Gape Cycle Research Articles

Prolonged use of a soft diet during early growth and development alters feeding behavior and chewing kinematics in a young animal model.

In infants and children with feeding and swallowing issues, modifying solid foods to form a liquid or puree is used to ensure adequate growth and nutrition. However, the behavioral and neurophysiological effects of prolonged use of this intervention during critical periods of postnatal oral skill development have not been systematically examined, although substantial anecdotal evidence suggests that it negatively impacts downstream feeding motor and coordination skills, possibly due to immature sensorimotor development. Using an established animal model for infant and juvenile feeding physiology, we leverage X-ray reconstruction of moving morphology to compare feeding behavior and kinematics between 12-week-old pigs reared on solid chow (control) and an age- and sex-matched cohort raised on the same chow softened to a liquid. When feeding on two novel foods, almond and apple, maintenance on a soft diet decreases gape cycle duration, resulting in a higher chewing frequency. When feeding on almonds, pigs in this group spent less time ingesting foods compared to controls, and chewing cycles were characterized by less jaw rotation about a dorsoventral axis (yaw) necessary for food reduction. There was also a reduced tendency to alternate chewing side with every chew during almond chewing, a behavioral pattern typical of pigs. These more pronounced impacts on behavior and kinematics during feeding on almonds, a tougher and stiffer food than apples, suggest that food properties mediate the behavioral and physiological impacts of early texture modificationand that the ability to adapt to different food properties may be underdeveloped. In contrast, the limited effects of food texture modification on apple chewing indicate that such intervention/treatment does not alter feeding behavior of less challenging foods. Observed differences cannot be attributed to morphology because texture modification over the treatment period had limited impact on craniodental growth. Short-term impacts of soft-texture modification during postweaning development on feeding dynamics should be considered as potential negative outcomes of this treatment strategy.

Dynamic finite element modelling of the macaque mandible during a complete mastication gape cycle.

Three-dimensional finite element models (FEMs) are powerful tools for studying the mechanical behaviour of the feeding system. Using validated, static FEMs we have previously shown that in rhesus macaques the largest food-related differences in strain magnitudes during unilateral postcanine chewing extend from the lingual symphysis to the endocondylar ridge of the balancing-side ramus. However, static FEMs only model a single time point during the gape cycle and probably do not fully capture the mechanical behaviour of the jaw during mastication. Bone strain patterns and moments applied to the mandible are known to vary during the gape cycle owing to variation in the activation peaks of the jaw-elevator muscles, suggesting that dynamic models are superior to static ones in studying feeding biomechanics. To test this hypothesis, we built dynamic FEMs of a complete gape cycle using muscle force data from in vivo experiments to elucidate the impact of relative timing of muscle force on mandible biomechanics. Results show that loading and strain regimes vary across the chewing cycle in subtly different ways for different foods, something which was not apparent in static FEMs. These results indicate that dynamic three-dimensional FEMs are more informative than static three-dimensional FEMs in capturing the mechanical behaviour of the jaw during feeding by reflecting the asymmetry in jaw-adductor muscle activations during a gape cycle. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Rhythmic chew cycles with distinct fast and slow phases are ancestral to gnathostomes.

Intra-oral food processing, including chewing, is important for safe swallowing and efficient nutrient assimilation across tetrapods. Gape cycles in tetrapod chewing consist of four phases (fast open and -close, and slow open and -close), with processing mainly occurring during slow close. Basal aquatic-feeding vertebrates also process food intraorally, but whether their chew cycles are partitioned into distinct phases, and how rhythmic their chewing is, remains unknown. Here, we show that chew cycles from sharks to salamanders are as rhythmic as those of mammals, and consist of at least three, and often four phases, with phase distinction occasionally lacking during jaw opening. In fishes and aquatic-feeding salamanders, fast open has the most variable duration, more closely resembling mammals than basal amniotes (lepidosaurs). Across ontogenetically or behaviourally mediated terrestrialization, salamanders show a distinct pattern of the second closing phase (near-contact) being faster than the first, with no clear pattern in partitioning of variability across phases. Our results suggest that distinct fast and slow chew cycle phases are ancestral for jawed vertebrates, followed by a complicated evolutionary history of cycle phase durations and jaw velocities across fishes, basal tetrapods and mammals. These results raise new questions about the mechanical and sensorimotor underpinnings of vertebrate food processing. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Three-dimensional mandibular kinematics of mastication in the marsupial Didelphis virginiana.

