RESUMO
Ion channels are pores formed by proteins and responsible for carrying ion fluxes through cellular membranes. The ion channels can assume conformational states thereby controlling ion flow. Physically, the conformational transitions from one state to another are associated with energy barriers between them and are dependent on stimulus, such as, electrical field, ligands, second messengers, etc. Several models have been proposed to describe the kinetics of ion channels. The classical Markovian model assumes that a future transition is independent of the time that the ion channel stayed in a previous state. Others models as the fractal and the chaotic assume that the rate of transitions between the states depend on the time that the ionic channel stayed in a previous state. For the calcium activated potassium channels of Leydig cells the R/S Hurst analysis has indicated that the channels are long-term correlated with a Hurst coefficient H around 0.7, showing a persistent memory in this kinetic. Here, we applied the RS analysis to the opening and closing dwell time series obtained from simulated data from a chaotic model proposed by L. Liebovitch and T. Tóth [J. Theor. Biol. 148, 243 (1991)] and we show that this chaotic model or any model that treats the set of channel openings and closings as independent events is inadequate to describe the long-term correlation (memory) already described for the experimental data.
Assuntos
Potenciais de Ação/fisiologia , Ativação do Canal Iônico/fisiologia , Células Intersticiais do Testículo/fisiologia , Potenciação de Longa Duração/fisiologia , Modelos Biológicos , Dinâmica não Linear , Canais de Potássio Cálcio-Ativados/fisiologia , Animais , Células Cultivadas , Simulação por Computador , Retroalimentação/fisiologia , Masculino , CamundongosRESUMO
The importance of knee position for bodily stability is described by some authors, however Biodex Stability System (BSS) trials have not been used to assess the reliability and effects of different knee positions. The purposes of this study were to test the reliability of BSS indices using two knee positions in the measurement protocol (either permitting slight knee flexion or maintaining them locked in total extension) and to compare the BSS indices between these two knee positions. The measurements were taken of the Overall Stability Index (OSI), Anterior-Posterior Stability Index (APSI) and Medial-Lateral Stability Index (MLSI) during a 30s protocol which gradually and automatically increased in difficulty among 21 healthy female subjects (22.8+/-1.0 years old). The subjects performed four trials which, without visual feedback, permitted knee flexion as well as four trials which did not, in a randomized order. The first two trials in each set were used for familiarization only. Permitting slight flexion yielded better reliability results (OSI Intra-class Correlation Coefficient [ICC]=0.93, APSI ICC=0.90, MLSI ICC=0.89) than maintaining the knee in total extension (OSI ICC=0.88, APSI ICC=0.87, MLSI ICC=0.79), with good agreement in the Bland and Altman test. Moreover, permitted knee flexion in BSS presented better balance stability values for OSI (P=0.001) and APSI (P=0.024), however the MLSI did not present significant difference between positions (P=0.345).
Assuntos
Joelho/fisiologia , Equilíbrio Postural/fisiologia , Retroalimentação/fisiologia , Feminino , Humanos , Articulação do Joelho/fisiologia , Reprodutibilidade dos Testes , Adulto JovemRESUMO
The purpose of this study was to investigate whether the additional sensory information could improve postural control in individuals with unilateral anterior cruciate ligament (ACL) injury. Twenty-eight individuals with unilateral ACL injury (mean age 23.6, 26 males, 2 females) and 28 healthy young control subjects (mean age 22.1 years, 26 males, 2 females) participated in this study. Postural control was evaluated with subjects single-leg standing on a force platform with eyes closed under two sensory conditions: normal sensory information and light touch to a stationary bar (applied force below 1N). Three trials of 30s were performed in each single-leg stance and in each sensory condition. Mean sway amplitude and predominant frequency of center of pressure were calculated for both anterior-posterior and medial-lateral directions. Individuals with ACL injury showed greater mean sway amplitude than healthy control individuals even though the predominant frequency was similar for both groups. Additional sensory information improved postural control performance in individuals with ACL injury and healthy control, with a greater effect observed for the ACL group. Based on these results, we suggest that reduction in postural control performance in individuals with ACL injury would be due to the reduction of sensory information provided by the ACL, but when sensory information is enhanced, postural control performance improves. These results have implications for novel approaches to improve stability in individuals with ACL injury.
