Complex Systems/pt

Depois dos capítulos anteriores, devemos agora ser capazes de reconhecer que, tanto na física moderna como na biologia, um "Sistema Complexo" é um sistema dinâmico multicomponente composto por diferentes subsistemas que normalmente interagem entre si. Tais sistemas são tipicamente estudados através de metodologias de investigação "holísticas" ou como cálculo "total" dos comportamentos dos subsistemas individuais, juntamente com as suas interacções mútuas; estes podem ser descritos analiticamente através de modelos matemáticos, em vez de, de uma forma "redutora" (ou seja, decompondo e analisando o sistema nos seus componentes). Típicos dos Sistemas Complexos, são os conceitos de auto-organização e "Comportamento Emergente"..

Neste capítulo vamos expor alguns conteúdos a favor desta visão mais estocástica e complexa das funções neuromotoras do sistema mastigatório.

 

Article by  Gianni Frisardi

 

Consideração Preliminar

Nos últimos anos, desenvolvimentos paralelos em diferentes disciplinas focaram no que tem sido chamado de "Conectividade", um conceito usado para entender e descrever os "Sistemas Complexos". As conceituações e funcionalizações de conectividade evoluíram amplamente dentro de seus limites disciplinares, mas há claras semelhanças neste conceito e em sua aplicação em todas as disciplinas.. No entanto, qualquer implementação do conceito de conectividade envolve restrições ontológicas e epistemológicas, o que nos leva a questionar se existe um tipo ou conjunto de abordagens de conectividade que poderiam ser aplicadas a todas as disciplinas. Nesta revisão, exploramos quatro desafios ontológicos e epistemológicos no uso da conectividade para entender sistemas complexos do ponto de vista de disciplinas muito diferentes.

No capítulo 'Conectividade e Sistemas Complexos', vamos finalmente introduzir o conceito de:

1. definindo a unidade fundamental para o estudo da conectividade;
2. separando a conectividade estrutural da conectividade funcional;
3. compreensão do comportamento emergente; e
4. medindo a conectividade.

Temos agora que considerar o perfil complexo da função mastigatória, para poder falar em "conectividade"

Somente em tempos posteriores a importância da função mastigatória tornou-se evidente como um Sistema Complexo; fica claro por causa de sua interação com uma infinidade de outros Centros e Sistemas Nervosos (SNC), que também estão distantes do ponto de vista funcional.. A função mastigatória, aliás, sempre foi considerada uma função periférica e isolada no que se refere à fonética e à mastigação.. Seguindo essa interpretação, foram inúmeros os pontos de vista que focaram, e ainda focam, no diagnóstico e reabilitação da mastigação exclusivamente nos maxilares, excluindo qualquer correlação multiestrutural.

Esse tipo de abordagem denota um claro 'reducionismo' nos conteúdos do próprio sistema: em biologia, é mais realista considerar a funcionalidade de sistemas como "Sistemas Complexos" que não operam de forma linear. Esses sistemas empregam uma abordagem estocástica, na qual a interação dos vários constituintes gera um ‘Comportamento Emergente’ (EB) of the same system.

«Nesta abordagem, não basta analisar um único elemento constituinte para interpretar o EB do sistema: é necessário realizar uma análise integrada de todos os componentes constituintes, tanto no tempo quanto no espaço.. »

O resultado paradigmático inverte a tendência de considerar o sistema mastigatório como um simples órgão cinemático, e vai muito além do procedimento mecanicista tradicional da Gnatologia Clássica.

Esse aspecto também introduz um tipo de perfil indeterminístico de funções biológicas, em que a função de um sistema se apresenta como uma rede de múltiplos elementos relacionados. Além de interpretar seu estado, esse sistema deve ser estimulado externamente para analisar a resposta evocada, como é típico de sistemas indeterminísticos.

É, portanto, essencial passar de um modelo simples e linear de clínica odontológica para um modelo de Complexo Estocástico de neurofisiologia mastigatória.

