Our sensory experiences are encoded in the patterns of activity of the neurons in our brain. While we know we are capable of sensing and responding to a constantly changing sensory environment, we often study neural activity by repeatedly presenting the same stimulus and analyzing the average neural response. It is not understood how the average neural response represents the dynamic neural activity that produces our perceptions. In this work, we use functional imaging of the rodent primary somatosensory cortex, specifically the whisker representations, and apply classic signal-detection methods to test the predictive power of the average neural response. Stimulus features such as intensity are thought to be perceptually separable from the average representation; however, we show that stimulus intensity cannot be reliably decoded from neural activity from only a single experience. Instead, stimulus intensity was encoded only across many experiences. We observed this probabilistic neural code in multiple classic sensory paradigms including complex temporal stimuli (pairs of whisker deflections) and multi-whisker stimuli. These data suggest a novel framework for the encoding of stimulus features in the presence of high-neural variability. Specifically we suggest that our brains can compensate for unreliability by encoding information redundantly across cortical space. This thesis predicts that a somatosensory stimulus is not encoded identically each time it is experienced; instead, our brains use multiple redundant pathways to create a reliable sensory percept.

abstract: Prosthetic users abandon devices due to difficulties performing tasks without proper graded or interpretable feedback. The inability to adequately detect and correct error of the device leads to failure and frustration. In advanced prostheses, peripheral nerve stimulation can be used to deliver sensations, but standard schemes used in sensorized prosthetic systems induce percepts inconsistent with natural sensations, providing limited benefit. Recent uses of time varying stimulation strategies appear to produce more practical sensations, but without a clear path to pursue improvements. This dissertation examines the use of physiologically based stimulation strategies to elicit sensations that are more readily interpretable. A psychophysical experiment designed to investigate sensitivities to the discrimination of perturbation direction within precision grip suggests that perception is biomechanically referenced: increased sensitivities along the ulnar-radial axis align with potential anisotropic deformation of the finger pad, indicating somatosensation uses internal information rather than environmental. Contact-site and direction dependent deformation of the finger pad activates complimentary fast adapting and slow adapting mechanoreceptors, exhibiting parallel activity of the two associate temporal patterns: static and dynamic. The spectrum of temporal activity seen in somatosensory cortex can be explained by a combined representation of these distinct response dynamics, a phenomenon referred in this dissertation to “biphasic representation.” In a reach-to-precision-grasp task, neurons in somatosensory cortex were found to possess biphasic firing patterns in their responses to texture, orientation, and movement. Sensitivities seem to align with variable deformation and mechanoreceptor activity: movement and smooth texture responses align with potential fast adapting activation, non-movement and coarse texture responses align with potential increased slow adapting activation, and responses to orientation are conceptually consistent with coding of tangential load. Using evidence of biphasic representations’ association with perceptual priorities, gamma band phase locking is used to compare responses to peripheral nerve stimulation patterns and mechanical stimulation. Vibrotactile and punctate mechanical stimuli are used to represent the practical and impractical percepts commonly observed in peripheral nerve stimulation feedback. Standard patterns of constant parameters closely mimic impractical vibrotactile stimulation while biphasic patterns better mimic punctate stimulation and provide a platform to investigate intragrip dynamics representing contextual activation. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2017

Recent studies have shown that neuronal connections occur between primary auditory and visual cortices of the primate (Falchier et al., 2002; Rockland and Ojima, 2003), and it has been suggested that these projections are involved in multisensory processing in these lower-level, core areas of cortex. The present study was conducted to determine if similar connections occur in other higher mammals such as carnivores (ferrets; Mustela putorius). Large injections of sensitive neuroanatomical tracer were placed within the core areas of auditory cortex in 3 ferrets. After transport and processing, labeled axon terminals were found not in primary visual cortex, but in area 19, or V3. Injection of tracer into V3 of 3 additional ferrets produced retrogradely labeled neurons not in the core region of auditory cortex, but along its posterior borders. These data indicate that cross-modal connections occur in the ferret cortex, but do not support the notion that they exist between the primary representations of the different sensory modalities.