Assuntos
Lesões do Ligamento Cruzado Anterior , Ligamento Cruzado Anterior/fisiopatologia , Retroalimentação , Traumatismos do Joelho/fisiopatologia , Equilíbrio Postural , Distúrbios Somatossensoriais/fisiopatologia , Adolescente , Adulto , Ligamento Cruzado Anterior/inervação , Sinais (Psicologia) , Retroalimentação/fisiologia , Feminino , Humanos , Traumatismos do Joelho/complicações , Traumatismos do Joelho/patologia , Masculino , Equilíbrio Postural/fisiologia , Propriocepção/fisiologia , Privação Sensorial/fisiologia , Distúrbios Somatossensoriais/etiologia , Distúrbios Somatossensoriais/reabilitação , Tato/fisiologiaRESUMO
Abnormal sensory processing seems to be involved in hyperhidrosis. To test this hypothesis, we investigated tactile acuity and cortical plastic changes in patients with primary hyperhidrosis (PH) and their asymptomatic relatives. We studied thirteen subjects belonging to two families with PH and thirteen age-matched healthy controls using Johnson-Van Boven-Phillips domes before and after 45min of transient visual deafferentation. Spatial discrimination thresholds (SDTs) were lower in controls than in the familial group (1.08+/-0.25 vs 1.59+/-0.71; p=0.0032). After 45min of light deprivation and blindfolding, SDTs decreased significantly in controls (0.83+/-0.3; p=0.003), but not in patients (1.4+/-0.62; p=0.108). Interestingly, two subjects without clinical complaints of hyperhidrosis had abnormal SDTs behavior after short term visual deprivation. This study demonstrates that sensory processing is abnormal in PH, with a lack of plastic cortical somatosensory changes regardless of clinical condition. These modulatory abnormalities would affect gating processes in the somatosensory cortex which may play a role in maintaining hyperhidrosis.
Assuntos
Hiperidrose/complicações , Hiperidrose/genética , Plasticidade Neuronal/genética , Transtornos da Percepção/genética , Transtornos da Percepção/fisiopatologia , Tato/genética , Adolescente , Adulto , Sinais (Psicologia) , Análise Mutacional de DNA , Retroalimentação/fisiologia , Feminino , Testes Genéticos , Genótipo , Humanos , Masculino , Pessoa de Meia-Idade , Inibição Neural/genética , Exame Neurológico , Testes Neuropsicológicos , Linhagem , Transtornos da Percepção/diagnóstico , Estimulação Física , Privação Sensorial/fisiologia , Limiar Sensorial/fisiologia , Córtex Somatossensorial/fisiopatologia , Percepção Espacial/fisiologia , Percepção Visual/fisiologiaRESUMO
INTRODUCTION: In the last decades, the scientific study of consciousness in the scope of the cognitive neurosciences can be considered one of the greatest challenges of contemporary science. The Gerald Edelman theory of consciousness is one of the most promising and controversial perspectives. This theory stands out by its approach to topics usually rejected by other neurophysiologic theories of consciousness, as the case of the neurophysiologic explanation of qualia. AIM: The goal of this paper is to review the dynamic core theory of consciousness, presenting the main features of the theory, analyzing the explanation strategies, their empirical extensions, and elaborating some critical considerations about the possibility of the neuroscientific study of qualia. DEVELOPMENT: The central and additional theoretical components are analyzed, emphasizing its ontological, restrictive and explanatory assumptions. The properties of conscious phenomena and their cerebral correlates as advanced by the theory are described, and finally its experiments and empirical extensions are examined. The explanatory strategies of the theory are analyzed, based on conceptual isomorphism between the phenomenological properties and the neurophysiological and mathematical measures. Some criticisms could be raised about the limitations of the dynamic core theory, especially regarding its account of the so-called 'hard problem' of consciousness or qualia.
