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The development of empathy and positive attitudes are essential elements of professional education. This study explored the nature of empathy and its association with attitudes about, and exposure to older patients in a sample of dental students. Students completed an adapted version of the Jefferson Scale of Physician Empathy (JSPE), the Aging Semantic Differential (ASD) and answered questions about their exposure to older people. Factor analysis was used to identify four factors: (1) Empathy is Valuable, (2) Empathy is Demonstrated, (3) Empathy is not Influential, and (4) Empathy is Difficult to Accomplish. Higher empathy scores were related to the ASD subscale attitude of acceptability of aging and to greater exposure to older adults outside of clinical practice. There were no demographic predictors of higher empathy scores.

This paper is divided into two parts. Part I focuses on the manner in which the components of the face recognition system work together so that a perceiver, within several hundred milliseconds after seeing a familiar face, is able to both identify the face of the perceived and recall elements of the history of past encounters with the perceived. Face recognition plays a crucial role in enabling both human and nonhuman primates to interact in collaborative social groups. This critical function is accomplished through the unidirectional coded transfer of informational elements from one component to another. Although these informational elements themselves are not meaningful to the perceiving agent, they do nevertheless contain essential bits of information that are necessary for the final formation of the meaningful message. The structural components of the system are identified and the manner in which informational elements are coded and transferred sequentially from component to component in the brain of the perceiver is described. The independent, physically separated components in the face recognition system are bridged by an additional component, an “adaptor”, that mediates the transfer of informational elements from one component to another. The nature of the independent systems, and the manner by which the bridging or adaptor apparatus enables coded information transfer from one system to another is discussed. Part II focuses on the analysis of recognition in human-designed sign systems such as Braille and Morse code. Recognition in human-designed sign systems is notable for the stability of the link between sign and meaning. Face recognition is characterized as being subjective, indicating that the meaning of a sign (face) to a perceiver is variable and dependent on context, whereas human-devised sign recognition is characterized as being objective, indicating that the meaning of a sign is context independent and invariant. Human-designed sign systems require the presence in brain of a referent world. An example of a referent world is the set of letters of the alphabet. Representations of this set are installed in the brain through social mediated learning. Human-designed sets of signs (e.g., Braille, and written text) are created to correspond, via a code enabling adaptor structure, to referent worlds in the brain. Human-designed sign systems are the foundations for literacy, a capability only found in humans.

Face recognition depends upon the uniqueness of each human face. This is accomplished by the patterns formed by the unique relationship among face features. Unique face-patterns are produced by the intrusion of random factors into the process of biological growth and development. Processes are described which enable a unique face-pattern to be represented as a percept in the visual sensory system. The components of the face recognition system are analyzed as is the manner in which the precept is connected through microcircuits to a memory file so that the history of a perceiver’s encounters with a familiar face enables the perceiver to access a memory store that is a record of the outcome of past encounters with the perceived. The importance of the face recognition system in enabling humans to individuate members the social group is discussed, as well as the importance of face recognition in the development of the individual’s social identity and ability to be a collaborative member of the social groups to which it belongs. The role of prosopagnosia—the inability to recognize familiar faces—in furthering an understanding of the face recognition system is examined, as is its importance in demonstrating the crucial nature of face recognition in human social functions. It is proposed that human face recognition is not a unique phenomenon but is an elaboration of processes existing in nonhuman primates as well as in lower animals.

Part 1IntroductionThis special issue is an extension of a project begun in 2010 when I sent out a call forpapers forananthology dedicatedto exploringthebiological origins andevolutionarydevelopment of organic mindedness. I expected a dozen or so submissions andreceived over 60. Some of those were published in Origins of Mind (Springer2012), some appear in this special issue and more are forthcoming in a second specialissue dedicated to the topic. It became clear to me that the question of how minded-ness evolved or emerged in the natural world and why is important to researchersacross philosophy and the bio-, neuro-, and medical sciences. What I have aimed todo in the origins of mind project, which includes this special issue, is collect a varietyof novel, thought-provoking, and intuitively plausible accounts of the where, when,why, and how of organic mindedness in the natural world.An important historical fact of the history of philosophy is that the majority of 20thcentury philosophy of mind, dominated as it was by the analytic tradition, enjoyed arobust existence completely insulated from discoveries and insights generated in thebio-, neuro-, and medical sciences. It did, of course, engage with computer science inthat the then reigning philosophy of mind, functionalism, was based on comparisonsbetween machine functionality and human consciousness. Though artificial intelli-gence is an important historical paradigm that has generated insights into whatmindedness might be and what it is not, my own project in philosophy of mind hasbeen to work toward a naturalistic (i.e., consistent with evolutionary theory) accountof organic mindedness that will have implications for medicine, mental and physicalhealth, and our species’ understanding of itself.

Four sequential, sub-processes are identified as the fundamental steps in the processing of signals by big-brained animals. These are, Detection of the signal, its Representation in correlated sensory brain structure, the Interpretation of the signal in another part of the brain and the Expression of the receiver’s response. We label this four-step spatiotemporal process DRIE. We support the view that when the context within which such signals are produced and received is relatively constant, the DRIE process can be ultimately assimilated into the genome, with the Interpretation sub-phase is markedly decreased in duration as speed and efficiency are maximized. With frequent repetition and learning, an analogous result can be attained epigenetically as exemplified in human word and text recognition, allowing tasks critical to primate social function to be accomplished with rapidity and accuracy.

This study was an extension of a previous study that considered dental student attitudes about older adults. In the current study, the association of student interactions with older adults, in both the dental school clinic and daily life, with their attitudes about this group was evaluated using the Aging Semantic Differential. A total of 311 dental students across all four years of academic standing were included in the study. The results showed that students’ interactions with older adults outside the clinic did not relate to positive attitudes; however, even after controlling for the age of the student and the frequency, type of individual, and context of interactions with older adults outside the dental clinic, the number of older adult patients seen in the clinic showed a significant positive relationship with attitudes towards older adults. These results reinforce the conclusions drawn in a previous study that dental students’ general attitudes about older adults may be changed, but that it is the exposure to older adults in a clinical setting that seems to be more critical in shaping these attitudes.

