Os interneurônios do bulbo olfatório são elementos chave para o entendimento do processamento de odores. O papel funcional desses neurônios ainda não é bem compreendido, em especial o papel da célula periglomerular (PG). O presente trabalho consiste em construir um modelo biologicamente plausível da célula PG e investigar os efeitos dessa célula em conjunto com modelos da célula mitral e da célula granular. Esses modelos são acoplados através de conexões sinápticas inspiradas nas conexões existentes no bulbo olfatório, formando uma pequena rede simplificada. A rede é usada para analisar o efeito da inibição inicial da célula mitral por parte da célula PG e os mecanismos que podem influenciar o padrão de atividade da célula mitral. Através deste estudo, verifica-se que a célula PG pode influenciar na frequência, no tempo de disparo e gerar atrasos na propagação do potencial da célula mitral, agindo como um mecanismo de controle nas camadas iniciais do processamento de odores do bulbo olfatório. / Interneurons of the olfactory bulb are key elements for understanding odor processing. The functional role of these cells are not yet well understood, in particular the role of periglomerular cell (PG). This work aims at constructing a biologically plausible model of the PG cell to study effects of the coupling of this cell with model of mitral and granule cells of the olfactory bulb. Single cell models of these three cell types coupled by synaptic connections inspired on existing connections in the olfactory bulb, constituting a small and simple network. This network is used to investigate the effect of early lateral inhibition of the mitral cell by PG cell and the mechanisms witch can influence the output activity pattern of mitral cell. The study shows that the PG cell may influence the spike frequency and the spike timing of the mitral cell, as well as provoke delays in the propagation of action potential along this cell. Therefore, the PG cell may act as a control mechanism in the early odor processing stages in the olfactory bulb.

Satellite-framed languages and verb-framed languages differ in how they encode motion events. English encodes or lexicalizes Path in verb particles, prepositional phrases, or satellites associated with the main verb. In contrast, Turkish tends to encode Path in the main verb of a clause. When describing motion events, English speakers typically use verbs that convey information about manner rather than path, whereas Turkish speakers do the opposite. In this study, we investigated whether this crosslinguistic difference between English and Turkish influences how the speakers of these languages perform in a non-linguistic recognition memory task. In a video description task, English speakers used more manner verbs in the main verb of sentences than Turkish speakers did. In the recognition memory task, English speakers attended more strongly than Turkish speakers did to path of motion. English and Turkish speakers attended equally to manner of motion, however, providing no support for the linguistic relativity hypothesis. / by Ferhat Karaman. / Thesis (M.A.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

We sought to better understand human motor control by investigating functional interactions between the Supplementary Motor Area (SMA), dorsal Anterior Cingulate Cortex (dACC), and primary motor cortex (M1) in healthy adolescent participants performing visually coordinated unimanual finger-movement and n-back working memory tasks. We discovered modulation of the SMA by the dACC by analysis of fMRI BOLD time series recorded from the three ROIs (SMA, dACC, and M1) in each participant. Two measures of functional interaction were used: undirected functional connectivity was measured using the Pearson product-moment correlation coefficient (PMCC), and directed functional connectivity was measured from linear autoregressive (AR) models. In the first project, task-specific modulation of the SMA by the dACC was discovered while subjects performed a coordinated unimanual finger-movement task, in which the finger movement was synchronized with an exogenous visual stimulus. In the second project, modulation of the SMA by the dACC was found to be significantly greater in the finger coordination task than in an n-back working memory, in which the same finger movement signified a motor response indicating a 0-back or 2-back working memory match. We thus demonstrated in the first study that the dACC sends task-specific directed signals to the supplementary motor area, suggesting a role for the dACC in top-down motor control. Finally, the second study revealed that these signals were significantly greater in the coordinated motor task than in the n-back working memory task, suggesting that the modulation of the SMA by the dACC was associated with sustained, continuous motor production and/or motor expectation, rather than with the motor movement itself. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