Assuntos
Encéfalo/fisiologia , Estado de Consciência/fisiologia , Modelos Neurológicos , Modelos Psicológicos , Percepção/fisiologia , Animais , Encéfalo/citologia , Encéfalo/crescimento & desenvolvimento , Sobrevivência Celular , Córtex Cerebral/fisiologia , Eletroencefalografia , Retroalimentação/fisiologia , Humanos , Aprendizagem/fisiologia , Memória/fisiologia , Rede Nervosa/fisiologia , Plasticidade Neuronal , Neurônios/fisiologia , Esquizofrenia/fisiopatologia , Sensação/fisiologia , Tálamo/fisiologiaRESUMO
Previous research has demonstrated that suppression of inhibition in projection neurons of the basolateral complex of the amygdala (BLA) represents an essential mechanism underlying the emergence of negative emotional responses, including exaggerated fear and anxiety. The present work evaluates inhibitory postsynaptic potentials (IPSPs) in pyramidal projection neurons of the BLA in rats subjected to either diazepam or ethanol withdrawal or uncontrollable stress. These are experimental paradigms conducive to a negative emotional state. In slices containing the BLA, IPSPs were studied using whole-cell patch clamp. In control animals, a small IPSP was evoked by sub-threshold stimulation of the external capsule. When an action potential (AP) was evoked by supra-threshold stimuli, IPSPs were considerably larger; these IPSPs were sensitive to blockade of GABA(A) receptors by picrotoxin. However, IPSPs were clearly reduced in diazepam- or ethanol-withdrawn and in stressed rats. Firing of an AP by a depolarizing pulse applied through the patch pipette consistently evoked an inhibitory postsynaptic current (IPSC) in the pyramidal neurons of control animals from all three experimental models; these IPSCs were mediated by GABA(A) receptor activation and were blocked after suppression of glutamatergic transmission. In contrast, no IPSCs were observed in slices from diazepam- or ethanol-withdrawn or stressed animals, although the depolarizing pulse regularly evoked an AP in pyramidal neurons. It is concluded that, in withdrawn or stressed rats, GABAergic disinhibition occurs due to attenuation or suppression of feedback inhibition.
Assuntos
Tonsila do Cerebelo/fisiopatologia , Hipnóticos e Sedativos/efeitos adversos , Estresse Psicológico/fisiopatologia , Síndrome de Abstinência a Substâncias/fisiopatologia , Animais , Depressores do Sistema Nervoso Central/efeitos adversos , Diazepam/efeitos adversos , Estimulação Elétrica , Eletrofisiologia , Etanol/efeitos adversos , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Retroalimentação/fisiologia , Masculino , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Restrição Física , Ácido gama-Aminobutírico/fisiologiaRESUMO
BACKGROUND: Structure identification of dynamic models for complex biological systems is the cornerstone of their reverse engineering. Biochemical Systems Theory (BST) offers a particularly convenient solution because its parameters are kinetic-order coefficients which directly identify the topology of the underlying network of processes. We have previously proposed a numerical decoupling procedure that allows the identification of multivariate dynamic models of complex biological processes. While described here within the context of BST, this procedure has a general applicability to signal extraction. Our original implementation relied on artificial neural networks (ANN), which caused slight, undesirable bias during the smoothing of the time courses. As an alternative, we propose here an adaptation of the Whittaker's smoother and demonstrate its role within a robust, fully automated structure identification procedure. RESULTS: In this report we propose a robust, fully automated solution for signal extraction from time series, which is the prerequisite for the efficient reverse engineering of biological systems models. The Whittaker's smoother is reformulated within the context of information theory and extended by the development of adaptive signal segmentation to account for heterogeneous noise structures. The resulting procedure can be used on arbitrary time series with a nonstationary noise process; it is illustrated here with metabolic profiles obtained from in-vivo NMR experiments. The smoothed solution that is free of parametric bias permits differentiation, which is crucial for the numerical decoupling of systems of differential equations. CONCLUSION: The method is applicable in signal extraction from time series with nonstationary noise structure and can be applied in the numerical decoupling of system of differential equations into algebraic equations, and thus constitutes a rather general tool for the reverse engineering of mechanistic model descriptions from multivariate experimental time series.
