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Taylor AB, Holmes MA, Laird MF, Terhune CE. Jaw-Muscle Structure and Function in Primates: Insights Into Muscle Performance and Feeding-System Behaviors. Evol Anthropol 2025; 34:e22053. [PMID: 39964129 PMCID: PMC11834762 DOI: 10.1002/evan.22053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2024] [Revised: 11/02/2024] [Accepted: 12/09/2024] [Indexed: 02/21/2025]
Abstract
The jaw-adductor muscles drive the movements and forces associated with primate feeding behaviors such as biting and chewing as well as social signaling behaviors such as wide-mouth canine display. The past several decades have seen a rise in research aimed at the anatomy and physiology of primate chewing muscles to better understand the functional and evolutionary significance of the primate masticatory apparatus. This review summarizes variation in jaw-adductor fiber types and muscle architecture in primates, focusing on physiological, architectural, and behavioral performance variables such as specific tension, fatigue resistance, muscle and bite force, and muscle stretch and gape. Paranthropus and Australopithecus are used as one paleontological example to showcase the importance of these data for addressing paleobiological questions. The high degree of morphological variation related to sex, age, muscle, and species suggests future research should bracket ranges of performance variables rather than focus on single estimates of performance.
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Grants
- P51 OD011132 NIH HHS
- The study was supported by the Emory National Primate Research Center (grant no. ORIP/OD P51OD011132) and the National Science Foundation (grant nos. BCS-0452160, BCS-0552285, BCS-0635649, BCS-0833394, BCS-0962677, BCS-1440516, BCS-1440541, BCS-1440542, BCS-1440545, BCS-1627206, BCS-1719743, BCS-1725925, BCS-1944642, BCS-1944915, BCS-1945767, and BCS-2316863).
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Affiliation(s)
- Andrea B. Taylor
- Department of Foundational Biomedical SciencesTouro University CaliforniaVallejoCaliforniaUSA
| | - Megan A. Holmes
- Department of Family Medicine and Community HealthDuke University School of MedicineDurhamNorth CarolinaUSA
| | - Myra F. Laird
- Department of Basic and Translational Sciences, School of Dental MedicineUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Claire E. Terhune
- Department of AnthropologyUniversity of ArkansasFayettevilleArkansasUSA
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Byron C, Reed D, Iriarte-Diaz J, Wang Q, Strait D, Laird MF, Ross CF. Sagittal suture strain in capuchin monkeys (Sapajus and Cebus) during feeding. AMERICAN JOURNAL OF BIOLOGICAL ANTHROPOLOGY 2023; 180:633-654. [PMID: 36790169 DOI: 10.1002/ajpa.24701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 12/13/2022] [Accepted: 01/16/2023] [Indexed: 05/26/2023]
Abstract
OBJECTIVES Morphological variation in cranial sutures is used to infer aspects of primate feeding behavior, including diet, but strain regimes across sutures are not well documented. Our aim is to test hypotheses about sagittal suture morphology, strain regime, feeding behavior, and muscle activity relationships in robust Sapajus and gracile Cebus capuchin primates. MATERIALS AND METHODS Morphometrics of sinuosity in three regions of the sagittal suture were compared among museum specimens of Sapajus and Cebus, as well as in robust and gracile lab specimens. In vivo strains and bilateral electromyographic (EMG) activity were recorded from these regions in the temporalis muscles of capuchin primates while they fed on mechanically-varying foods. RESULTS Sapajus and the anterior suture region exhibited greater sinuosity than Cebus and posterior regions. In vivo data reveal minor differences in strain regime between robust and gracile phenotypes but show higher strain magnitudes in the middle suture region and higher tensile strains anteriorly. After gage location, feeding behavior has the most consistent and strongest impact on strain regime in the sagittal suture. Strain in the anterior suture has a high tension to compression ratio compared to the posterior region, especially during forceful biting in the robust Sapajus-like individual. DISCUSSION Sagittal suture complexity in robust capuchins likely reflects feeding behaviors associated with mechanically challenging foods. Sutural strain regimes in other anthropoid primates may also be affected by activity in feeding muscles.