Didelphis virginiana (the Virginia opossum) is often used as an extant model for understanding feeding behaviour in Mesozoic mammaliaforms, primarily due to their morphological similarities, including an unfused mandibular symphysis and tribosphenic molars. However, the three-dimensional jaw kinematics of opossum chewing have not yet been fully quantified. We used biplanar videofluoroscopy and the X-Ray Reconstruction of Moving Morphology workflow to quantify mandibular kinematics in four wild-caught opossums feeding on hard (almonds) and soft (cheese cubes) foods. These data were used to test hypotheses regarding the importance of roll versus yaw in chewing by early mammals, and the impact of food material properties (FMPs) on jaw kinematics. The magnitude of roll exceeds that of yaw, but both are necessary for tooth-tooth or tooth-food-tooth contact between complex occlusal surfaces. We confirmed the utility of the four vertical kinematic gape cycle phases identified in tetrapods but we further defined two more in order to capture non-vertical kinematics. Statistical tests support the separation of chew cycle phases into two functional groups: occlusal and non-occlusal phases. The separation of slow close into two (occlusal) phases gives quantitative kinematic support for the long-hypothesized multifunctionality of the tribosphenic molar. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

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

BackgroundIndividuals 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.ObjectiveThe aim of this study was to quantify the impact of loss of oral somatosensation on feeding performance, 3D tongue kinematics and tongue‐jaw coordination.MethodologyXROMM (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.ResultsIn 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).ConclusionDisruption of oral somatosensation impacts feeding performance by introducing variability into the typically tight pattern of tongue‐jaw coordination.

3D Hyolingual Kinematics Reveal New Insights Into the Biomechanical and Neural Control of Chewing and Swallowing in Macaque Primates

Hyolingual kinematics are difficult to measure, but are central to hypotheses regarding musculoskeletal mechanisms and motor control. Recent application of biplanar videoradiography to the study of hyolingual kinematics in nonhuman primates provides new insight into tongue movements during chewing and swallowing, and into the role of hyoid movement in tongue base retraction and the oral phase of swallowing. During grape chewing, complex shape changes in the tongue were dominated by a combination of flexion in the tongue’s sagittal planes and roll about its long axis. As hypothesized for humans, in macaques during tongue retraction the molar region of the tongue rolls to the chewing side simultaneous with sagittal flexion, while the tongue tip flexes to the balancing side. Twisting and flexion reach their maxima early in the fast close phase of chewing cycles, positioning the food bolus between the approaching teeth prior to the power stroke. The muscular drivers of these movements are likely to include a combination of intrinsic and extrinsic tongue muscles. Nerve block of tactile sensation from trigeminal innervated oral structures decreased feeding performance, and the fast open phase of the gape cycle became significantly longer, relative to the other phases. 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. Disruption of oral somatosensation impacts feeding performance by introducing variability into the typically tight pattern of tongue‐jaw coordination. During primate swallowing, tongue base retraction (TBR) drives the food bolus across the oropharynx towards the esophagus but the mechanics of TBR are poorly understood. XROMM of four macaque monkeys falsifies both the hypothesis that extrinsic tongue muscle shortening pulls the tongue base posteriorly, and the muscular hydrostat hypothesis that intrinsic muscle shortening displaces the tongue base posteriorly by increasing tongue length. Our data suggest a novel hydraulic mechanism of TBR: shortening and rotation of suprahyoid muscles compresses the tongue between the hard palate, hyoid and mouth floor, squeezing the midline tongue base and food bolus back into the oropharynx. Hyoid elevation and protraction are powered by concentric activation and rotation of mylohyoid and digastric, followed by concentric activation of geniohyoid. This research suggests that structure, function, and coordination of mylohyoid and geniohyoid muscles are especially important determinants of swallowing performance in macaques, and probably humans.