Assuntos
Algoritmos , Retroalimentação/fisiologia , Modelos Biológicos , Análise Numérica Assistida por Computador , Linguagens de Programação , Software , Simulação por ComputadorRESUMO
Echolocating insectivorous bats consummate prey captures using a distinct vocal motor pattern commonly known as the terminal or feeding buzz, which is widely considered a fixed motor pattern executed independently of auditory feedback influences. The Mexican free-tailed bat, Tadarida brasiliensis, offers an opportunity to explore the role of sensory feedback in buzzing because they emit similar buzzes both in flight during foraging and while stationary as communication sounds. Here we compared the spectral and temporal patterns of foraging and communication buzzes to address whether or not auditory feedback may influence buzz patterns. We found that while foraging buzzes uttered in open space were composed of generic FM calls, communication buzzes were composed of an adapted CF-FM call similar to the call type used by T. brasiliensis when navigating in confined spaces. This provides the first evidence that some bats can make significant context-dependent changes in the spectral parameters of calls within their buzz. We also found that inter-pulse intervals, but not call durations, were different within the two buzz types. These observations indicate that though a common pattern generator hierarchically organizes all buzzes, T. brasiliensis retains a significant capacity to adapt the spectral and temporal patterns of elements within its buzzes.
Assuntos
Comunicação Animal , Quirópteros/fisiologia , Comportamento Alimentar/fisiologia , Vocalização Animal/fisiologia , Animais , Comportamento Animal/fisiologia , Ecolocação/fisiologia , Retroalimentação/fisiologia , Feminino , MasculinoRESUMO
Rats, people, and many other omnivores eat in meals rather than continuously. We show by experimental test that eating in meals is regulated by a simple bang-bang control system, an idea foreshadowed by Le Magnen and many others, shown by us to account for a wide range of behavioral data, but never explicitly tested or tied to neurophysiological facts. The hypothesis is simply that the tendency to eat rises with time at a rate determined by satiety signals. When these signals fall below a set point, eating begins, in on-off fashion. The delayed sequelae of eating increment the satiety signals, which eventually turn eating off. Thus, under free conditions, the organism eats in bouts separated by noneating activities. We report an experiment with rats to test novel predictions about meal patterns that are not explained by existing homeostatic approaches. Access to food was systematically but unpredictably interrupted just as the animal tried to start a new meal. A simple bang-bang model fits the resulting meal-pattern data well, and its elements can be identified with neurophysiological processes. Hypothalamic inputs can provide the set point for longer-term regulation carried out by a comparator in the hindbrain. Delayed gustatory and gastrointestinal aftereffects of eating act via the nucleus of the solitary tract and other hindbrain regions as neural feedback governing short-term regulation. In this way, the model forges real links between a functioning feedback mechanism, neuro-hormonal data, and both short-term (meals) and long-term (eating-rate regulation) behavioral data.
Assuntos
Apetite/fisiologia , Retroalimentação/fisiologia , Comportamento Alimentar/fisiologia , Hipotálamo/fisiologia , Modelos Biológicos , Resposta de Saciedade/fisiologia , Animais , Simulação por Computador , Inibição Neural/fisiologia , RatosRESUMO
We investigated the speed-accuracy trade-off in a task of pointing with the big toe of the right foot by a standing person that was designed to accentuate the importance of postural adjustments. This was done to test two hypotheses: (1) movement time during foot pointing will scale linearly with ID during target width changes, but the scaling will differ across movement distances; and (2) variations in movement time will be reflected in postural preparations to foot motion. Ten healthy adults stood on the force plate and were instructed to point with the big toe of the right foot at a target (with widths varying from 2 to 10 cm) placed on the floor in front of the subject at a distance varying from 10 to 100 cm. The instruction given to the subjects was typical for Fitts' paradigm: "be as fast and as accurate as possible in your pointing movement". The results have shown that movement time during foot pointing movements scaled with both target distance (D) and target width (W), but the two dependences could not be reduced to a single function of W/D, confirming the first hypothesis. With respect to the second hypothesis, we found that changes in task parameters led to proportional variations in movement speed and indices of variability of the postural adjustments prior to leg movement initiation, confirming the second hypothesis. Both groups of observations were valid over the whole range of distances despite the switch of the movement strategy in the middle of this range. We conclude that the speed-accuracy trade-off in a task with postural adjustments originates at the level of movement planning. The different dependences of movement time on D and W may be related to spontaneous postural sway (migration of the point of application of the resultant force acting on the body of the standing person). The results may have practical implications for posture and gait rehabilitation techniques that use modifications of stepping accuracy.
