longer jaws in duck. Moreover, if we inhibit bone resorption or Mmp13, we can increase jaw length. In the current study, we uncover mechanisms establishing species-specific levels of Mmp13 and bone resorption. Quail show greater activation of and sensitivity to transforming growth factor beta (TGFß) signaling than duck; where intracellular mediators like SMADs and targets like Runt-related transcription factor 2 (Runx2), which bind Mmp13, become elevated. Inhibiting TGFß signaling decreases bone resorption, and overexpressing Mmp13 in NCM shortens the duck lower jaw. To elucidate the basis for this differential regulation, we examine the Mmp13 promoter. We discover a SMAD-binding element and single nucleotide polymorphisms (SNPs) near a RUNX2-binding element that distinguish quail from duck. Altering the SMAD site and switching the SNPs abolish TGFß sensitivity in the quail Mmp13 promoter but make the duck promoter responsive. Thus, differential regulation of TGFß signaling and Mmp13 promoter structure underlie avian jaw development and evolution.

Loss of oral sensation impairs feeding performance and consistency of tongue-jaw coordination.

BACKGROUND: Individuals with impaired oral sensation report difficulty chewing, but little is known about the underlying changes to tongue and jaw kinematics. Methodological challenges impede the measurement of 3D tongue movement and its relationship to the gape cycle. OBJECTIVE: The aim of this study was to quantify the impact of loss of oral somatosensation on feeding performance, 3D tongue kinematics and tongue-jaw coordination. METHODOLOGY: XROMM (X-ray Reconstruction of Moving Morphology) was used to quantify 3D tongue and jaw kinematics during feeding in three rhesus macaques (Macaca mulatta) before and after an oral tactile nerve block. Feeding performance was measured using feeding sequence duration, number of manipulation cycles and swallow frequency. Coordination was measured using event- and correlation-based metrics of jaw pitch, anterior tongue length, width and roll. RESULTS: In the absence of tactile sensation to the tongue and other oral structures, feeding performance decreased, and the fast open phase of the gape cycle became significantly longer, relative to the other phases (p < .05). The tongue made similar shapes in both the control and nerve block conditions, but the pattern of tongue-jaw coordination became significantly more variable after the block (p < .05). CONCLUSION: Disruption of oral somatosensation impacts feeding performance by introducing variability into the typically tight pattern of tongue-jaw coordination.

Thyroid hormone shapes craniofacial bones during postembryonic zebrafish development.

Changing the shape of craniofacial bones can profoundly alter ecological function, and understanding how developmental conditions sculpt skeletal phenotypes can provide insight into evolutionary adaptations. Thyroid hormone (TH) stimulates metamorphosis and regulates skeletal morphogenesis across vertebrates. To assess the roles of this hormone in sculpting the craniofacial skeleton of a non-metamorphic vertebrate, we tested zebrafish for developmental periods of TH-induced craniofacial shape change. We analyzed shapes of specific bones that function in prey detection, capture and processing. We quantified these elements from late-larval through adult stages under three developmental TH profiles. Under wild-type conditions, each bone progressively grows allometrically into a mature morphology over the course of postembryonic development. In three of the four bones, TH was required to sculpt an adult shape: hypothyroidism inhibited aspects of shape change, and allowed some components of immature shape to be retained into adulthood. Excess developmental TH stimulated aspects of precocious shape change leading to abnormal morphologies in some bones. Skeletal features with functional importance showed high sensitivities to TH, including the transformator process of the tripus, the mandibular symphysis of the lower jaw, the scutiform lamina of the hyomandibula, and the anterior arm of the pharyngeal jaw. In all, we found that TH is necessary for shaping mature morphology of several essential skeletal elements; this requirement is particularly pronounced during larval development. Altered TH titer leads to abnormal morphologies with likely functional consequences, highlighting the potential of TH and downstream pathways as targets for evolutionary change.

Methodology for eliciting the brainstem trigeminal-hypoglossal reflex in humans under general anesthesia.

OBJECTIVE: Brainstem trigeminal-hypoglossal reflexes (THRs), also known as the jaw-tongue reflexes, coordinate the position of the tongue in the mouth in relation to the jaw movement during oromotor behaviors such as mastication, swallowing, vocalization, and breathing. Their use in brainstem surgery however, has never been assessed in spite of its potential benefit possibly due to the lack of a methodology to elicit these reflexes under general anesthesia. METHODS: We proposed a technique to elicit the THRs during total intravenous anesthesia (TIVA) consisting on a V3 infrazygomatic train stimulation paradigm and recording from the Styloglossus (31 patients) and the Genioglossus (21 patients) muscles to elicit long latency responses. RESULTS: The THR was successfully recorded using the V3 stimulation point in 82.1% of patients, of which 96.9% presented a response on the Styloglossus muscle (Jaw-opening reflex) while 0.06% presented a response on the Genioglossus muscle instead (Jaw-closing reflex). CONCLUSIONS: The THRs can be successfully recorded in surgery under general anaesthesia with the predominant reflex seen being the jaw-opening reflex. SIGNIFICANCE: We provide a novel method to elicit the THRs during general anesthesia, which could be of aid in brainstem surgery.