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Affiliation(s)
- Craig Byron
- Department of Biology, Mercer University, Macon, Georgia, USA
| | - David Reed
- Department of Oral Biology, University of Illinois, Chicago, Illinois, USA
| | - Jose Iriarte-Diaz
- Department of Biology, University of the South, Sewanee, Tennessee, USA
| | - Qian Wang
- Department of Biomedical Sciences, Texas A&M University College of Dentistry, Dallas, Texas, USA
| | - David Strait
- Department of Anthropology, Washington University in St. Louis, St. Louis, Missouri, USA
- Palaeo-Research Institute, University of Johannesburg, Johannesburg, South Africa
| | - Myra F Laird
- Department of Basic and Translational Sciences, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Callum F Ross
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA
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Panagiotopoulou O, Iriarte-Diaz J, Mehari Abraha H, Taylor AB, Wilshin S, Dechow PC, Ross CF. Biomechanics of the mandible of Macaca mulatta during the power stroke of mastication: Loading, deformation, and strain regimes and the impact of food type. J Hum Evol 2020; 147:102865. [PMID: 32905895 PMCID: PMC7541691 DOI: 10.1016/j.jhevol.2020.102865] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Revised: 07/21/2020] [Accepted: 07/21/2020] [Indexed: 12/26/2022]
Abstract
Mandible morphology has yet to yield definitive information on primate diet, probably because of poor understanding of mandibular loading and strain regimes, and overreliance on simple beam models of mandibular mechanics. We used a finite element model of a macaque mandible to test hypotheses about mandibular loading and strain regimes and relate variation in muscle activity during chewing on different foods to variation in strain regimes. The balancing-side corpus is loaded primarily by sagittal shear forces and sagittal bending moments. On the working side, sagittal bending moments, anteroposterior twisting moments, and lateral transverse bending moments all reach similar maxima below the bite point; sagittal shear is the dominant loading regime behind the bite point; and the corpus is twisted such that the mandibular base is inverted. In the symphyseal region, the predominant loading regimes are lateral transverse bending and negative twisting about a mediolateral axis. Compared with grape and dried fruit chewing, nut chewing is associated with larger sagittal and transverse bending moments acting on balancing- and working-side mandibles, larger sagittal shear on the working side, and larger twisting moments about vertical and transverse axes in the symphyseal region. Nut chewing is also associated with higher minimum principal strain magnitudes in the balancing-side posterior ramus; higher sagittal shear strain magnitudes in the working-side buccal alveolar process and the balancing-side oblique line, recessus mandibulae, and endocondylar ridge; and higher transverse shear strains in the symphyseal region, the balancing-side medial prominence, and the balancing-side endocondylar ridge. The largest food-related differences in maximum principal and transverse shear strain magnitudes are in the transverse tori and in the balancing-side medial prominence, extramolar sulcus, oblique line, and endocondylar ridge. Food effects on the strain regime are most salient in areas not traditionally investigated, suggesting that studies seeking dietary effects on mandible morphology might be looking in the wrong places.
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Affiliation(s)
- Olga Panagiotopoulou
- Department of Anatomy & Developmental Biology, Monash Biomedicine Discovery Institute, Faculty of Medicine Nursing and Health Sciences, Monash University, Clayton, Melbourne, Victoria, 3800, Australia.
| | - Jose Iriarte-Diaz
- Department of Biology, University of the South, Sewanee, TN, 37383, USA
| | - Hyab Mehari Abraha
- Department of Anatomy & Developmental Biology, Monash Biomedicine Discovery Institute, Faculty of Medicine Nursing and Health Sciences, Monash University, Clayton, Melbourne, Victoria, 3800, Australia
| | | | - Simon Wilshin
- Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Herts, AL97TA, UK
| | - Paul C Dechow
- Department of Biomedical Sciences, Texas A&M University College of Dentistry, Dallas, TX, USA
| | - Callum F Ross
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, 60637, USA.