Prey capture kinematics of wild and hatchery juvenile common snook Centropomus undecimalis

Common snook Centropomus undecimalis is an important estuarine-dependent predatory fish species. In Florida, the decline of wild stocks, due mainly to fishing pressure and loss of habitat, has led to increasingly restrictive management actions in the last 50 years. This has also promoted its culture for stock enhancement as one of many management actions. Stocking efforts indicate that survival of snook fingerlings can be poor and improvements could be achieved through prerelease conditioning. In this study we compared prey capture kinematics between naïve hatchery juvenile snook and wild conspecifics. Capture behavior, quantified with high-speed cameras, identified specific differences in prey capture of hatchery and wild snook. Naïve juvenile hatchery snook exposed to live prey made fewer attempts to feed, had longer delays in the time to strike, exhibited higher strike velocities and engulfed prey earlier in the gape cycle, and had less overall feeding success compared to wild fish. However, experience with repeated live prey feeding events quickly improved hatchery snook feeding success, similar to wild fish. Therefore, prerelease training via exposure to live prey could improve feeding performance and overall fate of snook released into the wild.

Regional Tongue Deformations During Chewing and Drinking in the Pig.

SynopsisAs a muscular hydrostat, the tongue undergoes complex deformations during most oral behaviors, including chewing and drinking. During thesebehaviors, deformations occur in concert with tongue and jaw movements to position and transport the bolus. Moreover, the various parts of the tongue may move and deform at similar timepoints relative to the gape cycle or they may occur at different timepoints, indicating regional biomechanical and functional variation. The goal of this study is to quantify tongue deformations during chewing and drinking in pigs by characterizing intrinsic changes in tongue dimensions (i.e., length and width) across multiple regions simultaneously. Tongue deformations are generally larger during chewing cycles compared to drinking cycles. Chewing and drinking also differ in the timing, relative to the gape cycle, of regional length and width, but not total length, deformations. This demonstrates functional differences in the temporal dynamics of localized shape changes, whereas the global properties of jaw–tongue coordination are maintained. Finally, differences in the trade-off between length and width deformations demonstrate that the properties of a muscular hydrostat are observed at the whole tongue level, but biomechanical variation (e.g., changes in movements and deformations) at the regional level exists. This study provides new critical insights into the regional contributions to tongue deformations as a basis for future work on multidimensional shape changes in soft tissues.

Jaw kinematics and tongue protraction-retraction during chewing and drinking in the pig.

Mastication and drinking are rhythmic and cyclic oral behaviors that require interactions between the tongue, jaw and a food or liquid bolus, respectively. During mastication, the tongue transports and positions the bolus for breakdown between the teeth. During drinking, the tongue aids in ingestion and then transports the bolus to the oropharynx. The objective of this study was to compare jaw and tongue kinematics during chewing and drinking in pigs. We hypothesized there would be differences in jaw gape cycle dynamics and tongue protraction-retraction between behaviors. Mastication cycles had an extended slow-close phase, reflecting tooth-food-tooth contact, whereas drinking cycles had an extended slow-open phase, corresponding to tongue protrusion into the liquid. Compared with chewing, drinking jaw movements were of lower magnitude for all degrees of freedom examined (jaw protraction, yaw and pitch), and were bilaterally symmetrical with virtually no yaw. The magnitude of tongue protraction-retraction (Txt), relative to a mandibular coordinate system, was greater during mastication than during drinking, but there were minimal differences in the timing of maximum and minimum Txt relative to the jaw gape cycle between behaviors. However, during drinking, the tongue tip is often located outside the oral cavity for the entire cycle, leading to differences between behaviors in the timing of anterior marker maximum Txt. This demonstrates that there is variation in tongue-jaw coordination between behaviors. These results show that jaw and tongue movements vary significantly between mastication and drinking, which hints at differences in the central control of these behaviors.

Elastic recoil action amplifies jaw closing speed in an aquatic feeding salamander.

