Children with autism spectrum disorder (ASD) present with a myriad of diagnostic characteristics and associated behaviors. Secondarily, this population is extremely heterogeneous. Efforts have been made by many disciplines to identify more homogenous subgroups in order to improve both research and clinical outcomes. In occupational therapy, the focus has been on establishing sensory-based subtypes. This dissertation is a compilation of three separate research papers related to sensory-based subtypes in children with ASD. The first paper is a systematic review on sensory subtyping systems published in the last 12 years. Findings indicate that the majority of subtyping schemes characterize group differences by patterns of sensory responsivity (i.e., hyperresponsivity, hyporesponsivity and sensory seeking). One subtyping scheme has emerged as the most well researched of these, and includes responses to specific sensory domains for four different subtypes. The subsequent two papers presents additional research examining this subtyping system. The second paper examined neurophysiological response to sensory stimuli between the four subtypes. Salivary cortisol, skin conductance level (SCL) and respiratory sinus arrhythmia (RSA) were used examine neuroendocrine function, parasympathetic and sympathetic nervous system responses. Results indicate that parasympathetic response (as indexed by RSA) may best distinguish subtypes with typical sensory processing versus those with atypical sensory processing. More discrete differences between each of the subtypes hallmarked by different sensory processing differences were less substantial. The third paper examined functional and adaptive behaviors, in addition to clinical behaviors (psychopathology) in relationship to subtype membership. Subtypes with greater sensory processing dysfunction were found to have poorer communication, socialization and performance of daily living skills. In addition, subtypes with atypical sensory processing characteristics had higher levels of internalizing and externalizing behaviors. Again, certain subtypes were not found to differ significantly from each other on these measures. Overall findings suggest that current sensory-based subtyping schemes may not fully explain sensory processing differences or the variety of behavioral traits observed in this population. In addition, neurological reactivity patterns may not completely align with these subtype divisions. Stronger statistical differences found between certain subtypes indicates particular sensory processing characteristics may be more impairing and have more clinical relevance than others.

Investigou-se a gênese de atividade irregular em neurônios de centros geradores de padrões através de modelos eletrofisiologicamente realistas. Para tanto, foram adotadas abordagens paralelas. Primeiramente, desenvolveram-se técnicas para determinar quais os mecanismos biofísicos subjacentes aos processos de codificação de informação nestas células. Também foi proposta uma nova metodologia híbrida (baseada em continuação numérica e em varreduras força bruta) para análise de bancos de dados de modelos neuronais, permitindo estendê-los e revelar instâncias de multiestabilidade entre regimes oscilatórios e quiescentes. Além disto, a fim de determinar a origem de comportamento complexo em modelos neuronais simplificados, empregaram-se métodos geométricos da teoria de sistemas dinâmicos. A partir da análise de mapas unidimensionais perturbados por ruído, foram discutidos possíveis cenários para o surgimento de caos em sistemas dinâmicos aleatórios. Finalmente mostrou-se que, levando em conta o ruído, uma classe de modelos de condutâncias reproduz padrões de disparo observados in vivo. Estas pertubações revelam a riqueza da dinâmica transiente, levando o sistema a visitar um arcabouço determinista complexo preexistente -- sem recorrer a ajustes finos de parâmetros ou a construções ad hoc para induzir comportamento caótico. / We investigated the origin of irregularities in the dynamics of central pattern generator neurons, through analyzing electrophysiologically realistic models. A number of parallel approaches were adopted for that purpose. Initially, we studied information coding processes in these cells and proposed a technique to determine the underlying biophysical mechanisms. We also developed a novel hybrid method (based on numerical continuation and brute force sweeps) to analyze neuronal model databases, extending them and unveiling instances of multistability between oscillatory and resting regimes. Furthermore, in order to determine the origin of irregular dynamics in simplified neuronal models, we employed geometrical methods from the theory of dynamical systems. The analysis of stochastically perturbed maps allowed us to discuss possible scenarios for the generation of chaotic behaviour in random dynamical systems. Finally we showed that, by taking noise into account, a class of conductance based models gives rise to firing patterns akin to the ones observed \\emph{in vivo}. These perturbations unveil the richness of the transient dynamics, inducing the system to populate a preexistent complex deterministic scaffolding -- without resorting to parameter fine-tuning or ad hoc constructions to induce chaotic activity.

