Добірка наукової літератури з теми "Inferior colliculus Computer simulation"

Saccadic accuracy requires that the control signal sent to the motor neurons must be the right size to bring the fovea to the target, whatever the initial position of the eyes (and corresponding state of the eye muscles). Clinical and experimental evidence indicates that the basic machinery for generating saccadic eye movements, located in the brainstem, is not accurate: learning to make accurate saccades requires cerebellar circuitry located in the posterior vermis and fastigial nucleus. How do these two circuits interact to achieve adaptive control of saccades? A model of this interaction is described, based on Kawato's principle of feedback-error-learning. Its three components were (1) a simple controller with no knowledge of initial eye position, corresponding to the superior colliculus; (2) Robinson's internal feedback model of the saccadic burst generator, corresponding to preoculomotor areas in the brain-stem; and (3) Albus's Cerebellar Model Arithmetic Computer (CMK), a neural net model of the cerebellum. The connections between these components were (I) the simple feedback controller passed a (usually inaccurate) command to the pulse generator, and (2) a copy of this command to the CMAC; (3) the CMAC combined the copy with information about initial eye position to (4) alter the gain on the pulse generator's internal feedback loop, thereby adjusting the size of burst sent to the motor neurons. (5) If the saccade were inaccurate, an error signal from the feedback controller adjusted the weights in the CMAC. It was proposed that connection (2) corresponds to the mossy fiber projection from superior colliculus to oculomotor vermis via the nucleus reticularis tegmenti pontis, and connection (5) to the climbing fiber projection from superior colliculus to the oculomotor vermis via the inferior olive. Plausible initialization values were chosen so that the system produced hypometric saccades (as do human infants) at the start of learning, and position-dependent hypermetric saccades when the cerebellum was removed. Simulations for horizontal eye movements showed that accurate saccades from any starting position could be learned rapidly, even if the error signal conveyed only whether the initial saccade were too large or too small. In subsequent tests the model adapted realistically both to simulated weakening of the eye muscles, and to intrasaccadic displacement of the target, thereby mimicking saccadic plasticity in adults. The architecture of the model may therefore offer a functional explanation of hitherto mysterious tectocerebellar projections, and a framework for investigating in greater detail how the cerebellum adaptively controls saccadic accuracy.

Aging is associated with functional and morphological changes in the sensory organs, including the auditory system. Mitophagy, a process that regulates the turnover of dysfunctional mitochondria, is impaired with aging. This study aimed to investigate the effect of aging on mitophagy in the central auditory system using an age-related hearing loss mouse model. C57BL/6J mice were divided into the following four groups based on age: 1-, 6-, 12-, and 18-month groups. The hearing ability was evaluated by measuring the auditory brainstem response (ABR) thresholds. The mitochondrial DNA damage level and the expression of mitophagy-related genes, and proteins were investigated by real-time polymerase chain reaction and Western blot analyses. The colocalization of mitophagosomes and lysosomes in the mouse auditory cortex and inferior colliculus was analyzed by immunofluorescence analysis. The expression of genes involved in mitophagy, such as PINK1, Parkin, and BNIP3 in the mouse auditory cortex and inferior colliculus, was investigated by immunohistochemical staining. The ABR threshold increased with aging. In addition to the mitochondrial DNA integrity, the mRNA levels of PINK1, Parkin, NIX, and BNIP3, as well as the protein levels of PINK1, Parkin, BNIP3, COX4, LC3B, mitochondrial oxidative phosphorylation (OXPHOS) subunits I–IV in the mouse auditory cortex significantly decreased with aging. The immunofluorescence analysis revealed that the colocalization of mitophagosomes and lysosomes in the mouse auditory cortex and inferior colliculus decreased with aging. The immunohistochemical analysis revealed that the expression of PINK1, Parkin, and BNIP3 decreased in the mouse auditory cortex and inferior colliculus with aging. These findings indicate that aging-associated impaired mitophagy may contribute to the cellular changes observed in an aged central auditory system, which result in age-related hearing loss. Thus, the induction of mitophagy can be a potential therapeutic strategy for age-related hearing loss.