Figura 1: Traço EMG representando um potencial evocado vestibular registrado nos músculos masseteres. Observe que p11 e n21 indicam a latência potencial em 11 e 21 ms do estímulo acústico

Como confirmação desta abordagem mais complexa e integrada para interpretar as funções da mastigação, apresenta-se aqui um estudo onde surge o perfil de um "Sistema Neural Complex". No referido estudo, foi analisada a ligação orgânica e funcional do sistema vestibular com o sistema trigeminal. . Estímulos acústicos podem evocar respostas EMG-reflex no músculo masseter chamadas Potenciais Evocados Miogênicos Vestibulares (VEMPs). Mesmo que esses resultados tenham sido atribuídos anteriormente à ativação dos receptores cocleares (som de alta intensidade), estes também podem ativar os receptores vestibulares. Uma vez que estudos anatômicos e fisiológicos, tanto em animais quanto em humanos, mostraram que os músculos masseteres são alvos das entradas vestibulares, os autores deste estudo reavaliaram a contribuição vestibular para os reflexos massetéricos. Este é um exemplo típico de um sistema complexo de nível básico, pois consiste em apenas dois sistemas nervosos cranianos, mas, ao mesmo tempo, interagindo ativando circuitos mono e polissinápticos. (Figura 1).

Seria apropriado neste momento introduzir alguns tópicos relacionados aos conceitos acima mencionados, que esclareceriam a lógica do projeto Masticationpedia. Isso introduziria os capítulos que estão no centro do projeto.

Assim, o objeto é:

«Mastigação e Processos Cognitivos, bem como Tronco Encefálico e Mastigação
estes serão expandidos em tópicos essenciais adicionais, como a "Segmentação do Sistema Nervoso Trigêmeo" no último capítulo, 'Ciência Extraordinária'.»

Mastigação e Processos Cognitivos

In recent years, mastication has been a topic of discussion about the maintenance and support effects of cognitive performance.

An elegant study performed through _fMR and positron emission tomography (PET) has shown that mastication leads to an increase in cortical blood flow and activates the additional somatosensory cortex, motor motor and insular, as well as the striatum, the thalamus, and the cerebellum. Mastication right before performing a cognitive task increases oxygen levels in the blood (BOLD of the fMRI signal) in the prefrontal cortex and the hippocampus, important structures involved in learning and memory, thereby improving the performance task. Previous epidemiological studies have shown that a reduced number of residual teeth, incongruous use of prosthetics, and a limited development of the mandibular force are directly related to the development of dementia, further supporting the notion that mastication contributes to maintaining cognitive functions..

A recent study has provided further evidence in support of the interaction between masticatory processes, learning and memory, focusing on the function of the hippocampus that is essential for the formation of new memories. An occlusal disharmony, such as loss of teeth and increases in the vertical occlusal dimension, causes bruxism or pain to the mastication muscles and temporomandibular disorders (TMDs). Hence, to describe the impaired function of the hippocampus in a reduced situation or abnorme masticatory function, the authors employed an animal model (mice) called ‘Molarless Senescence-Accelerated Prone’ (SAMP8) in order to make a parallelism on man. In SAMP8 mice, to which the occlusion was modified, increasing the occlusal vertical dimension of about 0.1 mm with dental materials showed that the occlusal disharmony disrupts learning and memory. These animals showed an age-dependent deficit in space learning at Morris’s water. 

Increasing the vertical dimension of the bite in SAMP8 mice decreases the number of pyramidal cells and the numbers of their dendritic spines. It also increases the hypertrophy and hyperplasia fibrillar protein acid in astrocytes in the regions of the CA1 and CA3 hippocampus.. In rodents and monkeys, occlusal disharmonies induced through an increase in the vertical dimension with acrylic increases on the incisors or the insertion of bite-plane in the jaw are associated with increased urinary cortisol levels and elevated plasma levels of corticosterone, suggesting that occlusal disharmony is also a source of stress.