The perception of visual motion is an integral aspect of many organisms' engagement with the world. In this dissertation, a theory for the perception of visual object-motion is developed. Object-motion perception is distinguished from objectless-motion perception both experimentally and theoretically. A continuoustime dynamical neural model is developed in order to generalize the ndings and provide a theoretical framework for continued re nement of a theory for object-motion perception. Theoretical implications as well as testable predictions of the model are discussed. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Humans in the modern world can survive without the Aristotelian senses of vision, hearing, smell or taste, but no one is completely without the ability to sense touch. This sense is essential for everything from basic tasks like tool manipulation to the complex interactions that underlie social bonding, sexual reproduction and pleasure. Touch receptors are embedded in the skin, at the interface of our bodies and the world. A remarkable array of varied receptor types tile our skin to signal different features of the objects we touch and alert us to their shape and texture. An early investigator of the neurological basis of touch, Maximillian von Frey, proposed in 1895 that the morphological diversity of neural endings in the skin could represent functional specificity. It is indeed the evolution of diverse receptor structures that has endowed the sensory organ of our skin with remarkable somatosensory functions. Here I explore the evolution of mechanosensing, and discuss how diversity in form and organization of touch receptors, from the cellular to organismal level, can shape the function of touch reception.

A hallmark of intelligence in humans and other animals is the ability to engage in complex behaviors geared towards achieving far-removed goals. Such behavior relies on a set of diverse and sophisticated mental processes that are collectively referred to as cognitive or executive in nature. The prefrontal cortex (PFC) has long been considered the primary neural locus for such processes. From humans down to rodents, damage to the PFC has been shown to impair cognition and executive function. In neuropsychiatric disorders such as schizophrenia, dysfunction of the PFC has been strongly linked to cognitive dysfunction. PFC functioning however, necessarily relies on interactions within and between networks of interconnected neurons. Across species, the PFC has been anatomically defined as the region of cortex reciprocally connected with the mediodorsal thalamus (MD), a definition that suggests PFC functioning cannot be divorced from that of its main thalamic counterpart. Indeed, an increasing number of studies have demonstrated the involvement of MD in cognitive behaviors. Schizophrenia patients performing cognitive tasks also exhibit decreased MD activity, with growing evidence for decreased functional connectivity with the PFC. The studies presented here seek to build on this literature using the mouse as a model organism. Taking advantage of recent tools for temporally- and spatially-restricted manipulations of neural activity we show that a relatively mild and reversible decrease in MD activity is capable of impairing two cognitive behaviors classically shown to be PFC-dependent – behavioral flexibility and working memory. Simultaneously recording MD and PFC activity while mice perform a spatial working memory task, we show task modulations of synchronous MD-PFC activity that are disrupted by a primary decrease in MD activity. Following up on this finding using pathway-specific manipulations of MD-to-PFC and PFC-to-MD neural connections, we provide behavioral and neurophysiological evidence that these circuits serve as distinct neural substrates for working memory maintenance and retrieval. Together, these findings provide causal evidence in support of an association between thalamo-prefrontal dysfunction and cognitive impairment, and may enable the development of more selective therapeutic strategies for cognitive disorders such as schizophrenia.