A precisão de uma ação motora depende de vários fatores, como: 1) grau de variabilidade da força gerada por cada músculo envolvido, 2) velocidade de geração da força, 3) coordenação das ativações dos músculos. A geração e o controle da força muscular possuem mecanismos que ainda precisam ser mais bem estabelecidos, tanto para o aprimoramento das teorias de controle motor, quanto para o desenvolvimento de técnicas que permitam a prevenção ou a compensação de certas deficiências. A perda de desempenho motor pode ser decorrente de doenças que afetam o sistema neuromuscular ou de alterações associadas ao envelhecimento. Sabe-se, por exemplo, que idosos podem possuir maior variabilidade e menor velocidade de desenvolvimento da força, quando comparados com jovens. Uma das formas de se entender os mecanismos responsáveis pelos fenômenos observados em experimentos neurofisiológicos, em indivíduos saudáveis, em pacientes ou em idosos, é por meio de uma representação adequada de tais mecanismos em modelos matemáticos. Tais modelos podem, pela escolha de um conjunto de parâmetros e de sinais de entrada, ser simulados, explorando-se toda gama de cenários plausíveis para a geração de um determinado fenômeno, tendo como referência os dados obtidos experimentalmente. Resumidamente, o presente trabalho trata do estudo do sistema neuromuscular por modelagem matemática e simulação computacional, com particular interesse nos músculos do tríceps sural e no primeiro interósseo dorsal (um músculo intrínseco da mão), sendo estes músculos amplamente utilizados em estudos experimentais e de modelagem. Maior enfoque é dado em contrações isométricas (i.e., ângulo articular mantido fixo), avaliando-se a organização do núcleo motor, em termos anatômicos e fisiológicos, recebendo como entrada a atividade sináptica das vias pré-motoneuronais, e estudando como diferentes arranjos das propriedades neurais podem resultar em características encontradas experimentalmente para a força muscular. Inicialmente foi feita uma ampla expansão de um simulador existente (ReMoto), tanto em aspectos de modelagem quanto de interface. Em seguida, este modelo expandido foi empregado para um estudo da influência do grau de rigidez muscular nas respostas reflexas do tornozelo. Posteriormente, um novo modelo de pool de motoneurônios, com ampla representação de características biofísicas, foi desenvolvido e, por fim, este modelo foi utilizado, em conjunto com modelos de tratos descendentes e da geração de força muscular, para representar a geração de forças isométricas em jovens e idosos. / The precision of a motor action depends on several factors such as: 1) the level of force variability of each involved muscle, 2) the rate of force development, 3) the coordination of the activations of the muscles involved. Several mechanisms underlying the force generation in a muscle and its control by the nervous system remain to be fully comprehended. An appropriate description of these mechanisms would allow an improvement in motor control theories and could contribute to the development of techniques for the prevention or compensation of some disabilities. Losses in motor performance may be caused by diseases affecting the neuromuscular system or due to aging processes. For instance, old adults may exhibit higher force variability and lower velocity of force development than young adults. Proper representations of such mechanisms in mathematical models constitute a promising way to test hypotheses raised by neurophysiological experiments to explain an observed phenomenon. These models can be used to investigate aspects of health/disease or young/old subjects and, by varying their parameter sets, it is possible to explore a broad range of plausible scenarios under which the experimentally observed phenomena are replicated. This project deals with the study of the neuromuscular system by mathematical modeling and computer simulations, applied to the triceps surae and the first dorsal interosseus (two of the most experimentally and theoretically studied muscles). The principal focus is on isometric contractions (i.e., fixed joint angle) and the study of the organization of the motor nucleus (anatomical and physiological aspects) receiving inputs from premotoneuronal pathways. The study analyzes how different patterns of organization result in experimentally observed aspects of muscle force. Initially, an existing simulator of the neuromuscular system (ReMoto) was broadly extended to include new models and a friendly interface. The extended model was used to investigate the influence of muscle stiffness on the reflex responses in the ankle joint. Next, a new motoneuron pool mathematical model was developed based on known biophysics. Finally, this model was integrated with models of pre-motoneuronal neurons estabilishing synapses with motoneurons and of muscle force generation in order to represent isometric force generation in young and old adults.

Desde as descobertas das propriedades dos campos receptivos dos neurônios corticais no córtex visual primário, sua organização tem sido estudada com o auxílio de diversos métodos como eletrofisiologia, imageamento cortical e neurociência computacional. Poucos modelos mostram-se capazes de apresentar dominância ocular e seletividade à orientação simultaneamente. Um modelo em larga escala do sistema visual primário de mamíferos foi construído usando o GENESIS 2.2. O modelo contém aproximadamente 10.000 neurônios biologicamente plausíveis em oito matrizes representando setores das duas retinas, duas lâminas do núcleo geniculado lateral dorsal e duas lâminas representando o córtex visual (cada lâmina composta por uma matriz de células excitatórias e uma matriz de células inibitórias). As propriedades fisiológicas e estruturais do modelo foram determinadas com base em dados experimentais do sistema visual primário de mamíferos. Os neurônios apresentaram respostas binoculares e seletividade à orientação em boa concordância com os resultados experimentais. Apesar de neurônios corticais terem mostrado grande heterogeneidade em seus níveis de seletividade, a latência da resposta manteve-se constante e em boa concordância com resultados experimentais. / Since the discovery of the receptive field properties of cortical neurons in the primary visual cortex, their organization has been studied with many methods ranging from electrophysiology and optical imaging to computational neuroscience. Few models have been capable of showing ocularity and orientation selectivity simultaneously. A large-scale computational model of the mammalian primary visual pathway was constructed using GENESIS 2.2. The model consists of ~10,000 biologically plausible neurons organized in eight arrays to represent sectors of two retinas, two laminae of the dorsal lateral geniculate nucleus and two laminae of the visual cortex (each cortical lamina composed of a matrix of excitatory neurons and a matrix of inhibitory neurons). The physiological and architecture properties of the model were derived from experimental data for the mammalian primary visual pathway. Neurons have shown ocular and orientation selectivity dependent responses in good agreement with data. Though neurons in the cortex have shown markedly heterogeneity in the tuning responses, the latency of response was uniform and in good agreement with reported data.