An important inconsistency currently exists in the literature on oral cancer. Reviewing this literature, one finds that the term oral cancer is defined and described with great variation. In a search in PubMed, at least 17 different terms were found for titles of papers reporting data on oral cancer. The variability of the terms used for designating anatomic regions and type of malignant neoplasms for reporting oral cancer has hampered the ability of researchers to effectively retrieve information concerning oral cancer. Therefore, it is sometimes extremely difficult to provide meaningful comparisons among various studies of oral cancer. Recently, a new ontological strategy that is rooted in consensus-based controlled vocabularies has been proposed to improve the consistency of data in dental research (Smith et al. in J Am Dent Assoc 141:1173–1175, 2010). In this paper, we analyzed the terminology dilemma on oral cancer and explained the current situation. We proposed a possible solution to the dilemma using an ontology-based approach. The advantages for applying this strategy are also discussed.

A unique aspect of human communication is the utilization of sets of well-delineated entities, the morphology of which is used to encode the letters of the alphabet. In this paper, we focus on Braille as an exemplar of this phenomenon. We take a Braille cell to be a physical artifact of the human environment, into the structure of which is encoded a representation of a letter of the alphabet. The specific issue we address in this paper concerns an examination of how the code that is embedded in the structure of a Braille cell is transferred with fidelity from the environment through the body and into the Braille reader’s brain. We describe four distinct encoding steps that enable this transfer to occur.

In this paper we address the interrelated questions of why and how certain features of an organism’s environment become meaningful to it. We make the case that knowing the biology is essential to understanding the foundation of meaning-making in organisms. We employ Miguel Nicolelis et al’s seminal research on the mammalian somatosensory system to enrich our own concept of brain-objects as the neurobiological intermediary between the environment and the consequent organismic behavior. In the final section, we explain how brain-objects advance the ongoing discussion of what constitutes a biosemiotic system. In general, this paper acknowledges Marcello Barbieri’s call for biology to make room for meaning, and makes a contribution to that end.

The strong continuity thesis postulates that the properties of mind are an enriched version of the properties of life, and thus that life and mind differ in degree and not kind. A philosophical problem for this view is the ostensive discontinuity between humans and other animals in virtue of our use of symbols—particularly the presumption that the symbolic nature of human cognition bears no relation to the basic properties of life. In this paper, we make the case that a genuine account of strong continuity requires the identification of some sort of correlate of symbol-use in basic life properties. Our strategy is three-fold: 1) we argue that examples of proto-symbolism in simple living systems would be consistent with an evolutionary trajectory that ultimately produced symbolic cognition in humans; 2) we introduce Gordon Tomkins’ biological notion of ‘symbol’ as something that represents to the organism a feature of its environment that is significant to its survival; and 3) we employ this biological understanding of symbol-use to suggest that the symbolic nature of human cognition can be understood as an enriched version of the basic symbolic properties of life, thus preserving life-mind continuity in this context.

Our study considered dental students' general attitudes towards older persons using the Aging Semantic Differential. The influence of age, gender, cohort, education, and academic exposure on general attitudes towards older adults was evaluated using a total of 328 dental students across all four years of academic standing. Students were assessed in the fall and spring semesters. The results showed differential responding on the four subscales, with slight positive ratings on the autonomy, acceptability, and integrity subscales and a slight negative rating for instrumentality. Females expressed more negative attitudes than their male counterparts, with no age differences. There was also no significant impact from a specific, didactic educational component offered to the fourth-year students. However, the fourth-year students were the only group to show positive changes across the full academic year. The results suggest that general attitudes can be changed, but didactic (classroom) forms of education alone are insufficient to meaningfully modify students' perceptions of the elderly. Exposure to older adults in a clinical setting appears to be a critical element, as the fourth-year students received much greater exposure to older patients and more intensified interface with their mentors.

The value of any kind of data is greatly enhanced when it exists in a form that allows it to be integrated with other data. One approach to integration is through the annotation of multiple bodies of data using common controlled vocabularies or ‘ontologies’. Unfortunately, the very success of this approach has led to a proliferation of ontologies, which itself creates obstacles to integration. The Open Biomedical Ontologies (OBO) consortium is pursuing a strategy to overcome this problem. Existing OBO ontologies, including the Gene Ontology, are undergoing coordinated reform, and new ontologies are being created on the basis of an evolving set of shared principles governing ontology development. The result is an expanding family of ontologies designed to be interoperable and logically well formed and to incorporate accurate representations of biological reality. We describe this OBO Foundry initiative and provide guidelines for those who might wish to become involved.

Improving access to dental care for patients experiencing barriers such as financial, transportation, or mental health is a public health concern. Dental schools have an obligation to assist patients experiencing such barriers as well as to educate future dentists and allied professionals on how to assist these patients in overcoming barriers. Once admitted to the dental clinic, retention issues can further complicate the provision of dental care. This article will describe an innovative program designed to address biopsychosocial barriers to dental care. Needs assessments of patients sitting in the waiting room of the dental clinic were conducted by master's of social work (M.S.W.) students. Based on needs assessment results, common dental care barriers were identified and served as the foundation for the establishment of a social work program in the dental clinic. Dental students, faculty, and staff refer patients to the social work program when barriers to care are found. These biopsychosocial barriers are addressed by social workers, uniquely qualified professionals in providing case management, advocacy, referrals, education, and services (CARES). Over the course of three years, 80 percent of patients experiencing an identified barrier to the receipt of dental care were retained through social work intervention. These patients were able to receive dental care within the past year. Dental schools can collaborate with social work schools to establish a protocol and assistance program for dental patients experiencing difficulty accessing care, thereby improving oral health status, retention rates, and dental student education.

Increasing numbers of older people and the decreasing rates of edentulism highlight the importance of dental education that focuses on oral health and aging. This evaluation study assessed dental students' knowledge and beliefs about older people as well as their awareness of the biopsychosocial concerns that are potential barriers to oral health care. Dental students' (N=202) knowledge and perceptions of older people were evaluated before and after the first year of a new educational program. Students completed the Palmore Facts on Aging Quiz II (FAQ II) and answered questions about health problems and social concerns that may influence patient care. The intervention was twofold: 1) the CARES (Counseling, Advocacy, Referral, Education, and Service) Program, a clinical collaboration between the schools of Dental Medicine and Social Work, was initiated; and 2) all students were exposed to geriatric educational interventions. FAQ II scores did not significantly change, but dental students' awareness of mental health, independence, and social concerns increased between Times 1 and 2. The results of the study suggest that positive interactions with older adults by health care providers may depend more on positive perceptions toward older people than increased knowledge about aging. Future research will focus on positive experiences with older adults and attitudes of dental students toward the elderly.