A novel intramandibular joint facilitates feeding versatility in the sixbar distichodus.

The intramandibular joint (IMJ) is a secondary point of movement between the two major bones of the lower jaw. It has independently evolved in several groups of teleost fishes, each time representing a departure from related species in which the mandible functions as a single structure rotating only at the quadratomandibular joint (QMJ). In this study, we examine kinematic consequences of the IMJ novelty in a freshwater characiform fish, the herbivorous Distichodus sexfasciatus. We combine traditional kinematic approaches with trajectory-based analysis of motion shapes to compare patterns of prey capture movements during substrate biting, the fish's native feeding mode, and suction of prey from the water column. We find that the IMJ enables complex jaw motions and contributes to feeding versatility by allowing the fish to modulate its kinematics in response to different prey and to various scenarios of jaw-substrate interaction. Implications of the IMJ include context-dependent movements of lower versus upper jaws, enhanced lower jaw protrusion, and the ability to maintain contact between the teeth and substrate throughout the jaw closing or biting phase of the motion. The IMJ in D. sexfasciatus appears to be an adaptation for removing attached benthic prey, consistent with its function in other groups that have evolved the joint. This study builds on our understanding of the role of the IMJ during prey capture and provides insights into broader implications of the innovative trait.

Relationships between dietary breadth and flexibility in jaw movement: A case study of two recently diverged insular populations of Podarcis lizards.

The kinematics of lizard feeding are the result of complex interactions between the craniocervical, the hyolingual, and the locomotor systems. The coordinated movement of these elements is driven by sensory feedback from the tongue and jaws during intraoral transport. The kinematics of jaw movements have been suggested to be correlated with the functional characteristics of the prey consumed, such as prey mobility and hardness. However, whether and how dietary breadth correlates with the flexibility in the behavioral response has rarely been tested, especially at the intraspecific level. Here we tested whether an increase in dietary breadth was associated with a greater behavioral flexibility by comparing two recently diverged populations of insular Podarcis lizards differing in dietary breadth. To do so, we used a stereoscopic high-speed camera set-up to analyze the jaw kinematics while offering them different prey types. Our results show that prey type impacts kinematics, especially maximum gape, and maximum opening and closing speed. Furthermore, the behavioral flexibility was greater in the population with the greater dietary breadth, suggesting that populations which naturally encounter and feed on more diverse prey items show a greater ability to modulate their movements to deal with variation in functionally relevant prey properties. Finally, the more generalist population showed more stereotyped movements suggesting a finer motor control.

Suction feeding biomechanics of Polypterus bichir: investigating linkage mechanisms and the contributions of cranial kinesis to oral cavity volume change.

Many fishes use substantial cranial kinesis to rapidly increase buccal cavity volume, pulling prey into the mouth via suction feeding. Living polypterids are a key lineage for understanding the evolution and biomechanics of suction feeding because of their phylogenetic position and unique morphology. Polypterus bichir have fewer mobile cranial elements compared with teleosts [e.g. immobile (pre)maxillae] but successfully generate suction through dorsal, ventral and lateral oral cavity expansion. However, the relative contributions of these motions to suction feeding success have not been quantified. Additionally, extensive body musculature and lack of opercular jaw opening linkages make P. bichir of interest for examining the role of cranial versus axial muscles in driving mandibular depression. Here, we analyzed the kinematics of buccal expansion during suction feeding in P. bichir using X-ray Reconstruction of Moving Morphology (XROMM) and quantified the contributions of skeletal elements to oral cavity volume expansion and prey capture. Mouth gape peaks early in the strike, followed by maximum cleithral and ceratohyal rotations, and finally by opercular and suspensorial abductions, maintaining the anterior-to-posterior movement of water. Using a new method of quantifying bones' relative contributions to volume change (RCVC), we demonstrate that ceratohyal kinematics are the most significant drivers of oral cavity volume change. All measured cranial bone motions, except abduction of the suspensorium, are correlated with prey motion. Lastly, cleithral retraction is largely concurrent with ceratohyal retraction and jaw depression, while the sternohyoideus maintains constant length, suggesting a central role of the axial muscles, cleithrum and ceratohyal in ventral expansion.

The relationship between head shape, head musculature and bite force in caecilians (Amphibia: Gymnophiona).