O entendimento de como a informação é representada e processada no cérebro e quais são os mecanismos necessários para que isto seja possível é um dos grandes desafios da neurociência. A atividade populacional das células corticais possui dinâmica emergente bastante complexa, apresentando padrões auto-sustentados mesmo na ausência de estímulos externos. Esses padrões de atividade podem representar estados internos de auto-organização da rede neural cortical. Porém, quais características da rede cortical seriam essenciais para o entendimento deste tipo de atividade? Podemos elencar duas características fundamentais: a organização topológica da rede e as características dinâmicas das unidades funcionais da rede (os neurônios). Neste trabalho estudamos a influência da topologia e da dinâmica dos neurônios sobre a atividade auto-sustentada de dois modelos corticais diferentes. O primeiro modelo possui arquitetura hierárquica e modular construída segundo uma estratégia top-down. As simulações com este modelo mostram que criação hierárquica de módulos favorece a atividade auto-sustentada em concordância com trabalhos anteriores de outros autores. Também observamos que diferentes classes funcionais de neurônios influenciam de maneiras distintas a atividade auto-sustentada da rede. O segundo modelo possui arquitetura em camadas com regras intra- e inter-laminares específicas baseadas em dados anatômicos do córtex visual primário de gatos. As simulações com este modelo mostram um importante papel das condutâncias sinápticas excitatórias e inibitórias sobre o início da atividade auto-sustentada na rede, especialmente sobre a largura (intervalo de valores da condutância excitatória) da zona de transição entre as regiões com e sem atividade auto-sustentada no diagrama de condutâncias sinápticas. Conclui-se que a topologia da rede cortical e sua composição em termos de combinações de neurônios de diferentes tipos têm importante papel sobre a existência e as propriedades da atividade auto-sustentada na rede. / To understand how information is represented and processed in the brain and the necessary mechanisms for this is one of the major challenges in neuroscience. The population activity of cortical cells has complex and emergent dynamics, showing self-sustained activity patterns even in the absence of external stimuli. These activity patterns may represent internal self-organizing states of the cortical network. Which characteristics that make up the cortical network would be essential to understand this type of activity? We can list two basic characteristics: the topological organization of the network and the dynamic characteristics of its functional units (the neurons). In this work we studied the influence of topology and neuronal dynamics on self-sustained activity in two different cortical network models. The first model has hierarchical and modular architecture constructed according to a top-down strategy. Simulations with this model show that the hierarchical creation of modules favors self-sustained activity in agreement with results from other authors. We also observed that different functional neuronal classes influence in distict ways the self-sustained activity. The second model has a layered architecture with specific intra- and inter-laminar rules based on anatomical evidence from the primary visual cortex of cats. Simulations with this model show an important role of excitatory and inhibitory synaptic conductances on the beginning of self-sustained network activity, specially on the width of the border (range of excitatory conductance values) between regions with and without self-sustained activity in the excitatory-inhibitory synaptic conductances diagram. We conclude that network topology and its composition in terms of combinations of neurons with different dynamics have an important role on the existence and properties of self-sustained activity in the network.