The human auditory system has an exceptional ability to separate competing sounds, but the neural mechanisms that underlie this ability are not understood. Responses of inferior colliculus (IC) neurons to “mistuned” complex tones were measured to investigate possible neural mechanisms for spectral segregation. A mistuned tone is a harmonic complex tone in which the frequency of one component has been changed; that component may be heard as a separate sound source, suggesting that the mistuned tone engages the same mechanisms that contribute to the segregation of natural sounds. In this study, the harmonic tone consisted of eight harmonics of 250 Hz; in the mistuned tone, the frequency of the fourth harmonic was increased by 12% (120 Hz). The mistuned tone elicited a stereotypical discharge pattern, consisting of peaks separated by about 8 ms and a response envelope modulated with a period of 100 ms, which bore little resemblance to the discharge pattern elicited by the harmonic tone or to the stimulus waveform. Similar discharge patterns were elicited from many neurons with a range of characteristic frequencies, especially from neurons that exhibited short-latency sustained responses to pure tones. In contrast, transient and long-latency neurons usually did not exhibit the stereotypical discharge pattern. The discharge pattern was generally stable when the stimulus level or component phase was varied; the major effect of these manipulations was to shift the phase of the response envelope. Simulation of IC responses with a computational model suggested that off-frequency inhibition could produce discharge patterns with these characteristics.

The precedence effect (PE) is an auditory phenomenon involved in suppressing the perception of echoes in reverberant environments, and is thought to facilitate accurate localization of sound sources. We investigated physiological correlates of the PE in the inferior colliculus (IC) of anesthetized cats, with a focus on directional mechanisms for this phenomenon. We used a virtual space (VS) technique, where two clicks (a “lead” and a “lag”) separated by a brief time delay were each filtered through head-related transfer functions (HRTFs). For nearly all neurons, the response to the lag was suppressed for short delays and recovered at long delays. In general, both the time course and the directional patterns of suppression resembled those reported in free-field studies in many respects, suggesting that our VS simulation contained the essential cues for studying PE phenomena. The relationship between the directionality of the response to the lead and that of its suppressive effect on the lag varied a great deal among IC neurons. For a majority of units, both excitation produced by the lead and suppression of the lag response were highly directional, and the two were similar to one another. For these neurons, the long-lasting inhibitory inputs thought to be responsible for suppression seem to have similar spatial tuning as the inputs that determine the excitatory response to the lead. Further, the behavior of these neurons is consistent with psychophysical observations that the PE is strongest when the lead and the lag originate from neighboring spatial locations. For other neurons, either there was no obvious relationship between the directionality of the excitatory lead response and the directionality of suppression, or the suppression was highly directional whereas the excitation was not, or vice versa. For these neurons, the excitation and the suppression produced by the lead seem to depend on different mechanisms. Manipulation of the directional cues (such as interaural time and level differences) contained in the lead revealed further dissociations between excitation and suppression. Specifically, for about one-third of the neurons, suppression depended on different directional cues than did the response to the lead, even though the directionality of suppression was similar to that of the lead response when all cues were present. This finding suggests that the inhibitory inputs causing suppression may originate in part from subcollicular auditory nuclei processing different directional cues than the inputs that determine the excitatory response to the lead. Neurons showing such dissociations may play an important role in the PE when the lead and the lag originate from very different directions.

Using an animal model, we have studied the response of the auditory brain stem to cochlear implantation and the effect of intracochlear factors on this response. Neonatally, pharmacologically deafened cats (100 to more than 180 days old) were implanted with a 4-electrode array in both cochleas. Then, the left cochlea of each cat was electrically stimulated for total periods of up to 1000 hours. After a terminal 14C-2-deoxyglucose (2DG) experiment, the fraction of the right inferior colliculus with a significant accumulation of 2DG label was calculated. Using 3-dimensional computer-aided reconstruction, we examined the cochleas of these animals for spiral ganglion cell (SGC) survival and intracochlear factors such as electrode positions, degeneration of the organ of Corti, and the degree of fibrosis of the scala tympani. The distribution of each parameter was calculated along the organ of Corti from the basal end. There was a positive correlation between SGC survival and the level of fibrosis in the scala tympani, and a negative correlation between SGC survival and the degree of organ of Corti degeneration. Finally, there was a negative correlation between the 2DG-labeled inferior colliculus volume fraction and the degree of fibrosis, particularly in the 1-mm region nearest the pair of electrodes, and presumably in the basal turn.