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Ram Y, Ross CF. Jaw Elevator Muscle Coordination during Rhythmic Mastication in Primates: Are Triplets Units of Motor Control? BRAIN, BEHAVIOR AND EVOLUTION 2019; 95:1-14. [PMID: 31821998 PMCID: PMC7101269 DOI: 10.1159/000503890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 10/01/2019] [Indexed: 11/19/2022]
Abstract
The activity of mammal jaw elevator muscles during chewing has often been described using the concept of the triplet motor pattern, in which triplet I (balancing side superficial masseter and medial pterygoid; working side posterior temporalis) is consistently activated before triplet II (working side superficial masseter and medial pterygoid; balancing side posterior temporalis), and each triplet of muscles is recruited and modulated as a unit. Here, new measures of unison, synchrony, and coordination are used to determine whether in 5 primate species (Propithecus verreauxi, Eulemur fulvus, Papio anubis, Macaca fuscata,and Pan troglodytes)muscles in the same triplet are active more in unison, are more synchronized, and are more highly coordinated than muscles in different triplets. Results show that triplet I muscle pairs are active more in unison than other muscle pairs in Eulemur, Macaca, and Papio,buttriplet muscle pairs are mostly not more tightly synchronized than non-triplet pairs. Triplet muscles are more coordinated during triplet pattern cycles than non-triplet cycles, while non-triplet muscle pairs are more coordinated during non-triplet cycles than triplet cycles. These results suggest that the central nervous system alters patterns of coordination between cycles, recruiting triplet muscles as a coordinated unit during triplet cycles but employing a different pattern of muscle coordination during non-triplet cycles. The triplet motor pattern may simplify modulation of rhythmic mastication by being one possible unit of coordination that can be recruited on a cycle-to-cycle basis.
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Affiliation(s)
- Yashesvini Ram
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA
| | - Callum F Ross
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA,
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Taylor AB, Terhune CE, Vinyard CJ. The influence of masseter and temporalis sarcomere length operating ranges as determined by laser diffraction on architectural estimates of muscle force and excursion in macaques (Macaca fascicularis and Macaca mulatta). Arch Oral Biol 2019; 105:35-45. [PMID: 31254839 PMCID: PMC6739116 DOI: 10.1016/j.archoralbio.2019.05.015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Revised: 05/16/2019] [Accepted: 05/18/2019] [Indexed: 11/25/2022]
Abstract
OBJECTIVE Determine sarcomere length (Ls) operating ranges of the superficial masseter and temporalis in vitro in a macaque model and examine the impact of position-dependent variation on Ls and architectural estimates of muscle function (i.e., fiber length, PCSA) before and after Ls-normalization. DESIGN Heads of adult Macaca fascicularis (n = 4) and M. mulatta (n = 3) were bisected postmortem. One side of the jaw was fixed in occlusion, the other in maximum gape. Ls was measured bilaterally using laser diffraction and these measurements were used to estimate sarcomere-length operating ranges. Differences in fiber length and PCSA between sides were tested for significance prior to and following Ls-normalization. RESULTS Sarcomere-length operating ranges were widest for the anterior superficial masseter and narrowest for the posterior temporalis. Compared with other mammals, macaque operating ranges were wider and shifted to the right of the descending limb of a representative length-tension curve. Fibers were significantly stretched by as much as 100%, and PCSAs reduced by as much as 43%, on the maximally gaped compared with occluded sides. Ls-normalization substantially reduced position-dependent variance. CONCLUSIONS The superficial masseter ranges between 87-143% and the temporalis between 88-130% of optimal Ls from maximum gape to occlusion, indicating maximum relative Ls for these macaque muscles exceeds the upper end range previously reported for the jaw muscles of smaller mammals. The wider macaque operating ranges may be functionally linked to the propensity for facially prognathic primates to engage in agonistic canine display behaviors that require jaw-muscle stretch to facilitate production of wide jaw gapes.
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Affiliation(s)
- Andrea B Taylor
- Department of Basic Science, Touro University, Vallejo, CA, United States.
| | - Claire E Terhune
- Department of Anthropology, University of Arkansas, Fayetteville, AR, United States.
| | - Christopher J Vinyard
- Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, OH, United States.
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Liu S, Iriate-Diaz J, Hatsopoulos NG, Ross CF, Takahashi K, Chen Z. Dynamics of motor cortical activity during naturalistic feeding behavior. J Neural Eng 2019; 16:026038. [PMID: 30721881 DOI: 10.1088/1741-2552/ab0474] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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.
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Affiliation(s)
- Shizhao Liu
- Department of Psychiatry, Department of Neuroscience & Physiology, New York University School of Medicine, New York, NY 10016, United States of America. Department of Biomedical Engineering, Tsinghua University, Beijing, People's Republic of China
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