University dental clinic professionals identified increasing numbers of patients with complex problems and generated 2 research questions: (1) Are there significant health and social concerns within the dental clinic population that indicate the need for high-risk screening and social work services?; and (2) How do age, gender, and income influence health and social concerns in this population? This exploratory descriptive cross-sectional study employed a brief self-report survey in a clinic waiting area. Logistic regression was used to understand the influence of age, gender and income on the existence of specific concerns. Results indicate that caregiving, finances and health are issues for 1/3 of the participants and that 44% endorsed 2 or more concerns. These findings were used to develop a routine high-risk screening tool for dental clinic patients and social work services within the clinic; they suggest that community clinics with dental services are an important place for identifying complex unmet needs.

How do we find what is clinically significant in the swarms of data being generated by today's diagnostic technologies? As electronic records become ever more prevalent—and digital imaging and genomic, proteomic, salivaomics, metabalomics, pharmacogenomics, phenomics and transcriptomics techniques become commonplace— different clinical and biological disciplines are facing up to the need to put their data houses in order to avoid the consequences of an uncontrolled explosion of different ways of describing information. Fortunately, a new strategy to advance the consistency of data in the dental research community is emerging. The strategy is based on the idea that existing systems for data collection in dental research will continue to be used, but proposes a methodology in which past, present and future data will be described using a consensus-based controlled structured vocabulary called the Ontology for Dental Research (ODR). The ODR initiative is modeled on a series of existing biomedical ontology projects and will adopt best-practice principles that already have been thoroughly tested in areas such as molecular biology, model organism research, proteomics and genetic disease.1 An “ontology,” in this context, is a controlled, logically structured vocabulary created by experts in a given area as a strategy for promoting consistency in the way primary data (for example, in the form of experimental results or clinical records) are described. Specialist biocurators create “annotations” in the form of HTML tags linking such primary data to expressions in the ontology, thereby making the data available to search and to algorithmic processing. Each ontology contains a taxonomy at its heart, and its logical structure is built around the hierarchy defined by its taxonomic (subtype) relation. But an ontology contains also definitions of its terms, along with additional relations such as parthood, connection and participation, as well as functional relations. These additional relations make the data searchable not only through the use of terms in the ontology, but also through logically related terms. Thus, the ontology can be used to retrieve data associated with terms referring to parts of specific anatomical entities, to anatomical entities immediately connected to specific anatomical entities, or to biological processes in which specific anatomical entities participate. We can conceive ODR, in the first place, as providing an evolving standard set of key words for all aspects of dental research. Initially, these key words can be used to annotate both published literature and existing research databases. Such annotation will enable easier access to research results and allow also first steps toward the semantically enhanced publishing of the future.2 The long-term goals of ODR, however, are much more ambitious. ODR will include not only English-language definitions of its terms for human use and for human quality control of the ontology, but also logical definitions for use by computers. With the latter, ODR then can be used as a computational resource for enhanced search and integration of data, and for reasoning—not only with dental research data but also with data annotated using other biological and bio-medical ontologies with which ODR will be linked logically. The key idea behind ODR is rooted in 10 years of experience using ontologies in support of biomedical research. Ontologies in biomedicine began in the model organism community, which faced a problem of inconsistency in the ways in which the results of functional genomics experiments on different kinds of organisms were being described. To address these problems, a group of leading model organism databases came together in 1999 to create the Gene Ontology (GO), a controlled structured vocabulary for describing different attributes of gene products.3 The GO is designed to be species neutral. It provides a set of some 30,000 common terms for describing different kinds of cellular constituents, biological processes and molecular functions in all kinds of organisms— terms such as “mitochondrion” or “cell division” or “binding.” Since its inception, more than $100 million has been invested in the use of the GO to annotate references to gene products in databases and in the scientific literature. There are more than 11 million annotations relating gene products described in the UniProt, Ensembl and other databases and in more than 50,000 scientific journal articles to terms in the GO.4 The information in huge numbers of dispersed resources is hereby being made accessible through resources such as AmiGO and GOPubMed. Increasingly, the availability of this huge body of integrated information also is having an influence on clinical research, and a simple PubMed search on “gene ontology” reveals a variety of different ways in which the GO and the data annotated in its terms are being used in support of research on human health and disease. Important features of ODR include the following: It will be built to work with the GO and with other high-quality ontologies developed by the biomedical community. This means that ODR will follow the best practices identified through 10 years of testing by the GO and by its sister ontologies participating in the Open Biomedical Ontologies (OBO) Foundry initiative.5 It will be built with terms used by dental researchers, and it will be created and managed by the dental research community itself. The more an ontology is used, the more the ontology and the data described in its terms increase in value, and the more research groups in the future will be motivated to use the ontology in describing their data. The key to ontology success, therefore, is incentivizing users, and to this end it is important that potential users feel that they have ownership of the ontology, that the ontology is populated using the terms that they need and uses definitions that conform to their understanding of these terms. ODR is being initiated by the leading informatician groups within the dental research community in such a way that it will, from the very start, be in a position to serve as an attractor for multiple expanding groups of users whose members will have strong incentives not only to invest resources directed toward ensuring that it is developed in ways that keep pace with scientific advance, but also to recommend it to other users—thereby increasing the value of their own investment in the resource. It can be corrected easily in light of new research discoveries. One key presupposition for the success of an ontology project is its ability to integrate previously annotated data with new terms and relations brought to light by ongoing scientific discovery. This process ensures that previously annotated (legacy) data do not lose their value. To this end, the biomedical ontology community has developed a methodology based on careful versioning of ontologies and annotations, combined with software tools to ensure consistent updating of existing annotation resources with each new version of the ontology. It can be extended easily to incorporate new kinds of data. The organization of OBO ontologies is based on the use of a simple and highly flexible treelike hierarchy structure. This can be extended at will to comprehend new domains of entities as science evolves, and thereby allow the annotation of new kinds of data in ways consistent with existing annotations. The ODR will benefit the research community in a number of ways: It is designed to work well with existing ontologies in all areas of clinical and translation-al science, and thus allows dental research data to be easily integrated with other kinds of data. It is designed to work well with the Semantic Web, providing access to all data resources through unique Web URLs associated with each ontology term.6 It provides a pretested and well-defined set of terms, selections from which can be used in the design of new databases. It can incorporate, where needed, sets of synonyms deriving from legacy term sets and nomenclatures such as the Systematized Nomenclature of Medicine–Clinical Terms and Systematized Nomenclature of Dentistry vocabularies.7,8 To ensure high quality and continued maintenance, the ODR controlled vocabulary will be subject to a process of governance and peer review. Organizations such as the National Institutes of Health are requiring definitions of common standards to ensure that the results obtained through funded research are more easily accessible to external groups. ODR will be created in such a way that its use will meet these common standards. It is designed also to allow information presented in its terms to be usable in satisfying regulatory purposes—submissions to the U.S. Food and Drug Adminis -tration, for example. ORD will contain several subontology components, including the Salivaomics Ontology, 9 a Dental Anatomy Ontology based on the Foundational Model of Anatomy10 and an Oral Pathology Ontology. In addition, vocabulary resources are being developed, based on the Ontology for General Medical Science (OGMS)11 and the Ontology for Biomedical Investigations,12 to represent dental disease and dental procedures, and to allow a seamless connection between the use of ODR in the dental domain and the use of existing ontology resources developed in other areas of medicine. The use of ODR to describe data will be entirely voluntary. However, we anticipate that over time, more and more researchers will see the value of employing a common resource both in annotating their data and, progressively, in designing new databases in which to capture their research results.