Estimativa das forças musculares de diabéticos pode apoiar a compreensão das estratégias mecânicas e musculares que esses pacientes adotam para preservar a habilidade de realizar a marcha e garantir sua independência à medida que lidam com seus déficits neurais e musculares devido a diabetes e à neuropatia. O objetivo do presente estudo foi estimar a distribuição da força muscular do membro inferior durante a marcha em pacientes diabéticos com e sem neuropatia diabética, bem como compará-los com indivíduos saudáveis. Dados de força de reação do solo (100 Hz) e cinemática tridimensional do tornozelo, joelho e quadril (100 Hz) de 10 diabéticos neuropatas (GDN), 10 diabéticos não neuropatas (GD) e 10 indivíduos saudáveis (GC) foram utilizados como variáveis de entrada para o modelo musculoesquelético computacional gait 2392 (23 graus de liberdade e 92 atuadores musculoesqueléticos) no software OpenSim. O modelo genérico padrão foi dimensionado para se adequar à antropometria de cada indivíduo coletado, antes da execução das simulações. O modelo musculoesquelético dos indivíduos diabéticos neuropatas apresentou força isométrica máxima reduzida em 30% para os extensores do tornozelo e 20% para os dorsiflexores do tornozelo, buscando aproximar o modelo da redução de força muscular distal consequente à neuropatia diabética exibida por pacientes. As séries temporais da força dos músculos dos membros inferiores foram calculadas usando o procedimento de otimização estática. As forças musculares máximas foram calculadas durante intervalos do ciclo de marcha em que a ação dos músculos é fundamental para execução da tarefa. Os picos de força foram comparados entre os grupos de indivíduos utilizando MANOVA para os grupos musculares flexores e extensores das articulações do quadril, joelho e tornozelo, seguidas de ANOVA e pós-hoc de Newman-Keuls (p < 0,05). GDN apresentou maior pico de força dos músculos flexores de joelho (bíceps femoral cabeça curta/ p < 0,001, semitendinoso/ p < 0,001 e semimenbranoso/ p < 0,001) na fase de propulsão, em relação à GD e GC. GDN também apresentou menor pico de força dos músculos gastrocnêmio medial e sóleo, bem como maior pico de força para gastrocnêmio lateral comparado a GD e GC, nesta mesma fase. GD exibiu menor pico de força dos músculos extensores de quadril (semitendinoso e semimembranoso) ao final da fase de balanço e músculos abdutores do quadril durante a fase de apoio, bem como maior pico de força para os músculos extensores de joelho (vasto medial e lateral/ p = 0,004) no início da fase de apoio, comparado a GDN e GC. Os pacientes diabéticos com e sem neuropatia adotam distintas estratégias de distribuição de força muscular, apesar da piora progressiva em seu estado de saúde. Ambos os grupos diabéticos demonstraram alterações na produção de força dos músculos extensores de tornozelo, com redução do pico de força do sóleo (GD) e gastrocnêmio medial (GDN), entretanto, apenas o GDN aumentou o pico de força dos isquiotibiais (flexores de joelho) na fase de propulsão. GD apresentou redução expressiva da produção de força do glúteo médio, o que pode sugerir prejuízo para a estabilização látero-lateral da pelve. Pode-se considerar incluir programas de treinamento de resistência de músculos proximais relacionados à articulação do joelho em uma rotina de reabilitação para pacientes diabéticos. Outras inclusões potenciais em protocolos de reabilitação são o treino de marcha e a prática de exercícios funcionais com foco na ativação dos músculos isquiotibiais
Muscle force estimation could support a better understanding of the mechanical and muscular strategies that diabetic patients adopt to preserve walking ability and to guarantee their independence as they deal with their neural and muscular impairments due to diabetes and neuropathy. Our aim was to estimate and compare the lower limb\'s muscle force distribution during gait in diabetic patients with and without diabetic neuropathy. Data from ground reaction force (AMTI OR61000 force plate at 100Hz) and three-dimensional kinematics of ankle, knee and hip (eight-camera Optitrack® at 100 Hz) of 10 neuropathic (DNG), 10 diabetic non-neuropathic (DG) and 10 healthy individuals (CG) were used as input variables for the musculoskeletal model gait 2392 (23 degrees of freedom and 92 musculoskeletal actuators) in the OpenSim software. The standard generic model was scaled to fit the anthropometry of each individual collected, prior to the execution of the simulations. The musculoskeletal model of neuropathic individuals presented maximum isometric force reduced in 30% for ankle extensors and 20% for ankle dorsiflexors to mimic the atrophy of ankle muscles due to diabetic neuropathy. The force time series of lower limb muscles were calculated using the static optimization procedure. The peak muscle forces were calculated during selected time bands of the gait cycle. The peak force was compared between groups using MANOVA for the flexor and extensor muscle groups of hip, knee and ankle joints followed by ANOVA and post-hoc of Newman-Keuls (p < 0.05). DNG showed higher knee flexors peak force (biceps femoris short head / p < 0,001, semitendinous / p < 0,001 and semimenbranous / p < 0,001) during push-off, compared to DG and CG. DNG also presented lower peak force for gastrocnemius medialis and soleus, as well as higher peak force for gastrocnemius lateralis compared to DG and CG in the same gait phase. DG exhibited lower peak force for the hip extensor muscles (semitendinous and semimembranous) in the final swing and hip abductor muscles during stance, as well as higher peak force for the knee extensor muscles (vastus medialis and lateralis / p=0,004) in the early stance compared to DNG and CG. Diabetic patients with and without neuropathy appear to adopt different muscle force distribution strategies in spite of the progressive worsening in their health condition. While reducing ankle extensor forces, DG increased knee extensor muscle forces at early stance and reduced the hamstrings force at the end of swing phase, whereas DNG increased the hamstrings muscle forces at push-off. A resistance training program for the proximal muscles related to the knee joint could be considered in a rehabilitation routine for diabetic patients. Other potential inclusions in rehabilitation protocols consist of gait retraining and practicing functional exercises focusing on the activation of the hamstring muscles