Esse trabalho consiste no estudo de alguns mecanismos responsáveis pela geração das oscilações elétricas observadas no sistema olfativo de vertebrados e das possíveis funções que essas oscilações possam ter no processamento da informação olfativa. Da-se especial atenção ao papel desempenhado pelo ritmo respiratório e pelas sinapses químicas e elétricas nesse processo. Para realizar essa investigação, foram utilizados modelos computacionais que reproduzem aspectos da anatomia e da fisiologia do epitélio olfativo, do bulbo olfativo e do córtex piriforme. Os modelos foram desenvolvidos e simulados no neurossimulador GENESIS, funcionando no sistema operacional LINUX. A análise dos resultados foi feita no programa MATLAB (Mathworks™). Inicialmente, a tese faz uma descrição do substrato neurobiológico que compõe as camadas iniciais do sistema olfativo, incluindo o epitélio, bulbo e córtex olfativo, e de como a informação olfativa é processada por cada camada, discutindo a importância do sentido olfativo e a relevância da neurociência computacional no estudo da origem e do papel das oscilações elétricas existentes nesse sistema (Capítulo 1). O capítulo 2 descreve os materiais e métodos utilizados para a construção dos modelos computacionais e para análise dos resultados. O capítulo 3 faz uma descrição detalhada do modelo computacional utilizado e dos experimentos realizados com o modelo. Finalmente, o capítulo 4 apresenta e discute os resultados das simulações realizadas e o capítulo 5 estende essa discussão, concluindo a tese. O capítulo 6 contém as referências bibliográficas utilizadas no trabalho. Os resultados do trabalho sugerem que as oscilações elétricas no sistema olfativo poderiam ser geradas em várias estruturas e níveis de organização, abrangendo os níveis moleculares, celulares e de sistemas neurais. E que as sinapses químicas e elétricas, assim como os ritmos respiratórios, podem ter um papel fundamental na geração dessas oscilações. Assim, o modelo construído propõe uma explicação plausível para a origem das oscilações elétricas no sistema olfativo de vertebrados e discute as possíveis funções que essas oscilações teriam no contexto do processamento da informação sensorial. / This work is a study of some mechanisms associated with the generation of electric oscillations in the vertebrate olfactory system. Special attention is given for the role of the respiratory rhythm, chemical synapses and electrical synapses in this process. The possible functions of the electric oscillations in olfactory information processing are explored. A computational model that reproduces aspects of the anatomy and physiology of the olfactory epithelium, bulb and piriform cortex was utilized to realize this investigation. The models were developed and simulated in the GENESIS neurosimulator, running under the LINUX operational system. The analysis of the results was made in the software MATLAB (Mathworks™). In the beginning, the thesis describe the neurobiological substracts of the initial layers of the olfactory system, including the olfactory epithelium, bulb and piriform cortex, and explore how the olfactory information is processed by each layer. The chapter 1 presents the importance of the olfactory sense and the use of computational neuroscience to study the role of the electric oscillations in this system. The chapter 2 explains the material and methods utilized to develop the computational model and to analyse the data generated by the model. The chapter 3 describes the used computational model and the experiments realized with the model. Finally, the chapter 4 presents and discusses the results of the simulations. The chapter 5 extends the discussion and concludes the thesis. The chapter 6 contains the bibliographic references. The results of the work suggest that electric oscillations in the olfactory system could be generated in several structures and organizational levels, including the molecular level, the cellular and neural systems level. In particular, the results shown that chemical and electric synapses, as well as the respiratory rhythm, may have a fundamental role in the generation of these oscillations. Indeed, the constructed model proposes a plausible explanation for the origin of the electrical oscillations in the vertebrate olfactory system and discusses the possible function of these oscillations in the context of sensorial information processing.

Deep neural networks (DNNs) have recently been used to solve complex perceptual and decision tasks. In particular, convolutional neural networks (CNN) have been extremely successful for visual perception. In addition to performing well on the trained object recognition task, these CNNs also model brain data throughout the visual hierarchy better than previous models. However, these DNNs are still far from completely explaining visual perception in the human brain. In this thesis, we investigated two methods with the goal of improving DNNs’ capabilities to model human visual perception: (1) deep representational distance learning (RDL), a method for driving representational spaces in deep nets into alignment with other (e.g. brain) representational spaces and (2) variational DNNs that use sampling to perform approximate Bayesian inference. In the first investigation, RDL successfully transferred information from a teacher model to a student DNN. This was achieved by driving the student DNN’s representational distance matrix (RDM), which characterises the representational geometry, into alignment with that of the teacher. This led to a significant increase in test accuracy on machine learning benchmarks. In the future, we plan to use this method to simultaneously train DNNs to perform complex tasks and to predict neural data. In the second investigation, we showed that sampling during learning and inference using simple Bernoulli- and Gaussian-based noise improved a CNN’s representation of its own uncertainty for object recognition. We also found that sampling during learning and inference with Gaussian noise improved how well CNNs predict human behavioural data for image classification. While these methods alone do not fully explain human vision, they allow for training CNNs that better model several features of human visual perception.