Assuntos
Retroalimentação/fisiologia , Pé/fisiologia , Destreza Motora/fisiologia , Movimento/fisiologia , Equilíbrio Postural/fisiologia , Tempo de Reação/fisiologia , Adulto , Marcha/fisiologia , Transtornos Neurológicos da Marcha/fisiopatologia , Humanos , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Testes Neuropsicológicos , Fatores de Tempo , Caminhada/fisiologiaRESUMO
Optimum operation and automatic control of large-scale solid substrate fermentation (SSF) bioreactors is difficult. Though advanced control algorithms can handle most challenges encountered properly, for real-time SSF processes such controllers are expensive and time consuming to design and tune. With these considerations, advanced control algorithm tests using realistic simulations appear more appropriate. We used a phenomenological process model of an SSF pilot bioreactor, coupled with a realistic noise model, to test linear model predictive controllers. We focused on the effect noise has on the performance of the control algorithms, and how to enhance performance using a combination of low-pass (Butterworth) and outlier shaving (Hampel) filters. In simulations undertaken directly with the phenomenological model it was relatively straightforward to achieve good control performance. Nevertheless, control degraded sharply when the output of the phenomenological model was contaminated with noise using our realistic noise model, even with proper signal filtering.
Assuntos
Reatores Biológicos/microbiologia , Técnicas de Cultura de Células/instrumentação , Gibberella/metabolismo , Giberelinas/metabolismo , Modelos Biológicos , Triticum/microbiologia , Artefatos , Técnicas de Cultura de Células/métodos , Simulação por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Retroalimentação/fisiologia , Fermentação/fisiologia , Processos EstocásticosRESUMO
Use of visual information in interceptive actions requiring large-scale changes to movement timing was investigated. The task consisted of intercepting a moving target on a monitor screen through an angular arm movement. In half of the trials, the initial target velocity of 8 cm/s was unexpectedly decreased to 4 cm/s or increased to 12 cm/s, leaving 800 ms to target arrival after velocity change. Visual information about target displacement was manipulated by interpolating full vision with occlusion of the last 200, 400, or 600 ms before the due time of interception. The results revealed that reduction of visual exposure of target displacement affected movement variability, but not arm velocity or directional trend of temporal errors. This finding supports the concept that motor control in interception is based on an internal representation of target displacement, formed during the initial portion of visual exposure following velocity change, which is updated by further visual information of target displacement.
Assuntos
Retroalimentação/fisiologia , Movimento/fisiologia , Desempenho Psicomotor/fisiologia , Percepção Espacial/fisiologia , Percepção Visual/fisiologia , Adulto , Braço/inervação , Braço/fisiologia , Feminino , Humanos , Masculino , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Testes Neuropsicológicos , Orientação/fisiologia , Estimulação Luminosa , Tempo de Reação/fisiologia , Fatores de TempoRESUMO
Modular approaches are powerful systems biology strategies to deal with complexity. They consist in lumping conceptually all that is irrelevant to the problem under study, leaving explicit the portions of interest. Modular (or top-down) metabolic control analysis is a theoretical and experimental approach to study the sensitivity properties of complex metabolic systems. Initially, it was conceived for infinitesimal changes but, recently, it started to be developed for large metabolic changes. A central result of this approach is that the systemic properties, represented by control coefficients, can be expressed as a function of the properties of isolated modules, the elasticity coefficients. Here we extend the theory for large changes to the case that the elasticity coefficients depend on the extent of the change. The novel theory is used to analyse experimental data related to the control of glycolytic flux in Escherichia coli. Our analysis shows that the pattern of control for large changes is quantitatively and qualitatively different from the one obtained applying the infinitesimal treatment.