Caecilians are enigmatic limbless amphibians that, with a few exceptions, all have an at least partly burrowing lifestyle. Although it has been suggested that caecilian evolution resulted in sturdy and compact skulls as an adaptation to their head-first burrowing habits, no relationship between skull shape and burrowing performance has been demonstrated to date. However, the unique dual jaw-closing mechanism and the osteological variability of their temporal region suggest a potential relationship between skull shape and feeding mechanics. Here, we explored the relationships between skull shape, head musculature and in vivo bite forces. Although there is a correlation between bite force and external head shape, no relationship between bite force and skull shape could be detected. Whereas our data suggest that muscles are the principal drivers of variation in bite force, the shape of the skull is constrained by factors other than demands for bite force generation. However, a strong covariation between the cranium and mandible exists. Moreover, both cranium and mandible shape covary with jaw muscle architecture. Caecilians show a gradient between species with a long retroarticular process associated with a large and pennate-fibered m. interhyoideus posterior and species with a short process but long and parallel-fibered jaw adductors. Our results demonstrate the complexity of the relationship between form and function of this jaw system. Further studies that focus on factors such as gape distance or jaw velocity will be needed in order to fully understand the evolution of feeding mechanics in caecilians.

Functional and ecological correlates of the primate jaw abductors.

While the adductor musculature of the primate jaw has been extensively analyzed within the context of dietary and social ecology, little is known about the corresponding muscles of jaw abduction. Nonetheless, these muscles significantly contribute to a species' maximum gape potential, and thus might constrain dietary niche diversity and impact social display behaviors. In this study, we quantify the architectural properties of the digastric (a jaw abductor) and lateral pterygoid (a jaw abductor and anterior translator) across a broad sample of male and female anthropoid primates. We test the hypothesis that the abductor musculature reflects specialization to dietary and behavioral ecology. Our sample comprises 14 catarrhine and 13 platyrrhine species spanning a wide range of dietary and social categories. All specimens were sharp dissected and muscles subsequently chemically digested using a standardized protocol. Our findings demonstrate that relative fascicle lengths within the lateral pterygoid (but not the digastric) are significantly greater within species that habitually consume larger food items. Meanwhile, canine length is more strongly associated with fascicle lengths in the digastric than in the lateral pterygoid, particularly within males. Neither dietary mechanical resistance nor the intensity of social competition relates to the size or architectural properties of the jaw abductors. These findings suggest that dietary-and to a lesser extent, socioecological-aspects of a primate's life history may be reflected in the architecture of these muscles, albeit to varying degrees. This underlines the importance of considering the complete masticatory apparatus when interpreting the evolution of the primate jaw.

Home-Based Monitoring of Eating in Adolescents: A Pilot Study.

OBJECTIVES: To investigate eating episodes in a group of adolescents in their home-setting using wearable electromyography (EMG) and camera, and to evaluate the agreement between the two devices. APPROACH: Fifteen adolescents (15.5 ± 1.3 years) had a smartphone-assisted wearable-EMG device attached to the jaw to assess chewing features over one evening. EMG outcomes included chewing pace, time, episode count, and mean power. An automated wearable-camera worn on the chest facing outwards recorded four images/minute. The agreement between the camera and the EMG device in detecting eating episodes was evaluated by calculating specificity, sensitivity, and accuracy. MAIN RESULTS: The features of eating episodes identified by EMG throughout the entire recording time were (mean (SD)); chewing pace 1.64 (0.20) Hz, time 10.5 (10.4) minutes, episodes count 56.8 (39.0), and power 32.1% (4.3). The EMG device identified 5.1 (1.8) eating episodes lasting 27:51 (16:14) minutes whereas the cameras indicated 2.4 (2.1) episodes totaling 14:49 (11:18) minutes, showing that the EMG-identified chewing episodes were not all detected by the camera. However, overall accuracy of eating episodes identified ranged from 0.8 to 0.92. SIGNIFICANCE: The combination of wearable EMG and camera is a promising tool to investigate eating behaviors in research and clinical-settings.

A medullary centre for lapping in mice.

It has long been known that orofacial movements for feeding can be triggered, coordinated, and often rhythmically organized at the level of the brainstem, without input from higher centers. We uncover two nuclei that can organize the movements for ingesting fluids in mice. These neuronal groups, IRtPhox2b and Peri5Atoh1, are marked by expression of the pan-autonomic homeobox gene Phox2b and are located, respectively, in the intermediate reticular formation of the medulla and around the motor nucleus of the trigeminal nerve. They are premotor to all jaw-opening and tongue muscles. Stimulation of either, in awake animals, opens the jaw, while IRtPhox2b alone also protracts the tongue. Moreover, stationary stimulation of IRtPhox2b entrains a rhythmic alternation of tongue protraction and retraction, synchronized with jaw opening and closing, that mimics lapping. Finally, fiber photometric recordings show that IRtPhox2b is active during volitional lapping. Our study identifies one of the subcortical nuclei underpinning a stereotyped feeding behavior.