In support of this notion, SAMP8 mice with learning deficits show a marked increase in the plasma levels of corticosterone and subregulation of GR and GRmRNA of the hippocampus. The occlusal disharmony also affects catecholaminergic activity. Alternating the closure of the bite by inserting an acrylic bite-plane on the lower incisors leads to an increase in levels of dopamine and noradrenaline in the hypothalamus and the frontal cortex, and decreases in thyroxinaydroxylase, GTP cyclohydrochloride, and immunoreactive serotonin in the cerebral cortex and the caudate nucleus, in the nigra substance, in the locus ceruleus, and in the dorsal raphe nucleus, which are similar to chronic stress-induced changes. These changes in the catecolaminergic and serotonergic systems, induced by occlusal disharmonies, clearly affect the innervation of the hippocampus. The conditions of increasing the vertical dimension alter neurogenesis and lead to apoptosis in the ippocampal gyrus by decreasing the expression of the ippocampal brain derived from neurotrophic factors: all this could contribute to the changes in observed learning in animals with occlusal disharmony.

Brainstem and Mastication

Figure 2: Segmentation of Trigeminal Nervous System

The brainstem district is a relay area that connects the upper centres of the brain, the cerebellum, and the spinal cord, and provides the main sensory and motor innervation of the face, head, and neck through the cranial nerves.

This plays a determining role in regulation of respiration, locomotion, posture, balance, excitement (including intestinal control, bladder, blood pressure, and heart rate). It is responsible for regulating numerous reflexes, including swallowing, coughing, and vomiting. The brainstem is controlled by higher Cerebral Centers from cortical and subcortical regions, including the Basal Ganglia Nuclei and Diencephal, as well as feedback loops from the cerebellum and spinal cord. Neuromodulation can be achieved by the ‘classical’ mode of glutammatergic neurotransmitters and GABA (gamma-amino butyric acid) through a primary excitation and inhibition of the ‘anatomical network’, but can also be achieved through the use of transmitters acting on G-proteins. These neuromodulators include the monoamine (serotonine, noradrenaline, and dopamine) acetylcholine, as also glutamate and GABA. In addition, not only do neuropeptides and purines act as neuromodulators: so do other chemical mediators too, like Growth Factors which might have similar actions.

The neural network described above does not end with the only correlation between trigeminal somatosensory centres and other motor areas but also strays into the amigdaloidei processes through a correlation with the trigeminal brainstem area. The amygdala becomes active from fear, playing an important role in the emotional response to life-threatening situations. When lab rats feel threatened, they respond by biting ferociously. The force of the bite is regulated by the motor nuclei of the trigeminal system and trigeminal brainstem Me5.The Me5 transmits proprioceptive signals from the Masticatory muscles and parodontal ligaments to trigeminal nuclei and motors. Central Amygdaloid Nucleus (ACe) projections send connections to the trigeminal motor nucleus and reticular premotor formation and directly to the Me5.

To confirm this, in a study conducted among mice, the neurons in the Central Amigdaloide nucleus (ACe) were marked after the injection of a retrograde tracer(Fast Blue), in the caudal nucleus of the Me5, indicating that the Amigdaloians send direct projections to the Me5, and suggest that the amygdala regulates the strength of the bite by modifying the neuronal activity in the Me5 through a neural facilitation.

Modifying occlusal ratios can alter oral somatosensory functions and the rehabilitative treatments of the Masticatory system should restore somatosensory functions. However, it is unclear why some patients fail to adapt to the masticatory restoration, and sensomotor disorders remain. At first, they would seem to be structural changes, not just functional ones. The primary motor cortex of the face is involved in the generation and control of facial gold movements and sensory inputs or altered motor functions, which can lead to neuroplastic changes in the M1 cortical area.

Conclusive Considerations

In conclusion, it is clear from the premise, that the Masticatory system should be considered not certainly as a system simply governed by mechanical laws, but as a "Complex System" of indeterministic type, where one can quantify the "Emerging Behavior" only after stimulating it and then analysing the response evoked (Figure 2). The Neuronal System also dialogues with its own encrypted machine language (potential action and ionic currents) and, therefore, it is not possible to interpret the symptoms referred to by the patient through natural language.