Temporomandibular disorders (TMD) are a significant public health problem affecting approximately 5% to 12% of the population.1 TMD is the second most common musculoskeletal condition (after chronic low back pain) resulting in pain and disability.1 Pain-related TMD can impact the individual's daily activities, psychosocial functioning, and quality of life. Overall, the annual TMD management cost in the USA, not including imaging, has doubled in the last decade to $4 billion.1 Patients often seek consultation with dentists for their TMD, especially for pain-related TMD. Diagnostic criteria for TMD with simple, clear, reliable, and valid operational definitions for the history, examination, and imaging procedures are needed to render physical diagnoses in both clinical and research settings. In addition, biobehavioral assessment of pain-related behavior and psychosocial functioning—an essential part of the diagnostic process—is required and provides the minimal information whereby one can determine whether the patient's pain disorder, especially when chronic, warrants further multidisciplinary assessment. Taken together, a new dual-axis Diagnostic Criteria for TMD (DC/TMD) will provide evidence-based criteria for the clinician to use when assessing patients, and will facilitate communication regarding consultations, referrals, and prognosis.2 The research community benefits from the ability to use well-defined and clinically relevant characteristics associated with the phenotype in order to facilitate more generalizable research. When clinicians and researchers use the same criteria, taxonomy, and nomenclature, then clinical questions and experience can be more easily transferred into relevant research questions, and research findings are more accessible to clinicians to better diagnose and manage their patients. The Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) have been the most widely employed diagnostic protocol for TMD research since its publication in 1992.3 This classification system was based on the biopsychosocial model of pain4 that included an Axis I physical assessment, using reliable and well-operationalized diagnostic criteria, and an Axis II assessment of psychosocial status and pain-related disability. The intent was to simultaneously provide a physical diagnosis and identify other relevant characteristics of the patient that could influence the expression and thus management of their TMD. Indeed, the longer the pain persists, the greater the potential for emergence and amplification of cognitive, psychosocial, and behavioral risk factors, with resultant enhanced pain sensitivity, greater likelihood of additional pain persistence, and reduced probability of success from standard treatments.5 The RDC/TMD (1992) was intended to be only a first step toward improved TMD classification, and the authors stated the need for future investigation of the accuracy of the Axis I diagnostic algorithms in terms of reliability and criterion validity—the latter involving the use of credible reference standard diagnoses. Also recommended was further assessment of the clinical utility of the Axis II instruments. The original RDC/TMD Axis I physical diagnoses have content validity based on the critical review by experts of the published diagnostic approach in use at that time and were tested using population-based epidemiologic data.6 Subsequently, a multicenter study showed that, for the most common TMD, the original RDC/TMD diagnoses exhibited sufficient reliability for clinical use.7 While the validity of the individual RDC/TMD diagnoses has been extensively investigated, assessment of the criterion validity for the complete spectrum of RDC/TMD diagnoses had been absent until recently.8 For the original RDC/TMD Axis II instruments, good evidence for their reliability and validity for measuring psychosocial status and pain-related disability already existed when the classification system was published.9–13 Subsequently, a variety of studies have demonstrated the significance and utility of the original RDC/TMD biobehavioral measures in such areas as predicting outcomes of clinical trials, escalation from acute to chronic pain, and experimental laboratory settings.14–20 Other studies have shown that the original RDC/TMD biobehavioral measures are incomplete in terms of prediction of disease course.21–23 The overall utility of the biobehavioral measures in routine clinical settings has, however, yet to be demonstrated, in part because most studies have to date focused on Axis I diagnoses rather than Axis II biobehavioral factors.24 The aims of this article are to present the evidence-based new Axis I and Axis II DC/TMD to be used in both clinical and research settings, as well as present the processes related to their development.

The egg behaves as a prospective cell sustaining the developmental processes of the future embryo. In biosemiotic terms, this apparent teleonomic behaviour can be accounted for without referring to the exclusive causal role played by its genetic makeup. We envision two different processes that are uniquely found in the oocyte: (1) the first involves the mechanisms by which large amounts of mRNA accumulate in the ooplasm to establish the embryo axes prior to fertilization; (2) the second involves transfer of an excess of maternally supplied ribosomes to the oocyte to provide the future embryo with newly synthesized proteins. In this paper, we argue that the information required to sustain embryonic development is not due to any physical properties of the zygotic DNA and the maternal mRNAs, but to their spatially and temporally ordered relationship in the zygote’s internal space.

Abstract Previous investigations have reported a time constant on the order of a few seconds associated with temporal perception in humans, and with movement patterns in humans and other mammalian species. It has been suggested that the time constant represents the operation of a physiological oscillatory mechanism that is common among many mammalian species. However, the time constant has not yet been observed in laboratory animals; therefore, there is no laboratory-based behavior paradigm upon which studies into the physiological nature of this time constant can be based. Because of our familiarity with guinea pig feeding, the current study was undertaken in order to find evidence of the time constant in feeding-associated activities of guinea pigs. Eleven guinea pigs were starved for a 24 hr period, then placed individually into a rich behavioral arena for 30 min, during which time they were videotaped continuously while they roamed freely. The animals inevitably ate during these videotape sessions, and a detailed analysis of chewing parameters was done. It was found that chewing typically occurs in bursts, and that the median burst duration was 1.03 - 3.46 s for individual animals. Chewing burst durations were similar to the durations of many movement patterns in other species including humans. This provides further support for the hypothesis that there is a highly conserved time constant associated with movement patterns in mammals. It is believed that guinea pig chewing bursts provide a convenient laboratory based model for elucidating the neuro-physiologic mechanisms of this time constant.