Tendon springs often influence locomotion by amplifying the speed and power of limb joint rotation. However, less is known about elastic recoil action in feeding systems, particularly for small aquatic animals. Here, we ask if elastic recoil amplifies the speed of gape closing during aquatic food processing in the Axolotl (Ambystoma mexicanum). We measure activation of the adductor mandibulae externus via electromyography and strain of the jaw adductor muscle-tendon unit (MTU), and gape kinematics via fluoromicrometry. The muscle is pre-activated coincident with gape opening, which causes MTU stretch. Activation lasts significantly shorter for fish than cricket processing, and muscle shortening during MTU lengthening yields significantly greater elastic strain for cricket processing. The speed of MTU shortening, which dictates the speed of gape closing is 2.5-4.4 times greater than the speed of the initial shortening of the muscle fascicles for fish and cricket gape cycles, respectively. These data demonstrate a clear role for elastic recoil, which may be unexpected for a MTU in a feeding system of a small, aquatic animal. Amplification of jaw-closing speed resulting from elastic recoil likely confers ecological advantages in reducing prey escape risks during food processing in a dense and viscous fluid environment.

Muscle architecture dynamics modulate performance of the superficial anterior temporalis muscle during chewing in capuchins

Jaw-muscle architecture is a key determinant of jaw movements and bite force. While static length-force and force-velocity relationships are well documented in mammals, architecture dynamics of the chewing muscles and their impact on muscle performance are largely unknown. We provide novel data on how fiber architecture of the superficial anterior temporalis (SAT) varies dynamically during naturalistic feeding in tufted capuchins (Sapajus apella). We collected data on architecture dynamics (changes in muscle shape or the architectural gear ratio) during the gape cycle while subjects fed on foods of different mechanical properties. Architecture of the SAT varied with phases of the gape cycle, but gape distance accounted for the majority of dynamic changes in architecture. In addition, lower gear ratios (low muscle velocity relative to fascicle velocity) were observed when animals chewed on more mechanically resistant foods. At lower gear ratios, fibers rotated less during shortening resulting in smaller pinnation angles, a configuration that favors increased force production. Our results suggest that architectural dynamics may influence jaw-muscle performance by enabling the production of higher bite forces during the occlusal phase of the gape cycle and while processing mechanically challenging foods.

Unilateral lingual nerve transection alters jaw-tongue coordination during mastication in pigs.

During chewing, movements and deformations of the tongue are coordinated with jaw movements to manage and manipulate the bolus and avoid injury. Individuals with injuries to the lingual nerve report both tongue injuries due to biting and difficulties in chewing, primarily because of impaired bolus management, suggesting that jaw-tongue coordination relies on intact lingual afferents. Here, we investigate how unilateral lingual nerve (LN) transection affects jaw-tongue coordination in an animal model (pig, Sus scrofa). Temporal coordination between jaw pitch (opening-closing) and 1) anteroposterior tongue position (i.e., protraction-retraction), 2) anteroposterior tongue length, and 3) mediolateral tongue width was compared between pre- and post-LN transection using cross-correlation analyses. Overall, following LN transection, the lag between jaw pitch and the majority of tongue kinematics decreased significantly, demonstrating that sensory loss from the tongue alters jaw-tongue coordination. In addition, decrease in jaw-tongue lag suggests that, following LN transection, tongue movements and deformations occur earlier in the gape cycle than when the lingual sensory afferents are intact. If the velocity of tongue movements and deformations remains constant, earlier occurrence can reflect less pronounced movements, possibly to avoid injuries. The results of this study demonstrate that lingual afferents participate in chewing by assisting with coordinating the timing of jaw and tongue movements. The observed changes may affect bolus management performance and/or may represent protective strategies because of altered somatosensory awareness of the tongue.NEW & NOTEWORTHY Chewing requires coordination between tongue and jaw movements. We compared the coordination of tongue movements and deformation relative to jaw opening-closing movements pre- and post-lingual nerve transection during chewing in pigs. These experiments reveal that the timing of jaw-tongue coordination is altered following unilateral disruption of sensory information from the tongue. Therefore, maintenance of jaw-tongue coordination requires bilateral sensory information from the tongue.