Discusses the rise of information technology functions in higher education and the related advent of quality standards for on-line education. The limited nature of existing guidelines is emphasized, particularly in the dimension of establishing authentic relationships, empowerment of faculty and students, and the inculcation of critical thinking. The Borkian vision of the future of education is summarized and contrasted with the limits if not failure of the legacies of past large-scale educational investments in programmed learning and in computer simulation. The drift toward mandated standards in on-line/distance education is discussed as well as the tension of this with empowerment concepts. Further contrast is drawn between the competing models of the university as “community of scholars” and as “marketplace of consumers.” Cost-cutting motives for on-line course delivery are explored in some detail, raising issues about radical proposals to restructure university teaching functions. A hybrid model, involving both computer-mediated and face-to-face methods, is seen as the superior instructional strategy, but the cost of this model raises the danger that a two-tier educational system will emerge – a more expensive upper tier with sound traditional education supplemented with the benefits of electronic media, and a cheaper, inferior tier dispensing programmed training to meet objectives far narrower than the traditional goals of liberal education.

Advancements in technology have led to the ability to tag virtually any cell with magnetic particles so long as the surface protein is known. In theory, these tagged cells may then be identified, imaged, or manipulated by magnetic force. In vitro separation using a magnetized stent and magnetically tagged cells was demonstrated by [1]. The motivation for this work was to investigate the feasibility of a magnetized inferior vena cava (IVC) filter for in vivo separation of metastatic cancer cells from the bloodstream. In use, the device would consist of a standard IVC filter plated with nickel, making it paramagnetic yet still biocompatible. The IVC filter is placed inside the vena cava, as is routinely done for other applications. Permanent magnets, which the patient would wear as an external vest, generate a field and the presence of the magnetized filter within this field can attract magnetic particles to the filter. In particular, our goal was to develop a numerical model that could be used to assess the feasibility and performance of such a device over a range of design space.

The demand for total knee arthroplasty (TKA) is increasing steadily. In 2007, Kurtz et al. [1] predicted that TKA procedures would increase from 402,100 in 2003 to 3.48 million by 2030. Recent US national inpatient survey data have borne out these trends [2, 3]. Furthermore, demand is growing fastest in people younger than 65 [4] — patients who will need their implants to last the longest. The major factors limiting prosthesis longevity involve wear of the polyethylene bearing surfaces. Wear continues to be a problem at the knee; for example, advances that reduce hip implant wear such as crosslinking of polyethylene are not widely used in TKA due to fears of early material breakdown under knee loading conditions [5]. Preclinical TKA testing is performed with knee wear simulators under generic walking conditions. Efforts are ongoing by us [6] and others [7] to improve the physiological relevance of current testing standards. Nevertheless, a simulator would need to run ∼eight months continuously to simulate 20 years of walking, assuming one-million steps per year and speed of one cycle per second. As a complementary tool, computational models can test multiple conditions efficiently and ensure a faster turnaround time in the design process to eliminate inferior designs earlier. The purpose of this work is to describe a computational framework for predicting TKA loading, and ultimately implant longevity, on a patient-specific basis. The rationale is that, after developing a patient-specific computational framework, TKA designs of any material and under any patient behavior can be modulated to promote contact conditions best for implant longevity.

This paper presents practical experience in constructing stereo presentations of texts and formulas on an autostereoscopic monitor in stereo presentations designed to display the results of numerical simulation. The task of constructing stereo images of texts and formulas is a structural subtask of a general study devoted to the development of methods and algorithms for constructing stereo presentations of the results of scientific research. This paper discusses the construction of stereoscopic images on an autostereoscopic monitor. The autostereoscopic monitor allows one to observe a stereo image without glasses, while ensuring the quality of the stereo image, which is not inferior to the quality of the stereo image, presented using a classic 3D projection stereo system. Various methods of obtaining stereo images supported by the monitor were tested, namely, the multi-view presentation of the object and the construction of depth maps. The results for both methods are presented.