Assuntos
Algoritmos , Fenômenos Fisiológicos Celulares , Metabolismo/fisiologia , Modelos Biológicos , Proteoma/metabolismo , Transdução de Sinais/fisiologia , Simulação por Computador , Elasticidade , Retroalimentação/fisiologia , Cinética , Sensibilidade e EspecificidadeRESUMO
Dynamic models of molecular networks and pathways enable in silico evaluations of the consistency of proposed interactions and the outcomes of perturbations as well as of hypotheses on system-level structure and function. We postulate a continuous model of the activation dynamics of the ethylene response factor 1 (ERF1) gene in response to ethylene signaling. This activation elicits the response of the plant defensin 1 (PDF1) gene, which also responds to jasmonic acid, and the inhibition of the putative auxin responsive factor 2 (ARF2) gene, that also responds to auxin. Our model allows the effect of different ethylene concentrations in eliciting contrasting genetic and phenotypic responses to be evaluated allows the effect of different ethylene concentrations in eliciting contrasting genetic and phenotypic responses to be evaluated and seems to consider key components of the ethylene pathway because the ERF1 dose-response curve that we predict has the same qualitative form as the phenotypic dose-response curves obtained experimentally. Therefore, our model suggests that the phenotypic dose-response curves obtained experimentally could be due, at least in part, to ERF1 changes to different ethylene concentrations. Stability analyses show that the model's results are robust to parameter estimates. Of interest is that our model predicts that the ethylene pathway may filter stochastic and rapid chaotic fluctuations in ethylene availability. This novel approach may be applied to any cellular signaling and response pathway in plants and animals.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas de Ligação a DNA/metabolismo , Etilenos/metabolismo , Modelos Biológicos , Proteínas de Plantas/metabolismo , Proteínas Repressoras/metabolismo , Transdução de Sinais/fisiologia , Simulação por Computador , Retroalimentação/fisiologia , Regulação da Expressão Gênica de Plantas/fisiologia , Modelos Estatísticos , Processos EstocásticosRESUMO
In this study we investigated the hypothesis that the simple set of rules used to explain the modulation of muscle activities during single-joint movements could also be applied for reversal movements of the shoulder and elbow joints. The muscle torques of both joints were characterized by a triphasic impulse. The first impulse of each joint accelerated the limb to the target and was generated by an initial burst of the muscles activated first (primary mover). The second impulse decelerated the limb to the target, reversed movement direction and accelerated the limb back to the initial position, and was generated by an initial burst of the muscles activated second (secondary movers). A third impulse, in each joint, decelerated the limb to the initial position due to the generation of a second burst of the primary movers. The first burst of the primary mover decreased abruptly, and the latency between the activation of the primary and secondary movers varied in proportion with target distances for the elbow, but not for the shoulder muscles. All impulses and bursts increased with target distances and were well coupled. Therefore, as predicted, the bursts of muscle activities were modulated to generate the appropriate level of muscle torque.
Assuntos
Braço/fisiologia , Atividade Motora/fisiologia , Movimento/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Equilíbrio Postural/fisiologia , Adaptação Fisiológica/fisiologia , Adolescente , Adulto , Retroalimentação/fisiologia , Feminino , Humanos , Masculino , TorqueRESUMO
The Hindmarsh-Rose (HR) system of equations is a model that captures the essential of the spiking activity of biological neurons. In this work we present an exploratory numerical study of the time activities of two HR neurons interacting through electrical synapses. The knowledge of this simple system is a first step towards the understanding of the cooperative behavior of large neural assemblies. Several periodic and chaotic attractors where identified, as the coupling strength is increased from zero until the perfect synchronization regime. In addition to the known phase locking synchronization at weak coupling, electrical synapses also allow for both in-phase and antiphase synchronization from moderate to strong coupling. A regime where the system changes apparently randomly between in-phase and antiphase locking evolves to a bistability regime, where both in-phase and antiphase periodic attractors are locally stable. At the strong coupling regime in-phase chaotic evolution dominates, but windows with complex periodic behavior are also present.