Human psychophysical studies have provided evidence of a short duration time constant associated with perceptual tasks. This time constant is approximately 3 s in duration, and evidence suggests that it represents a central neural mechanism that functions to integrate “successive events into a Gestalt” in order to create a “subjective present.” Recent studies have found a 3 s time constant in human and chimpanzee movement patterns, suggesting that a similar mechanism subserves both human perceptual and primate motor skills. These studies have focused exclusively on humans and chimpanzees; therefore, it is unclear whether this time constant represents a characteristic derived in the primate order or an ancestral characteristic found in many different mammalian orders. The current study looked for evidence of a 3 s time constant associated with movement patterns in six mammalian species representing three non-primate orders. The results showed that all six species' movement pattern event durations averaged about 3 s, and that there were no significant differences in the mean event durations among the species. Thus, the 3 s time constant originally found in human perceptual and primate motor skills is common among many mammalian orders and probably represents the operation of an ancestral neural mechanism.

Ethology defines action patterns as relatively invariant, species-specific movement patterns. Action patterns are said to have species-specific form features, much like anatomical morphology contains species-specific form features. However, morphology exists in space, whereas movements take form in time. Thus, movements and morphology cannot be quantified in the same way. Standard methods of quantifying the spatial and temporal dimensions of animal movements are not amenable to statistical, cross-species comparative studies. This paper describes a method of quantifying masticatory jaw movements so that rigorous cross-species comparisons can be made. Results show that jaw movements contain species-specific features, many of which are not visually detectable. The results suggest that it is possible to interpret the action pattern definition literally in that masticatory jaw movements have a quantifiable form, which contains species-specific features. Furthermore, the results show that jaw movement forms appear to reflect an animal's phylogenetic history as well as its current feeding niche. Future investigations should be able to elucidate how phylogeny and dietary selection pressures interact to produce specific features of dentoskeletal morphology and masticatory movement form.

This study was an extension of a previous study that considered dental student attitudes about older adults. In the current study, the association of student interactions with older adults, in both the dental school clinic and daily life, with their attitudes about this group was evaluated using the Aging Semantic Differential. A total of 311 dental students across all four years of academic standing were included in the study. The results showed that students' interactions with older adults outside the clinic did not relate to positive attitudes; however, even after controlling for the age of the student and the frequency, type of individual, and context of interactions with older adults outside the dental clinic, the number of older adult patients seen in the clinic showed a significant positive relationship with attitudes towards older adults. These results reinforce the conclusions drawn in a previous study that dental students' general attitudes about older adults may be changed, but that it is the exposure to older adults in a clinical setting that seems to be more critical in shaping these attitudes.

Our study considered dental students' general attitudes towards older persons using the Aging Semantic Differential. The influence of age, gender, cohort, education, and academic exposure on general attitudes towards older adults was evaluated using a total of 328 dental students across all four years of academic standing. Students were assessed in the fall and spring semesters. The results showed differential responding on the four subscales, with slight positive ratings on the autonomy, acceptability, and integrity subscales and a slight negative rating for instrumentality. Females expressed more negative attitudes than their male counterparts, with no age differences. There was also no significant impact from a specific, didactic educational component offered to the fourth-year students. However, the fourth-year students were the only group to show positive changes across the full academic year. The results suggest that general attitudes can be changed, but didactic (classroom) forms of education alone are insufficient to meaningfully modify students' perceptions of the elderly. Exposure to older adults in a clinical setting appears to be a critical element, as the fourth-year students received much greater exposure to older patients and more intensified interface with their mentors.

Dental professionals play a key role in maintaining the well-being of older adults by identifying problems that disturb systemic health. A 3-part instrument was used to assess dental students' knowledge of aging, comfort with patient diversity and patient care strategies (Years 1-4; N= 321). Collaborative education and services were developed by the Schools of Dental Medicine and Social Work. Results indicate that dental students' knowledge ofaging was low (Palmore's FAQ 1 Range = 58%-64%), comfort with geriatric issues improved after the first year of intervention, and strategies for patient care changed with experience. Group differences suggest the importance of utilizing educational “turning points” as teachable moments.

SNODENT is a dental diagnostic vocabulary incompletely integrated in SNOMED-CT. Nevertheless, SNODENT could become the de facto standard for dental diagnostic coding. SNODENT's manageable size, the fact that it is administratively self-contained, and relates to a well-understood domain provides valuable opportunities to formulate and test, in controlled experiments, a series of hypothesis concerning diagnostic systems. Of particular interest are questions related to establishing appropriate quality assurance methods for its optimal level of detail in content, its ontological structure, its construction and maintenance. This paper builds on previous-software-based methodologies designed to assess the quality of SNOMED-CT. When applied to SNODENT several deficiencies were uncovered. 9.52% of SNODENT terms point to concepts in SNOMED-CT that have some problem. 18.53% of SNODENT terms point to SNOMED-CT concepts do not have, in SNOMED, the term used by SNODENT. Other findings include the absence of a clear specification of the exact relationship between a term and a termcode in SNODENT and the improper assignment of the same termcode to terms with significantly different meanings. An analysis of the way in which SNODENT is structurally integrated into SNOMED resulted in the generation of 1081 new termcodes reflecting entities not present in the SNOMED tables but required by SNOMED's own description logic based classification principles. Our results show that SNODENT requires considerable enhancements in content, quality of coding, quality of ontological structure and the manner in which it is integrated and aligned with SNOMED. We believe that methods for the analysis of the quality of diagnostic coding systems must be developed and employed if such systems are to be used effectively in both clinical practice and clinical research.