Effects of food properties on chewing in pigs: Flexibility and stereotypy of jaw movements in a mammalian omnivore

Chewing is a rhythmic oral behavior that requires constant modifications of jaw movements in response to changes in food properties. The food-specific kinematic response is dependent on the potential for kinematic flexibility allowed by morphology and modulation of motor control. This study investigates the effects of food toughness and stiffness on the amplitude and variability of jaw movements during chewing in a typical omnivorous mammalian model (pigs). Jaw movements were reconstructed using X-ray Reconstruction Of Moving Morphology (XROMM) and kinematic data associated with the amplitude of jaw pitch (opening-closing) and jaw yaw (mediolateral rotation) were extracted for each cycle. Between-food differences were tested for the amplitude of jaw movements during each phase of the gape cycle, as well as in their respective within-food variability, or stereotypy, as indicated by coefficients of variation. With increasing toughness, jaw pitch amplitude is decreased during fast close, larger and more stereotyped during slow close, smaller but more variable during slow open, and more variable during fast open. In addition, when chewing on tougher foods, the amplitude of jaw yaw during slow close only increases in a subset of individuals, but all become less variable (i.e., more stereotyped). In contrast, increasing food stiffness has no effect on the amplitude or the variability of jaw pitch, whereas jaw yaw increases significantly in the majority of individuals studied. Our data demonstrate that food stiffness and toughness both play a role in modulating gape cycle dynamics by altering the trajectory of jaw movements, especially during the slow-close phase and tooth-food-tooth contact, albeit differently. This highlights how a generalist oral morphology such as that of pigs (e.g., bunodont teeth lacking precise occlusion, permissive temporomandibular joint allowing extensive condylar displacements in 3 dimensions) enables organisms to not only adjust chewing movements in their amplitude, but also in their variability.

Jaw kinematics and mandibular morphology in humans

Understanding the influence of feeding behavior on mandibular morphology is necessary for interpreting dietary change in fossil hominins. However, mandibular morphology is also likely to have an effect on feeding behavior, including jaw kinematics. Here we examine the relationships between mandibular morphology and jaw kinematics in humans using landmark-based morphometrics to quantify jaw movement. Three-dimensional movements of reflective markers coupled to the mandible and cranium were used to capture jaw movements while subjects chewed cubes of raw and cooked sweet potato. Geometric morphometric methods were adapted to quantify and analyze gape cycle motion paths. Gape cycles varied significantly across chewing sequences and between raw and cooked sweet potato. Variation in gape cycle size and shape is related to the width (intergonial distance) and length of the mandible. These results underline the fact that jaw kinematic variation within and between taxa is related to and may be influenced by mandibular morphology. Future studies examining kinematic variation should assess the influence of morphological differences on movement.

Dynamics of motor cortical activity during naturalistic feeding behavior

Objective. The orofacial primary motor cortex (MIo) plays a critical role in controlling tongue and jaw movements during oral motor functions, such as chewing, swallowing and speech. However, the neural mechanisms of MIo during naturalistic feeding are still poorly understood. There is a strong need for a systematic study of motor cortical dynamics during feeding behavior. Approach. To investigate the neural dynamics and variability of MIo neuronal activity during naturalistic feeding, we used chronically implanted micro-electrode arrays to simultaneously recorded ensembles of neuronal activity in the MIo of two monkeys (Macaca mulatta) while eating various types of food. We developed a Bayesian nonparametric latent variable model to reveal latent structures of neuronal population activity of the MIo and identify the complex mapping between MIo ensemble spike activity and high-dimensional kinematics. Main results. Rhythmic neuronal firing patterns and oscillatory dynamics are evident in single-unit activity. At the population level, we uncovered the neural dynamics of rhythmic chewing, and quantified the neural variability at multiple timescales (complete feeding sequences, chewing sequence stages, chewing gape cycle phases) across food types. Our approach accommodates time-warping of chewing sequences and automatic model selection, and maps the latent states to chewing behaviors at fine timescales. Significance. Our work shows that neural representations of MIo ensembles display spatiotemporal patterns in chewing gape cycles at different chew sequence stages, and these patterns vary in a stage-dependent manner. Unsupervised learning and decoding analysis may reveal the link between complex MIo spatiotemporal patterns and chewing kinematics.