UNIQUE FEAUTRES OF ORGANIZATION AND NEURONAL PROPERTIES IN A MULTISENSORY CORTEX Multisensory processing is a ubiquitous sensory effect that underlies a wide variety of behaviors, such as detection and orientation, as well as perceptual phenomena from speech comprehension to binding. Such multisensory perceptual effects are presumed to be based in cortex, especially within areas known to contain multisensory neurons. However, unlike their lower-level/primary sensory cortical counterparts, little is known about the connectional, functional and laminar organization of higher-level multisensory cortex. Therefore, to examine the fundamental features of neuronal processing and organization in the multisensory cortical area of the posterior parietal cortex (PPr) of ferrets, the present experiments utilized a combination of immunohistological, neuroanatomical and multiple single-channel electrophysiological recording techniques. These experiments produced four main results. First, convergence of extrinsic inputs from unisensory cortical areas predominantly in layers 2-3 in PPr corresponded with the high proportion of multisensory neurons in those layers. This is consistent with multisensory responses in this higher-level multisensory region being driven by cortico-cortical, rather than thalamo-cortical connections. Second, the laminar organization of the PPr differed substantially from the pattern commonly observed in primary sensory cortices. The PPr has a reduced layer 4 compared to primary sensory cortices, which does not receive input from principal thalamic nuclei. Third, the distribution of unisensory and multisensory neurons and properties differs significantly by layer. Given the laminar-dependent input-output relationships, this suggests that unisensory and multisensory signals are processed in parallel as they pass through the circuitry of the PPr. Finally, specific functional properties of bimodal neurons differed significantly from those of their unisensory counterparts. Thus, despite their coextensive distribution within cortex, these results differentiate bimodal from unisensory neurons in ways that have never been examined before. Together these experiments represent the first combined anatomical-electrophysiological examination of the laminar organization of a multisensory cortex and the first systematic comparison of the functional properties of bimodal and unisensory neurons. These results are essential for understanding the neural bases of multisensory processing and carry significant implications for the accurate interpretation of macroscopic studies of multisensory brain regions (i.e. fMRI, EEG), because bimodal and unisensory neurons within a given neural region can no longer be assumed to respond similarly to a given external stimulus.