Reading requires the successful recruitment and coordination of brain networks to translate visual symbols into phonemes, which are then sequenced to match speech sounds and matched onto semantic representations. Although phonemic awareness is understood to be a core deficit associated with reading disability, neuroimaging has demonstrated an association between poor reading and disruption to various interrelated areas in the brain. This includes one of the major visual pathways, the magnocellular pathway, which contributes to the dorsal pathway in the brain and the processing of motion. For at least two decades, researchers have observed differences in motion processing, supported by the magnocellular pathway, between individuals with and without dyslexia (Eden et al., 1996; Gori et al., 2016; Livingstone et al., 1991; Wilmer, 2004). Further, psychometric studies report an association between reading ability and dorsal stream sensitivity in adults and in children before and after learning to read (Boets et al., 2011; Kevan & Pammer, 2009). Studies of the development of the major visual pathways have suggested that the magnocellular pathway follows a protracted course of development, which raises the possibility that it is vulnerable to pathological change during development and also has the potential for greater plasticity (Armstrong et al., 2002; Stevens & Neville, 2006). To explore the potential differences in early-stage visual processing, this dissertation study investigated whether neurophysiological measures, as indexed by event-related potentials (ERP), may differ between adults with and without dyslexia to stimuli tailored to evoke a response from each of two major visual pathways: magnocellular and parvocellular. The P1 component was elicited in response to motion stimuli designed to probe magnocellular pathways, and the N1 component was elicited in response to color stimuli designed for parvocellular processing. Group comparisons revealed statistically significant group differences in P1 amplitude for the motion/magnocellular condition, but no differences were found for N1 ERP measures for the parvocellular/color condition. Moderate to strong correlations between P1 measures in response to the magnocellular/motion condition were observed in relation to specific behavioral assessments: nonverbal reasoning and memory, orthographic choice, the word identification subtest from the Woodcock Reading Mastery Test (3rd edition: WRMT-III, Woodcock, 2011), and the sight word efficiency subtest from the Test of Word Reading Efficiency (2nd edition: TOWRE-2, Wagner, Torgesen, & Rashotte, 2011). These results are indicative of an early-stage visual processing disruption in individuals with dyslexia observable at the level of the brain. Due to the compounding impact of even small disruptions of sensory and cognitive processing on learning, refining our knowledge of the underlying neural mechanisms of reading may permit earlier identification and potentially more focused interventions that could yield better outcomes for struggling readers. Additionally, the association of those differences with measures of word decoding will inform further research into the underlying neural mechanisms that may contribute to dyslexia and skilled reading.

Investigou-se a gênese de atividade irregular em neurônios de centros geradores de padrões através de modelos eletrofisiologicamente realistas. Para tanto, foram adotadas abordagens paralelas. Primeiramente, desenvolveram-se técnicas para determinar quais os mecanismos biofísicos subjacentes aos processos de codificação de informação nestas células. Também foi proposta uma nova metodologia híbrida (baseada em continuação numérica e em varreduras força bruta) para análise de bancos de dados de modelos neuronais, permitindo estendê-los e revelar instâncias de multiestabilidade entre regimes oscilatórios e quiescentes. Além disto, a fim de determinar a origem de comportamento complexo em modelos neuronais simplificados, empregaram-se métodos geométricos da teoria de sistemas dinâmicos. A partir da análise de mapas unidimensionais perturbados por ruído, foram discutidos possíveis cenários para o surgimento de caos em sistemas dinâmicos aleatórios. Finalmente mostrou-se que, levando em conta o ruído, uma classe de modelos de condutâncias reproduz padrões de disparo observados in vivo. Estas pertubações revelam a riqueza da dinâmica transiente, levando o sistema a visitar um arcabouço determinista complexo preexistente -- sem recorrer a ajustes finos de parâmetros ou a construções ad hoc para induzir comportamento caótico. / We investigated the origin of irregularities in the dynamics of central pattern generator neurons, through analyzing electrophysiologically realistic models. A number of parallel approaches were adopted for that purpose. Initially, we studied information coding processes in these cells and proposed a technique to determine the underlying biophysical mechanisms. We also developed a novel hybrid method (based on numerical continuation and brute force sweeps) to analyze neuronal model databases, extending them and unveiling instances of multistability between oscillatory and resting regimes. Furthermore, in order to determine the origin of irregular dynamics in simplified neuronal models, we employed geometrical methods from the theory of dynamical systems. The analysis of stochastically perturbed maps allowed us to discuss possible scenarios for the generation of chaotic behaviour in random dynamical systems. Finally we showed that, by taking noise into account, a class of conductance based models gives rise to firing patterns akin to the ones observed \\emph{in vivo}. These perturbations unveil the richness of the transient dynamics, inducing the system to populate a preexistent complex deterministic scaffolding -- without resorting to parameter fine-tuning or ad hoc constructions to induce chaotic activity.