The effect of unilateral lingual nerve injury on the kinematics of mastication in pigs

ObjectiveThis study evaluates the effect of unilateral lingual sensory loss on the spatial and temporal dynamics of jaw movements during pig chewing. DesignX-ray Reconstruction of Moving Morphology (XROMM) was used to reconstruct the 3-dimensional jaw movements of 6 pigs during chewing before and after complete unilateral lingual nerve transection. The effect of the transection were evaluated at the temporal and spatial level using Multiple Analysis of Variance. Temporal variables include gape cycle and phase durations, and the corresponding relative phase durations. Spatial variables include the amplitude of jaw opening, jaw yaw, and mandibular retraction-protraction. ResultsThe temporal and spatial dynamics of jaw movements did not differ when chewing ipsilateral versus contralateral to the transection. When compared to pre-transection data, 4 of the 6 animals showed significant changes in temporal characteristics of the gape cycle following the transection, irrespective of chewing side, but the specific response to the lesion was highly dependent on the animal. On the other hand, in affected individuals the amplitude of jaw movements was altered similarly in all 3 dimensions: jaw opening and protraction-retraction increased whereas jaw yaw decreased. ConclusionThe variable impact of this injury in this animal model suggests that individuals use different compensatory strategies to adjust or maintain the temporal dynamics of the gape cycle. Because the amplitude of jaw movements are more adversely affected than their timing, results suggest that maintaining the tongue-jaw coordination is critical and this can come at the expense of bolus handling and masticatory performance.

Shape change throughout the body of the tongue during drinking in the striped skunk (Mephitis mephitis)

In mammals, the tongue plays a central role in many oral behaviors, but it is particularly essential for feeding and drinking. During feeding, the tongue is used for ingestion, manipulation and positioning of food within the oral cavity, and swallowing. When mammals drink, they do so by lapping, licking, or sucking, and the tongue is vital to uptake and transport of fluid into and through the oral cavity and oropharynx. All of these behaviors are performed with only a partial reliance on a bony support system; instead the tongue engages in complex movements as a muscular hydrostat – where selective contraction of intrinsic and extrinsic muscle fibers produce movements and deformations of the tongue. The tongue's anatomical complexity and its location inside the oral cavity make it particularly difficult to visualize and study the movements that contribute to these and other oral behaviors. The objective of this study is to test the ability of marker‐based XROMM (X‐ray reconstruction of moving morphology) to track shape changes throughout the body of the tongue. The striped skunk (Mephitis mephitis), a mammalian omnivore belonging to the order Carnivora, was used as a model for rhythmic lapping while drinking a barium liquid. Data was collected using XROMM with markers implanted in the bones of the skull as well as in the body of the tongue. Tongue markers were used to calculate length changes throughout the body of the tongue. Timing and movement parameters are also registered to the gape cycle derived from the rigid body motions derived from skeletal markers. Based on an analysis of 150 cycles, during rhythmic drinking, the middle and posterior tongue underwent the most variation in length change, while the anterior tongue underwent the least amount of variation in length. In contrast, the posterior tongue underwent the least amount of variation in tongue width, as compared to the anterior and middle tongue. Maximum overall tongue length occurred 2.74±29.3 msec before maximum gape, whereas minimal overall tongue length occurred 20.24±7.38 msec before minimum gape. Based on these preliminary results, this method shows promise for producing quantitative data for studying tongue deformations within the oral cavity. Future studies incorporating spatial parameters of the tongue to the rest of the feeding apparatus across mammals will further our understanding of how the tongue functions during feeding and drinking behaviors.Support or Funding InformationNational Science Foundation Grant DBI‐0922988, National Science Foundation Grant IOS‐1456810This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Variation in human gape cycle kinematics and occlusal topography.

This study tested hypotheses relating intraspecific variation in occlusal morphology and intraspecific variation in jaw movements during feeding. Gape cycle kinematic variation was hypothesized to correlate with gape cycle number within a chewing sequence as well as with food toughness and stiffness. Gape cycle kinematic variation was also hypothesized to correlate with variation in occlusal area, slope, and volume. Twenty-six adult human subjects chewed four foods with varying material properties while their jaw movements were recorded using three-dimensional coordinates of facial markers captured with a Vicon camera system. Post-canine occlusal morphology of each subject was quantified in ArcGIS using dental topographic analysis of dental casts. Gape cycle duration did not vary with gape cycle number, food toughness, or food stiffness. Gape cycle vertical and lateral displacement correlated negatively with gape cycle number, while foods with higher toughness and Young's modulus had greater jaw vertical and lateral displacement. Subjects with steeper occlusal slopes had longer gape cycle durations and greater amounts of vertical displacement during the slow closing phase of the gape cycle. The results suggest that gape cycle durations are relatively consistent despite changes in food properties and gape cycle number, while occlusal slope affects gape cycle duration and vertical displacement during inferred occlusal contact. However, gape cycle number and bolus properties explain greater amounts of kinematic variation than does occlusal morphology.