Improving access to dental care for patients experiencing barriers such as financial, transportation, or mental health is a public health concern. Dental schools have an obligation to assist patients experiencing such barriers as well as to educate future dentists and allied professionals on how to assist these patients in overcoming barriers. Once admitted to the dental clinic, retention issues can further complicate the provision of dental care. This article will describe an innovative program designed to address biopsychosocial barriers to dental care. Needs assessments of patients sitting in the waiting room of the dental clinic were conducted by master's of social work (M.S.W.) students. Based on needs assessment results, common dental care barriers were identified and served as the foundation for the establishment of a social work program in the dental clinic. Dental students, faculty, and staff refer patients to the social work program when barriers to care are found. These biopsychosocial barriers are addressed by social workers, uniquely qualified professionals in providing case management, advocacy, referrals, education, and services (CARES). Over the course of three years, 80 percent of patients experiencing an identified barrier to the receipt of dental care were retained through social work intervention. These patients were able to receive dental care within the past year. Dental schools can collaborate with social work schools to establish a protocol and assistance program for dental patients experiencing difficulty accessing care, thereby improving oral health status, retention rates, and dental student education.

1. We have examined the effects of iontophoretic application of antagonists to excitatory amino acid (EAA) receptors, as well as glycine and gamma-aminobutyric acid (GABA), on rhythmically active (RA) brain stem neurons during cortically induced masticatory activity (RMA) in the anesthetized guinea pig. Ten of these neurons were antidromically activated at latencies of 0.3–0.9 ms by stimulation of the trigeminal motor nucleus (MoV). 2. RA neurons were divided into closer and opener type according to the phase of activation during RMA. Iontophoretic application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a specific non-N-methyl-D-aspartate (NMDA) receptor antagonist, suppressed discharge of both closer and opener type RA neurons during RMA. In contrast, iontophoretic application of 3-((1)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a specific NMDA receptor antagonist, was not effective in suppressing discharge of most opener type RA neurons but did reduce activity of closer type RA neurons. 3. Spike discharge of most RA neurons was time locked to each cortical stimulus during RMA. Some of the RA neurons were activated at a short latency to short pulse train stimulation of the cortex in the absence of RMA. In most cases CNQX reduced such time-locked responses during RMA and greatly reduced discharge evoked by short pulse stimulation of the cortex in all cases. In contrast, CPP was not as effective in suppressing either the time-locked responses during RMA or the discharge evoked by short pulse train stimulation of the cortex. 4. D,L-Homocysteic acid (HCA) application produced low level maintained discharge in RA neurons before RMA induction. When RMA was evoked in combination with HCA, rhythmical burst discharges with distinct interburst periods during the opening phase of RMA were observed in most closer type RA neurons. In contrast, during RMA in combination with HCA application, opener type RA neurons showed burst discharges that were modulated during the RMA cycle but lacked distinct interburst periods during the closer phase of the cycle. 5. During application of strychnine (STR), a glycine antagonist, discharge of closer type RA neurons increased in the opener phase of RMA during continuous HCA application. In contrast, bicuculline methiodide (BIC), a GABA antagonist, did not increase unit discharge of closer type RA neurons in the opener phase of RMA. 6. It is concluded that closer type RA neurons receive, alternatively, EAA-mediated excitatory and glycine-mediated inhibitory masticatory synaptic drive signals during RMA.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Intracellular recording and stimulation were made from guinea pig trigeminal motoneurons (TMNs) in brain stem slices. Electrophysiological properties were examined and the underlying currents responsible for motoneuron excitability were investigated by the use of current clamp and single electrode voltage clamp (SEVC) techniques. 2. The voltage responses to subthreshold hyperpolarizing or depolarizing current pulses showed voltage- and time-dependent inward rectification. SEVC analysis demonstrated that the hyperpolarizing inward rectification resulted from the development of a slowly occurring voltage-dependent inward current activated at hyperpolarized membrane potentials. This current persisted in solutions containing low Ca2+/Mn2+, tetraethylammonium (TEA), and Ba2+, whereas it was reduced by 1–3 mM cesium. The depolarizing inward rectification was mediated by a persistent sodium current (INa-P) that was completely abolished by bath application of tetrodotoxin (TTX). 3. Action potential characteristics were studied by intracellular stimulation with brief current pulses (< 3 ms) in combination with ionic substitutions or application of specific ionic conductance blocking agents. Bath application of TTX abolished the action potential, whereas 1–10 mM TEA or 0.5–2 mM 4-aminopyridine (4-AP) increased, significantly, the spike duration, suggesting participation of the delayed rectifier and A-current type conductances in spike repolarization. SEVC analysis revealed a TEA-sensitive sustained outward current and a fast, voltage-dependent, transient current with properties consistent with their roles in spike repolarization. 4. TMN afterhyperpolarizing potentials (AHPs) that followed a single spike consisted of fast and slow components usually separated by a depolarizing hump [afterdepolarization (ADP)]. The fast component was abolished by TEA or 4-AP but not by Mn2+, Co2+, or the bee venom apamin. In contrast, the slow AHP was readily reduced by Mn2+, Co2+, or apamin, suggesting participation of an apamin-sensitive, calcium-dependent K+ conductance in the production of the slow AHP. SEVC analysis and ionic substitutions demonstrated a slowly activating and deactivating calcium-dependent K+ current with properties that could account for the slow AHP observed in these neurons. 5. Repetitive discharge was examined with long depolarizing current pulses (1 s) and analysis of frequency-current plots. When evoked from resting potential (about -55 mV), spike onset from rheobase occurred rapidly and was maintained throughout the current pulse. At higher current intensities, early and late adaptations in spike discharge were observed. Frequency-current plots exhibited a bilinear relationship for the first interspike interval (ISI) in approximately 50% of the neurons tested and in most neurons tested during steady-state discharge (SS).(ABSTRACT TRUNCATED AT 400 WORDS)

The electromyograph (EMG) activity of the left anterior digastric and the genioglossus muscles was studied in ketamine-anesthetized guinea pigs under 3 separate jaw movement paradigms. The first paradigm has been previously named spontaneous rhythmic jaw movements. These jaw movements occur 1–2 h after the onset of ketamine anesthesia. After spontaneous rhythmic jaw movements began, a single dose of apomorphine caused a new, second jaw movement paradigm to occur, apomorphine-induced rhythmic jaw movements. The final paradigm, cortically-evoked rhythmic jaw movements, was elicited by electrical stimulation of the masticatory area of the cerebral cortex. Genioglossus EMG activity was complex and highly variable in spontaneous rhythmic jaw movements; however, apomorphine-induced jaw movements were characterized by simultaneously occurring rhythmic EMG bursts of approximately 230 ms duration in both the digastric and genioglossus muscles. In 4 of 5 animals, genioglossus muscle activity onset preceded digastric muscle activity onset by approximately 20 ms. These results support the hypothesis that apomorphine-induced rhythmic jaw movements are an analog of lapping in the awake animal. In cortically-evoked rhythmic jaw movements, both digastric and genioglossus EMG activity were time-locked to the cortical electrical stimulation, with an onset latency of approximately 11 ms for the digastric EMG activity and of 16 ms for the genioglossus EMG activity. These results support the hypothesis that both trigeminal and hypoglossal motoneuron pools are closely coupled in certain coordinative movement patterns.