A habilidade de se preparar para futuros eventos é essencial para o comportamento. No presente trabalho, investigamos como diferentes formas de expectativa temporal podem modular o processamento de estímulos sensoriais. Por meio de 4 experimentos psicofísicos, sendo 2 com registro eletroencefalográfico (EEG) concomitante, nós estudamos o efeito da ação motora voluntária e da expectativa temporal em diferentes estágios do processamento sensorial. Nossos resultados sugerem que mecanismos ligados à preparação motora influenciam a percepção temporal das consequências desta ação. Além disso, nossos resultados mostraram que a atenção temporal pode modular estágios motores e sensoriais do processamento. Em conjunto, nossos resultados sugerem que expectativas temporais podem influenciar diferentes estágios do processamento principalmente por meio do controle de excitabilidade cortical de regiões do sistema nervoso central ligadas àquela tarefa. / The ability to anticipate future events is essential for behavior. On the present work, we investigated how different forms of temporal expectations can modulate stimuli processing. In four psychophysical experiments (two of them with EEG) we studied how voluntary action and temporal attention can influence processing at different stages. Our results suggest that mechanisms related to motor preparation can bias the temporal perception of the consequences of this action. Moreover, we found that temporal attention can modulate perceptual and motor stages of stimulus processing. Altogether, our results suggest that temporal expectations can influence different levels of target processing, mainly by controlling cortical excitability of task-relevant regions of the central nervous system.

Motor learning is an important component of daily life: humans are constantly adjusting their movements and acquiring new skills in order to meet the demands of their environment. Motor learning also contributes to neurorehabilitation, so it is therefore important to understand the neural mechanisms underlying motor learning so that these mechanisms can be exploited to promote neurorehabilitation after central nervous system injury. This dissertation focuses on three distinct methods of improving motor learning in healthy adults. In Chapter 2, we tested the effects of perturbation schedule on retention of a locomotor adaptation. The results of this work demonstrated that introducing a perturbation slowly and incrementally versus introducing a perturbation abruptly produces similar behavioral expression of locomotor memories across days. In Chapter 3, we tested whether administering 200 mg of caffeine immediately after practicing a novel motor skill enhances retention of that skill 24 hours later. However, we found that post-practice caffeine administration did not significantly improve retention of the motor skill. In combination with previous reports, these results suggest that the effects of post-practice caffeine administration are likely task-specific. In Chapter 4, we examined the interactions between hand use, practice-dependent plasticity and motor learning. We found that experimentally immobilizing the left hand for 8 hours facilitates subsequent practice-dependent changes in corticospinal excitability in a topographically-specific manner. In contrast, immobilization did not facilitate practice-dependent changes in TMS-evoked thumb movements, nor did it promote learning or retention of a ballistic motor skill. Although it is thought that practice-dependent changes in corticospinal excitability are an important and potentially causal contributor to motor memory, the results of this work indicate that experimentally enhancing practice-dependent changes in corticospinal excitability is not sufficient to promote motor learning. In sum, although none of the experimental interventions tested here substantially improved motor learning, these experiments highlight the influence of various mechanisms on motor learning in the intact nervous system.

"July 2002" Includes bibliographical references (leaves 324-342)