This concept deepens knowledge of the state of health of a system because it elicits an answer from inside the network — or, at least, from a large part of it — by allocating normal and/or abnormal components of the various nodes of the network. In scientific terms, it also introduces a new paradigm in the study of the Masticatory System: the "Neuro Gnathology Function", that we will meet in due course in the chapter ‘Extraordinary Science’.

Currently, the interpretation of the Emergent Behavior of the Mastication system in dentistry is performed only by analysing the voluntary valley response, through electromyographic recordings ‘EMG interference pattern’, and radiographic and axographic tests (replicators of mandibular movements). These can only be considered descriptive tests.

The paradigm of gnathological descriptive tests faced a crisis years ago: despite an attempt to reorder the various axioms, schools of thought, and clinical-experimental strictness in the field of Temporomandibular Disorders (through the realization of a protocol called "Research Diagnostic Criteria" RDC/TMDs), this paradigm has not yet come to be accepted because of the scientific-clinical incompleteness of the procedure itself. It deserves, however, a particular reference to the RDC/TMD, at least for the commitment that was carried out by the authors and, at the same time, to scroll the limits.

The RDC/TMD protocol was designed and initialized to avoid the loss of ‘standardized diagnostic criteria’ and evaluate a diagnostic standardization of empirical data at disposition. This protocol was supported by the National Institute for Dental Research (NIDR) and conducted at the University of Washington and the Group Health Corporative of Puget Sound, Seattle, Washington. Samuel F. Dworkin, M. Von Korff, and L. LeResche were the main investigators.

To arrive at the formulation of the protocol of the ‘RDC’, a review of the literature of diagnostic methods in rehabilitative dentistry and TMDs, and subjected to validation and reproducibility, has been made. Taxonomic systems were taken into account by Farrar (1972), Eversole and Machado (1985), Bell (1986), Fricton (1989), American Academy of Craniomandibular Disorders (AACD) (1990), Talley (1990), Bergamini and Prayer-Galletti (1990), Truelove (1992), and compared them by granting them to a set of assessment criteria. The evaluation criteria were split into two categories that involve methodological considerations and clinical considerations.

The end of the research came to the elimination, due to a lack of scientific and clinical validation, of a series of instrumental diagnostic methodologies like interferential electromyography (EMG Interference Pattern), Pantography, X-ray diagnostics, etc. These will be described in more detail in the next editions of Masticationpedia. This first target was, therefore, the scientific request of an "objective data"' and not generated by opinions, schools of thought or subjective evaluations of the phenomenon’. During the Workshop of the International Association for Dental Research (IADR) of 2008, preliminary results of the RDC/TMDs were presented in the endeavour to validate the project.

The conclusion was that, to achieve a review and simultaneous validation of [RDC/TMD], it is essential that the tests should be able to make a differential diagnosis between TMD patients with pain and subjects without pain, and above all, discriminate against patients with TMD pain from patients with orofacial pain without TMD.

This last article, reconsidering pain as an essential symptom for the clinical interpretation, puts all the neurophysiological phenomenology in the game, not just this. To move more easily at ease in this medical branch, a different scientific-clinical approach is required, one that widens the horizons of competence in fields such as bioengineering and neurobiology.

It is, therefore, essential to focus attention on how to take trigeminal electrophysiological signals in response to a series of triggers evoked by an electrophysiological device, treating data and determining an organic-functional value of the trigeminal and masticatory systems as anticipated by Marom Bikson and coll. in their «Electrical stimulation of cranial nerves in cognition and disease».

We should think of a system that unifies the mastication and neurophysiological functions by introducing a new term: "Neuro-Gnathological Functions"
which will be the object of a dedicated chapter.

Bibliography & references

Masticationpedia is a charity, a not-for-profit organization operating in dentistry medical research,
particularly focusing on the field of the neurophysiology of the masticatory system
 

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