Herpes simplex virus (HSV) infection induces numerous electrophysiological and microscopic changes in neurons in vitro. To investigate the effect of HSV infection on in vivo neuronal activity, we induced an acute, latent and reactivated HSV infection of the trigeminal ganglia of guinea pigs through orofacial HSV inoculation and studied its effect on the trigeminal jaw-opening reflex of anesthetized guinea pigs. During the acute viral infection period both the threshold for elicitation of the reflex, and the latency to the onset of the reflex response were increased. During the latent viral infection in the trigeminal ganglia, the jaw-opening reflexes in the viral infected animals were not different from those of non-infected control animals. However, reactivation of the latent viral infection in these animals resulted in increases in both the threshold and latency of the jaw-opening reflex. These changes were similar to those found in animals with the acute viral infection. These results indicate that acute or reactivated latent HSV infection of the nervous system results in functional changes in the reflex pathways involving the trigeminal gasserian ganglia and brainstem neurons harboring infectious HSV-1.

In the ketamine/urethane anesthetized guinea pig, electromyographic (EMG) responses of the anterior digastric muscle were studied when loci within the lower brainstem were microejected with lidocaine (2%) during rhythmical jaw movements (RJMs) evoked by repetitive electrical stimulation of the masticatory area of the cortex. The area investigated was between the trigeminal motor nucleus (Mot V) and the rostral pole of the inferior olive. Microejections of lidocaine, contralateral to the cortical stimulus site, into the ventral-medial portion of Mot V where digastric motoneurons are known to be located, resulted in reduction or complete abolishment of the digastric EMG activity ipsilateral to the ejection with no effective change in mean cycle duration (CD) or mean percent normalized integrated amplitude of the contralateral digastric EMG. Microejections of lidocaine, contralateral to the cortical stimulus site, into the ponto-medullary reticular formation in areas that included portions of the caudal nucleus pontis caudalis (PnC), nucleus gigantocellularis (GC), medial nucleus parvocellularis (PCRt), and dorsal paragigantocellularis (dPGC), in most cases produced abilateral reduction in the mean normalized integrated amplitude and a bilateral increase in the mean cycle duration. In these sites, the bilateral increase in mean cycle duration of digastric EMG bursts was also associated with a significant increase of coefficient of variation in CD. In many cases, microejection of lidocaine completely abolished rhythmical digastric activity, bilaterally. HRP injections into Mot V were performed to determine the locations of trigeminal premotoneurons and their relationship to effective lidocaine sites for rhythmical jaw movement suppression. Retrogradely labeled cells were found mainly in the mesencephalic nucleus of V; trigeminal principal and spinal V sensory nuclei, bilaterally; and within the intermediate and lateral regions of reticular formation,bilaterally. No labeling was found in the medial reticular formation, including the nucleus gigantocellularis and dorsal paragigantocellularis. The results of this study indicate that regions in the lower brainstem, including portions of the nuclei gigantocellularis and dorsal paragigantocellularis, may participate in masticatory timing and pattern formation, lending further support to the previous hypothesis that (1) both GC and dPGC nuclei of the medial reticular formation contain components of the oscillatory network necessary for RJM production; (2) this regiondoes not contain trigeminal premotoneurons, suggesting a segregation between central timing neurons within these regions of brainstem and trigeminal premotoneurons; and (3) ipsilateral cortex activates neurons located contralaterally within the brainstem reticular core which are critical forbilateral digastric EMG activity during cortically induced RJMs.

The effects of tonic mandibular loading (jaw depression) on spontaneously occurring and apomorphine (APO)-induced rhythmical jaw movements (RJMs) were examined in the anesthetized guinea pig. It was found that this type of perturbation significantly increased only the amplitude and burst duration of the masseter (jaw closer) EMG activity, whereas the frequency of RJMs was not changed. The data suggest that jaw closer muscle spindle or temporomandibular joint feedback does not strongly influence the activity of the neural networks responsible for determining the frequency of RJMs in the anesthetized guinea pig.

The sections in this article are: 1 General Features of Mandibular Motor System 1.1 Muscles of Mandible 1.2 Summary Neuroanatomy of Masticatory System 2 Mastication 2.1 Characteristics of Normal Mastication 2.2 Reflexes Possibly Involved with Chewing 2.3 Evidence Concerning Contribution of Jaw Reflexes to Mastication 2.4 Subcortical Mastication Pattern Generator 3 Initiation and Control of Mandibular Movements 3.1 Role of Sensorimotor Cortex in Mastication and Voluntary Jaw Movements 3.2 Peripheral Systems and Voluntary Isometric Jaw Muscle Contraction 3.3 Trigeminal Relationships in Cerebellum 4 Summary of General Conclusions

We start with the view that the development of systems of symbols is rooted in the regulation of cellular processes and the behavior of unicellular animals. Animals would thereafter start to externalize these internal symbol systems, to coordinate movements with each other. We propose that the brains of multicellular animals can be understood as a continuing elaboration of the early chemical symbol systems of unicellular animals: the labile symbols of the unicellular animal are replaced by hormones, more stable chemical compounds, and nerves that are seen as more stable and more specific routes of activation; and brains developed layers of symbols such that the domain of a symbol is not a set of bodily processes but rather a set of brain processes. Human language is very much in the “style” of the rule-governed symbol manipulation required by all behaving animals, although unique in its complexity. We suggest that the essential question is not how humans have evolved symbolic and linguistic abilities from a primitive sensorimotor brain but rather how do symbols come to exist in biological systems and what is useful and necessary about a system of symbols for the coordination of action within animals and among animals.