Sagittal Plane Kinematics of the Jaw and Hyolingual Apparatus During Swallowing in Macaca mulatta.

Studies of mechanisms of feeding behavior are important in a society where aging- and disease-related feeding disorders are increasingly prevalent. It is important to evaluate the clinical relevance of animal models of the disease and the control. Our present study quantifies macaque hyolingual and jaw kinematics around swallowing cycles to determine the extent to which macaque swallowing resembles that of humans. One female and one male adult Macaca mulatta were trained to feed in a primate chair. Videofluoroscopy was used to record kinematics in a sagittal view during natural feeding on solid food, and the kinematics of the hyoid bone, thyroid cartilage, mandibular jaw, and anterior-, middle-, and posterior-tongue. Jaw gape cycles were defined by consecutive maximum gapes, and the kinematics of the swallow cycles were compared with those of the two consecutive non-swallow cycles preceding and succeeding the swallow cycles. Although there are size differences between macaques and humans, and macaques have shorter durations of jaw gape cycles and hyoid and thyroid upward movements, there are several important similarities between our macaque data and human data reported in the literature: (1) The durations of jaw gape cycles during swallow cycles are longer than those of non-swallow cycles as a result of an increased duration of the jaw-opening phase; (2) Hyoid and thyroid upward movement is linked with a posterior tongue movement and is faster during swallow than non-swallow cycles; (3) Tongue elevation propagates from anterior to posterior during swallow and non-swallow cycles. These findings suggest that macaques can be a useful experimental model for human swallowing studies.

Bending Properties of the Jugal Bone in Mallard Ducks and its Significance for Cranial Biomechanics

Few species evolved skulls as derived as ducks and other Anseriform birds, which employ rapid, dexterous movements of the palate and jaws to feed. Despite their exceptional behavior and morphology, little is known about the structure and biomechanics of their jaw muscles, cranial joints, and linkages that facilitate cranial kinesis. In particular, the jugal bone is capable of bending considerably as it links the quadrate and the upper beak. Here we employ a series of methods including microCT imaging, morphometrics, 3D modeling and histology to discover how and why the jugal is capable of such astounding flexibility. Although a narrow suture connects the caudal limb of the jugal with the quadratojugal, flexibility instead appears to occur at narrow regions of the bone. This gross morphology is further complemented by changes to the skeletal tissues that compose the element. Moreover, the orientation of jaw muscle resultants and loading of the skull indicate the jugal experiences a range of loading during different instances of the gape cycle. These findings illustrate the complicated series of adaptations in morphology, histology and biomechanics ducks and other vertebrates employ to engage in derived forms of cranial kinesis and feeding.In birds, cranial kinesis implies the ability to move the upper bill relative to the braincase, contributing to the evolution of the flexible skulls found in birds. The mechanism for elevation of the upper beak consists of a forward movement of the quadrate, exerting force through the jugal and the pterygoid that connect the quadrate to the upper jaw, and elevate the upper beak by bending of the nasofrontal hinge joint and possibly a flexion zone in the jugal. The jugal bone plays a significant role in Mallard feeding as it links the posterior part of the skull with the flexible anterior part of the skull. Interestingly the jugal is quite flexible and when removed from the skull; it is capable of bending 90 degrees while still returning to its original conformation. For the first time, we are studying the biomechanics of birds to determine how their skulls work; while primarily investigating the cause of the flexibility in the jugal bone. We have studied a sample of duck skulls through CT data, 3D modeling, and measurement of cross‐sectional properties of the element. From this data we have found areas of the jugal bone that afford greater consideration in determining the flexibility throughout the jugal bone. This project will create new data about the jugal bone's flexibility, which will contribute to the study of biomechanics of bones and cranial kinesis.