Assuntos
Potenciais de Ação/fisiologia , Relógios Biológicos/fisiologia , Modelos Neurológicos , Rede Nervosa/fisiologia , Neurônios/fisiologia , Periodicidade , Transmissão Sináptica/fisiologia , Algoritmos , Simulação por Computador , Retroalimentação/fisiologia , Dinâmica não LinearRESUMO
We used a particular computational approach, the uncontrolled manifold hypothesis, to investigate joint angle covariation patterns during whole-body actions performed by standing persons. We hypothesized that two kinematic synergies accounted for the leg/trunk joint covariation across cycles during a rhythmic whole-body motion to stabilize two performance variables, the trunk orientation in the external space and the horizontal position of the center of mass (COM). Subjects stood on a force plate and performed whole-body rhythmic movements for 45 s under visual feedback on one of the four variables, the position of the center of pressure or the angle in one of the three joints (ankle, knee, or hip). The Fitts-like paradigm was used with two target amplitudes and six indices of difficulty (ID) for each of the four variables. This was done to explore the robustness of kinematic postural synergies. A speed-accuracy trade-off was observed in all feedback conditions such that the movement time scaled with ID and the scaling differed between the two movement amplitudes. Principal-component (PC) analysis showed the existence of a single PC in the joint space that accounted for over 95% of the joint angle variance. Analysis within the uncontrolled manifold hypothesis has shown that data distributions in the joint angle space were compatible with stabilization of both trunk orientation and COM location. We conclude that trunk orientation and the COM location are stabilized by co-varied changes of the major joint angles during whole-body movements. Despite the strong effects of movement amplitude and ID on performance, the structure of the joint variance showed only minor dependence on these task parameters. The two kinematic synergies (co-varied changes in the joint angles that stabilized the COM location and trunk orientation) have proven to be robust over a variety of tasks.
Assuntos
Articulações/fisiologia , Modelos Biológicos , Movimento/fisiologia , Equilíbrio Postural/fisiologia , Postura/fisiologia , Desempenho Psicomotor/fisiologia , Volição/fisiologia , Adaptação Fisiológica/fisiologia , Adulto , Fenômenos Biomecânicos/métodos , Simulação por Computador , Retroalimentação/fisiologia , Feminino , Humanos , MasculinoRESUMO
Horneros (Furnarius Rufus) are South American birds well known for their oven-looking nests and their ability to sing in couples. Previous work has analyzed the rhythmic organization of the duets, unveiling a mathematical structure behind the songs. In this work we analyze in detail an extended database of duets. The rhythms of the songs are compatible with the dynamics presented by a wide class of dynamical systems: forced excitable systems. Compatible with this nonlinear rule, we build a biologically inspired model for how the neural and the anatomical elements may interact to produce the observed rhythmic patterns. This model allows us to synthesize songs presenting the acoustic and rhythmic features observed in real songs. We also make testable predictions in order to support our hypothesis.
Assuntos
Relógios Biológicos/fisiologia , Laringe/fisiologia , Modelos Neurológicos , Rede Nervosa/fisiologia , Aves Canoras/fisiologia , Espectrografia do Som/métodos , Vocalização Animal/fisiologia , Potenciais de Ação/fisiologia , Comunicação Animal , Animais , Simulação por Computador , Retroalimentação/fisiologia , Feminino , Nervos Laríngeos/fisiologia , PeriodicidadeRESUMO
We present a simple model for birdsong production in Oscine songbirds that allows us to study the acoustic interaction between their two sound sources, as well as the acoustic coupling between sources and vocal tract. This model allows us to study complex phenomena in which the traditionally assumed source-filter separation hypothesis does not hold. We make testable hypotheses about the source of complexity in the song of some birds.
Assuntos
Relógios Biológicos/fisiologia , Modelos Biológicos , Oscilometria/métodos , Fonação/fisiologia , Aves Canoras/fisiologia , Prega Vocal/fisiologia , Vocalização Animal/fisiologia , Acústica , Pressão do Ar , Animais , Simulação por Computador , Retroalimentação/fisiologia , Dinâmica não Linear , VibraçãoRESUMO
We numerically study the synchronization behavior of a coupled map lattice consisting of a chain of chaotic logistic maps exhibiting power law interactions. We report two main results. First, we find a practical lower bound in the lattice size in order that this system could be considered in the thermodynamic limit in numerical simulations. Second, we observe the existence of a strong correlation between the Lyapunov dimension and the averaged synchronization time.