The excitability of lingual and inferior dental nerve terminals in the trigeminal main sensory nucleus was increased following a conditioning stimulus delivered to the same nerves of the contralateral side. The lingual nerve primary afferent depolarization (PAD) began at a shorter CS-TS interval (CS, conditioning stimulus; TS, test stimulus), and reached a maximum level of depolarization sooner, than did the PAD evoked in the inferior dental nerve. This difference in the time course of the PAD was not dependent on the site of the CS; i.e. , the same time course was observed for the lingual nerve terminals whether the CS was delivered to either the contralateral lingual, or inferior dental nerve. The effect of the contralateral CS was also tested on the ipsilateral lingual-digastric and inferior dental-digastric reflexes in order to determine if the PAD observed in the ipsilateral nerve terminals would be reflected in similar changes in reflexes mediated by those nerves. It was found that both digastric reflexes were inhibited by the CS. The time course of the inhibition showed similar characteristics to that of the previously discussed PAD; i.e., the onset of the lingual-digastric reflex inhibition began a shorter CS-TS interval and reached maximum effectiveness sooner than did the inhibition of the inferior dental-digastric reflex. The possible significance of the results in relation to the role of presynaptic inhibitory mechanisms in the reflex control of jaw movement is discussed.

Intracellular recordings were obtained from guinea pig trigeminal motoneurons during rhythmic jaw movements. The cells were identified by stimulation of the trigeminal mesencephalic nucleus which evokes excitatory postsynaptic potentials and spikes in jaw-closer motoneurons. The anesthetized guinea pig in the stereotaxic apparatus demonstrated spontaneous rhythmic jaw movements which were characterized by hyperpolarization of jaw-closer motoneurons, occurring concurrently with digastric muscle excitation during the jaw-opening phase of the cycle. The anesthetized guinea pig could also be induced to rhythmically clench and release a stick placed between the molar teeth. During this behavior intracellular recordings in jaw-closer motoneurons revealed a rapid depolarization leading to bursts of action potentials following the hyperpolarization which occurred during the jaw-opening phase of the cycle. The results demonstrate the feasibility of intracellular recording in guinea pig trigeminal motoneurons during rhythmic jaw movements. It was also shown that during the opening phase of the rhythmic jaw movement cycle there is a pronounced hyperpolarization present in the membrane potential of jaw-closer motoneurons. Resolution of the problem of central vs. peripheral origin of this hyperpolarization is significant for our understanding of the motor control of the jaw.

We have investigated the effects of systemic administration of a glycine antagonist, strychnine, on rhythmical jaw movements (RJMs) induced by repetitive stimulation of the masticatory area of the guinea pig cerebral cortex. It was found that after strychnine administration (0.4 mg/kg), the frequency of the cortically induced RJMs was minimally affected, whereas the burst durations of the digastric EMG during the jaw opening phase of the RJM cycle were dramatically increased. These data suggest that the neuronal network (central pattern generator (CPG)) which is responsible for the production of rhythmical jaw movements is not critically dependent upon glycine for the genesis of the basic oscillatory rhythm. On the other hand, glycine synapses are involved with the neuronal mechanisms which are responsible for controlling the burst durations of the digastric muscle during the jaw opening phase of each rhythmic jaw movement cycle.

An excitatory-masseteric reflex response was evoked by electrical gingival stimulation in five subjects; the reflex had an onset latency of 7.6 ms with a SD of 0.7 ms. The response occurred just prior to the silent or inhibitory period. There was consistent post-inhibitory synchronization of the EMG activity record in all subjects. Several methods were used to demonstrate this short-latency reflex. The first was to average non-rectified EMG activity. The second was to increase the number of receptors which are simultaneously activated by using multiple electrodes so that a greater area of gingiva could be stimulated. A third was to increase the level of excitability of the motoneurons in the masseteric pool by increasing voluntary bite force. Fourthly, the excitatory reflex was evoked during increased-excitatory drive to the pool, with the additional feature that the reflex appeared at a time when no ongoing EMG activity was present in the masseter muscle. Little doubt should now remain concerning the existence of a short latency excitatory reflex from intra-oral receptors to masseteric motoneurons in man.

Intracellular recordings were carried out in extensor hindlimb motoneurons during l -DOPA-induced fictive locomotion from acute and chronically spinalized cats. It was demonstrated that motoneurons in chronic animals exhibited irregularly occuring, high frequency discharges within a given burst of a spike train, and sporadic membrane potential depolarizations and hyperpolarizations correlated with extensor and flexor nerve filament activity, respectively, during the locomotor cycle. In contrast, motoneurons recorded from acute cats demonstrated smooth membrane potential fluctuation and regularly occuring low frequency spike discharges. These results indicate that the pharmacologically activated central pattern generator (CPG) for locomotion in young adult chronic cats spinalized at two weeks of age produces disorganized locomotor-like patterns in the absence of sensory feedback. It is suggested that the above-mentioned characteristics of membrane potential fluctuations and spike discharges are not due to alterations in the motoneuron membrane properties, but instead are due to changes in the inputs to the motoneurons.

The ability of l -DOPA and nialamide to produce locomotor-like rhythmic discharges (fictive locomotion) in hind limb nerves of acute and chronically spinalized and paralyzed cats was exmained. Ankle flexor and extensor nerves of chronic cats exhibited pharmacologically induced alternate bursts of activity that had significantly shorter cycle times and burst durations than those produced in ankle flexor and extensor nerves of acutely prepared cats. Furthermore, prior to pharmacologic activation, both ankle flexor and extensor nerves of chronic preparations frequently exhibited spontaneous alternate bursts of activity. Neuronal discharges from nerves of chronic preparations, both prior to and after pharmacologic activation, exhibited much greater variability in both cycle time and burst duration compared with those observed in acute preparations.

Summary During periods of increased presynaptic excitability, antidromic motoneuron activation triggers a centrifugal dorsal root discharge in the cat spinal cord. The present study was concerned with the type of motoneuron and dorsal root fibers involved in this motoneuron-presynaptic interaction as well as with its mechanism. The experiments were carried out in acute spinal cats. By conduction velocity studies it was shown that only alpha motoneurons and primary afferent fibers belonging to group I muscle afferents participate in the interaction. The central time of the motoneuron-presynaptic interaction was approximately 0.4 msec and was always at least 0.2 msec shorter than the monosynaptic reflex. The hypothesis is put forward that via an antidromic electrical interaction, the motoneuron discharge can depolarize the same presynaptic terminals which, through chemical synaptic mechanisms, induce the orthodromic firing of the same neuron.