Up to 1.2% of the population is unable to meet daily communication needs using typical speech and may use augmentative and alternative communication (AAC) strategies to communicate, including manual sign language, facial gestures, and aided strategies such as selecting targets on an onscreen keyboard. However, for individuals whose impairments affect both speech and non-speech motor systems (e.g., spinal cord injury, amyotrophic lateral sclerosis, multiple sclerosis), their ability to use manual sign and access computer systems are impacted. AAC access methods in this population remain inherently slow and effortful (e.g., eye-tracking, head-tracking, mechanical switches). Thus, optimizing communication interfaces for alternate access methods may provide significant improvements in communication rates and quality of life. In this series of studies, we developed and evaluated methods for improving communication rates through optimization and prediction in communication interfaces. These interfaces enabled participants to select sounds (phonemes) instead of letters and were computationally optimized offline via a model of human movement in order for targets likely to be selected together to be in close proximity. Online prediction was implemented such that likely targets were dynamically enlarged. Computational simulations suggested that optimized phonemic interfaces could increase communication rates by up to 30.9% compared to random phonemic interfaces. Communication rates were empirically evaluated in 36 participants without motor impairment using an alternate computer access method to produce messages with phonemic interfaces over 12 sessions. Results suggested that optimization increased communication rates by 10.5–23.0% compared to a random phonemic interface. Prediction increased communication rates during training sessions, but was not a significant factor in communication rates during the final session. Empirical evaluations in individuals with motor impairment revealed that all participants strongly agreed that they would improve with practice, and four out of six participants strongly preferred the interface with prediction. Results of these studies suggest that optimized and predictive phonemic interfaces may provide increased communication rates for individuals with motor impairments affecting both oral communication and computer access. Methods for dynamically enlarging targets may also be applicable to other (non-phonemic) interfaces to increase communication rates. Further research is needed to fully translate these results into clinical practice. / 2020-10-24T00:00:00Z

Psychotic experiences (PEs) occur in the general population, beyond psychotic disorders. PEs are a risk factor for mental ill health in young people but can occur benignly in selected samples of adults. Environmental factors predispose to PEs but their underlying mechanisms are not well-understood. Progress in understanding PEs may be limited by diverse conceptualisations, imprecise measurement and a lack of explanatory frameworks that can bridge the gaps between aetiological factors, their effects on the brain and their behavioural manifestations. In this thesis, I undertook a comprehensive investigation of the measurement, health implications, aetiology and computational mechanisms of PEs in adolescents and young adults using data from two large cohort samples, supplemented with smaller-scale behavioural studies. I first investigated the measurement of PEs. I assessed and optimised the measurement of PEs in young people by two self-report instruments. I then used latent variable modelling to show that a self-report and interview instrument measured the same underlying psychotic phenomena. Both instruments were able to measure severe PEs, while the self-report questionnaire also measured more mild psychotic phenomena. I then investigated the health implications of PEs. Using cluster analysis in both cohorts, I found replicable patterns of PEs at similar levels of intensity and persistence but with and without depressive symptoms and with varying risk of mental disorder. Paranoid ideation was more associated with depressive symptoms than non-paranoid unusual perceptions and beliefs. Childhood adversity was associated with both PE-prone groups, but later social support from family and friends was far higher in those with PEs and low depressive symptoms than those with PEs and high depressive symptoms. Subsequently, I investigated the role of the social environment in the development of PEs and psychopathology using longitudinal structural equation modelling. I found that asocial dispositions increased or preceded increase in PEs over one year, mediated by detriment to social support. Conversely, PEs did not precede or increase asociality. I then showed that dimensions of PEs and depressive symptoms were promoted by childhood adversity but differentially affected by later social support, with paranoid ideation being more influenced by support than non-paranoid unusual perceptions/beliefs. Finally, I investigated specific mechanisms of PEs in two behavioural studies. In the seventh study, I used computational modelling of reward learning to link PEs to reduced ability to modulate learning by confidence, replicating computational effects of a pharmacological model of psychosis. I also used a novel visual task to show that the manifestation of PEs as anomalous perceptions versus anomalous beliefs might be explained by over-reliance on different types of prior knowledge in perceptual inference. These results suggest that different conceptual approaches to PEs might be synthesised despite issues with their measurement. PEs in young people, while not entirely benign, are heterogeneously associated with psychopathology. Importantly, they characterise a minority of young people who are at very high transdiagnostic risk of mental illness but also occur without distress in young people, often in the context of a supportive social environment. Health outcomes in young people with PEs are predicted and potentially modified by social functioning and social relationships. PEs might arise from atypicalities in how the influences of information sources on perception and belief-updating are modulated according to their reliabilities.