Embora o uso do sistema âncora reduza a oscilação corporal em idosos, ainda não está claro como a informação háptica adicional interage com os outros sistemas sensoriais. Assim, o objetivo deste estudo foi avaliar a contribuição do sistema âncora na oscilação corporal de idosos durante a postura ereta semi estática com diferentes manipulações sensoriais: visão (com e sem) e somatossensação (superfície rígida e de espuma). Trinta idosos participaram desse estudo. Eles foram instruídos a ficar em pé sobre uma plataforma de força, com os pés afastados na largura do ombro. Três fatores foram manipulados: uso do sistema âncora, disponibilidade de visão e textura da superfície de suporte. O sistema âncora é constituído de dois cabos flexíveis seguros pelas mãos com cargas de 125 g conectados a cada extremidade que fica em contato com o solo. Nas tentativas sem visão, os participantes fecharam os olhos e uma venda foi colocada sobre os olhos. Na situação de olhos abertos os participantes fixaram o olhar em um alvo posicionado na altura dos olhos. Para a manipulação da textura da superfície, uma espuma com as dimensões da plataforma de força foi colocada sobre a mesma. Na condição de superfície rígida, os participantes permaneceram em contato diretamente com a superfície da plataforma de força. Com base no deslocamento do centro de pressão (CP), foram calculadas as seguintes variáveis: área da elipse contendo 95% dos dados do deslocamento do CP, amplitude média de oscilação (AMO) e velocidade média de oscilação (VMO) para quantificar a oscilação corporal. Os resultados da análise estatística para a área da elipse e para a VMO revelaram efeito principal de âncora (p<=0,0001), visão (p<=0,0001) e superfície (p<=0,0001), assim como interação entre visão e superfície (p<=0,0001) e âncora e superfície (p=0,002). Para a AMO os resultados revelaram efeito principal de âncora (p<=0,0001), visão (p<=0,0001) e superfície (p<=0,0001) e interação entre visão e superfície (p<=0,0001). O uso da âncora reduziu a oscilação corporal nas três variáveis analisadas. Por outro lado, a ausência de visão e a superfície de espuma aumentaram a oscilação corporal. O uso da âncora não contribuiu para reduzir a oscilação corporal na superfície rígida. Porém, na superfície de espuma o uso da âncora reduziu a oscilação corporal. O sistema âncora contribuiu para reduzir a oscilação corporal e essa redução foi mais efetiva quando o participante estava sobre a superfície de espuma. Portanto, conclui-se que em situações mais desafiadoras o uso do sistema âncora parece ser mais efetivo / Although the use of the anchor system reduces body sway in older adults, it is not clear how the additional haptic information interacts with other sensory systems. The purpose of this study was to evaluate the anchor system contribution to postural sway in older adults during a quiet standing task with different sensory manipulations: vision (with and without) and somatosensation (with and without a foam on the support surface). Thirty individuals participated in this study. They stood on a force plate, with their feet apart at shoulder width. Three factors were manipulated: use of the anchor system, vision availability and support surface texture. The anchor system consists of two flexible cables hold by the hands with loads of 125 g connected to each end that is in contact with the ground. In the trials without vision, participants closed their eyes and a blindfold was placed over their eyes. In the eyes open condition, participants fixed their gaze on a target positioned at eye level. For the manipulation of texture of the surface, a foam with the dimensions of the force plate was placed over it. In the rigid surface condition, participants stood directly over the surface of the force plate. Based on center of pressure (CP) displacement, the following variables were calculated: 95% ellipse area, mean sway amplitude (MSA), and mean sway velocity (MSV). The statistical analysis results for the ellipse area and MSV showed main effect of anchor (p<=0.0001), vision (p<=0.0001) and surface (p<=0.0001), as well as interaction between vision and surface (p<=0.0001) and anchor and surface (p=0.002). For MSA, the results revealed main effect of anchor (p<=0.0001), vision (p<=0.0001) and surface (p<=0.0001) and interaction between vision and surface (p<=0.0001). The use of the anchor reduced body sway in all three variables analyzed. Moreover, the absence of vision and the foam surface increased body sway. The use of the anchor did not contribute to reduce body sway on the rigid surface, but on the foam surface the use of anchor reduced body sway. The anchor system helped reducing body sway and this reduction was more effective when the participant was on the foam surface. Therefore, it follows that in more challenging situations the use of the anchor system appears to be more effective.

No description available.

Embora o uso do sistema âncora reduza a oscilação corporal em idosos, ainda não está claro como a informação háptica adicional interage com os outros sistemas sensoriais. Assim, o objetivo deste estudo foi avaliar a contribuição do sistema âncora na oscilação corporal de idosos durante a postura ereta semi estática com diferentes manipulações sensoriais: visão (com e sem) e somatossensação (superfície rígida e de espuma). Trinta idosos participaram desse estudo. Eles foram instruídos a ficar em pé sobre uma plataforma de força, com os pés afastados na largura do ombro. Três fatores foram manipulados: uso do sistema âncora, disponibilidade de visão e textura da superfície de suporte. O sistema âncora é constituído de dois cabos flexíveis seguros pelas mãos com cargas de 125 g conectados a cada extremidade que fica em contato com o solo. Nas tentativas sem visão, os participantes fecharam os olhos e uma venda foi colocada sobre os olhos. Na situação de olhos abertos os participantes fixaram o olhar em um alvo posicionado na altura dos olhos. Para a manipulação da textura da superfície, uma espuma com as dimensões da plataforma de força foi colocada sobre a mesma. Na condição de superfície rígida, os participantes permaneceram em contato diretamente com a superfície da plataforma de força. Com base no deslocamento do centro de pressão (CP), foram calculadas as seguintes variáveis: área da elipse contendo 95% dos dados do deslocamento do CP, amplitude média de oscilação (AMO) e velocidade média de oscilação (VMO) para quantificar a oscilação corporal. Os resultados da análise estatística para a área da elipse e para a VMO revelaram efeito principal de âncora (p<=0,0001), visão (p<=0,0001) e superfície (p<=0,0001), assim como interação entre visão e superfície (p<=0,0001) e âncora e superfície (p=0,002). Para a AMO os resultados revelaram efeito principal de âncora (p<=0,0001), visão (p<=0,0001) e superfície (p<=0,0001) e interação entre visão e superfície (p<=0,0001). O uso da âncora reduziu a oscilação corporal nas três variáveis analisadas. Por outro lado, a ausência de visão e a superfície de espuma aumentaram a oscilação corporal. O uso da âncora não contribuiu para reduzir a oscilação corporal na superfície rígida. Porém, na superfície de espuma o uso da âncora reduziu a oscilação corporal. O sistema âncora contribuiu para reduzir a oscilação corporal e essa redução foi mais efetiva quando o participante estava sobre a superfície de espuma. Portanto, conclui-se que em situações mais desafiadoras o uso do sistema âncora parece ser mais efetivo / Although the use of the anchor system reduces body sway in older adults, it is not clear how the additional haptic information interacts with other sensory systems. The purpose of this study was to evaluate the anchor system contribution to postural sway in older adults during a quiet standing task with different sensory manipulations: vision (with and without) and somatosensation (with and without a foam on the support surface). Thirty individuals participated in this study. They stood on a force plate, with their feet apart at shoulder width. Three factors were manipulated: use of the anchor system, vision availability and support surface texture. The anchor system consists of two flexible cables hold by the hands with loads of 125 g connected to each end that is in contact with the ground. In the trials without vision, participants closed their eyes and a blindfold was placed over their eyes. In the eyes open condition, participants fixed their gaze on a target positioned at eye level. For the manipulation of texture of the surface, a foam with the dimensions of the force plate was placed over it. In the rigid surface condition, participants stood directly over the surface of the force plate. Based on center of pressure (CP) displacement, the following variables were calculated: 95% ellipse area, mean sway amplitude (MSA), and mean sway velocity (MSV). The statistical analysis results for the ellipse area and MSV showed main effect of anchor (p<=0.0001), vision (p<=0.0001) and surface (p<=0.0001), as well as interaction between vision and surface (p<=0.0001) and anchor and surface (p=0.002). For MSA, the results revealed main effect of anchor (p<=0.0001), vision (p<=0.0001) and surface (p<=0.0001) and interaction between vision and surface (p<=0.0001). The use of the anchor reduced body sway in all three variables analyzed. Moreover, the absence of vision and the foam surface increased body sway. The use of the anchor did not contribute to reduce body sway on the rigid surface, but on the foam surface the use of anchor reduced body sway. The anchor system helped reducing body sway and this reduction was more effective when the participant was on the foam surface. Therefore, it follows that in more challenging situations the use of the anchor system appears to be more effective.

No description available.

No description available.

<p>Many daily motor tasks involve the precise control of both force level and motor timing. The neural mechanisms concurrently managing these movement parameters remain unclear, as the dominant focus of previous literature has been to examine each in isolation. As a result, little is understood regarding the contribution of various sensory modalities to force output and interval production in sequential motor tasks. This thesis uses a sequential force production task to investigate the roles of visual and somatosensory feedback in the timed control of force. In Chapter 2 we find that removal of visual force feedback resulted in specific force output errors, but leaves motor timing behavior relatively unaffected according to predictions of the two-level timing model by Wing and Kristofferson (1973). In Chapter 3, we show that force output errors exhibited in the absence of a visual reference may be related to the processing of reafferent somatosensation from self-generated force pulses. The results of Chapter 4 reveal evidence that force errors exhibited following visual feedback removal are consistent with a shift in the perceived magnitude of force output and that the direction of error may be determined by prior task constraints. In Chapter 5 we find evidence of effector-specificity in the processing of and compensation for reafferent somatosensation. Lastly, in Chapter 6 we find that the interplay between audition and somatosensation in the control of sound level by the vocal effectors resembles that which is observed between vision and somatosensation in the control of force by the distal effectors.</p> / Doctor of Philosophy (PhD)