Primates, including humans, explore their visual environment with sequences of gaze fixations interrupted by saccadic eye movements that re-orient the fovea to objects of interest. This visual behavior is thought to involve two separate processes. First, the current foveal image is analyzed and the next object of interest is selected as a saccade target. Second, previously examined objects are retained to prevent their re-examination. Visual behavior has been studied successfully using the visual search paradigm, in which subjects locate a unique target stimulus from amongst multiple distracting stimuli. Models of visual search posit that the process of saccade target selection is guided by a visual salience map. This map receives both stimulus-driven and goal-directed inputs to form representations of visual objects, and a competition between those representations is played out to determine the next saccade target. Neurophysiological studies using nonhuman primates have suggested that the salience map is distributed across a network of brain areas that includes the midbrain superior colliculus (SC). These studies, however, have not ruled out the possibility that selective activity for a saccade target may instead be related to the preparation of the saccade. Moreover, not much is known about the selection of a saccade target beyond the first in a sequence of gaze fixations. Finally, the mechanisms underlying the process of saccade target retention are not well understood. In this thesis, I will investigate the role of the primate SC in visual behavior by recording the activity of single neurons while monkeys perform visual search tasks. The major findings will describe 1) how SC sensory-motor neurons instantiate the visual salience map; 2) how this salience map is dynamically updated so that saccade targets are retained; and 3) how multiple representations on this salience map are processed in parallel for saccade target selection. Given SC’s role in the control of visual behavior and its position within the network involved in cognitive processes, these findings have important implications for our understanding of the neural basis of human cognition and of its dysfunctions in disease states. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2010-12-22 09:52:20.143

Behavioural choices of animals as they acquire resources in the wild are well characterized by foraging theory; however, the neural mechanisms underlying these behaviours are not well understood. The goal of this thesis is to understand the brain mechanisms involved in selecting and executing such foraging behaviours. To do so, rhesus monkeys performed a novel visuosaccadic foraging task while we recorded the activity of single neurons in the intermediate layers of the superior colliculus (SCi). An important innovation of this task is that both target profitability – the measure of value in the simplest case of foraging theory – and saccade choice are measured separately. We hypothesized that target profitability is represented in the SCi in addition to its well characterized role in saccade planning and preparation. Visual Foraging Task: Monkeys harvested coloured dots representing prey items by fixating them for a pre-specified handling time. On each trial, multiple prey are presented, sharing identical physical attributes except that each was one of three colours. All prey of the same colour shared the same profitability [Profitability = reward magnitude (ml)/handling time (s)]. According to foraging theory, intake of reward is maximized if prey are selected in descending order of their profitability. Indeed, we found subjects gradually approached optimal efficiency. We computed an index of the relative subjective profitability of each prey colour, which compared the rank order with which monkeys chose prey of each colour. This subjective index of profitability was then compared to concomitant SC activity attributed to the prey item in the neuron’s response field (RF). First, we found that the amount of SC activity reflected the subjective profitability of the RF targets, and established that this effect was not simply a result of saccade goal planning. Second, profitability information remains dominant throughout the handling period until reward delivery, after which activity also became selective for upcoming saccades. Together, our results highlight the prominent role of target profitability in shaping SCi activity. We propose that profitability information in the SCi may play an important role in resolving competition between numerous target representations to choose the next saccade goal. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2011-02-21 15:37:43.468

Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 199-212). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 114-121).

Thesis (Ph. D.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 9, 2007) Vita. Includes bibliographical references.

xiv, 152 p. Adviser: Terry Takahashi (Biology Dept.). Chapter 2 of this dissertation has been previously published in the Journal of Neurophysiology. Citation: Whitchurch EA and Takahashi TT. Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba). J Neurophysiol 96: 730-745, 2006. / A print copy of this title is available through the UO Libraries under the call number: SCIENCE QL696.S85 W54 2006 / Survival depends on our ability to detect and integrate sensory information from multiple modalities, allowing for the most efficient behavioral response. For example, barn owls must combine sights and sounds from the environment to localize potential prey. A vole scurrying through a drift of dried leaves is more likely to meet its doom if a nearby owl can both faintly see and hear it. How does the brain take two physically discreet inputs and combine them into a unified representation of the surrounding multisensory world? Moreover, how is this internal representation transformed into the most efficient behavioral response? This dissertation comprises original research addressing these questions in the barn owl with two distinct approaches: First, Chapters II and III describe orientation behavior in response to auditory, visual, and audiovisual stimuli. Chapter II probes the effect of stimulus strength on saccadic behavior and the nature of audiovisual integration, and was taken from a co-authored publication. Chapter III explores the behavioral consequence of an induced stimulus asynchrony in audiovisual integration and was taken from a co-authored manuscript being prepared for publication. The second experimental approach is described in Chapters IV and V. These chapters probe the physiological basis of saccadic behavior by measuring single-neuron responses to auditory, visual, and audiovisual stimuli. Chapter IV describes how auditory responses of neurons from the external nucleus of the inferior colliculus depend on sound pressure level. Chapter V describes activity of optic tectum neurons in response to auditory, visual, and audiovisual stimuli. The behavioral findings described herein suggest that barn owls often incorporate both the speed of the auditory system and the accuracy of the visual system when localizing a multisensory stimulus, even when the two modalities are presented asynchronously. The physiological studies outlined in this dissertation show that sensory representations in the midbrain can be used to predict general trends in saccadic behavior: Neuronal thresholds were within the range of observed behavioral thresholds. Responses to multisensory stimuli were enhanced relative to unisensory stimuli, possibly corresponding to enhanced multisensory behavior. These data support fundamental rules in multisensory integration that may apply across species.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Psychology, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Vita. / Bibliography: leaves 133-142. / by Bjorn Hellmut Merker. / Ph.D.

As we interact with the world, we must decide what to do next based on previously acquired and incoming information. The study of perceptual decision-making uses highly controlled sensory stimuli and exploits known properties of sensory and motor systems to understand the processes that occur between sensation and action. Even these relatively simple decisions invoke operations like inference, integration of evidence, attention, appropriate action selection, and the assignment of levels of belief or confidence. Thus, the neurobiology of perceptual decision-making offers a tractable way of studying mechanisms that play a role in higher cognitive function. The controlled nature of perceptual decision-making tasks allows an experimenter to infer the latent processes that give rise to a decision. For example, many decisions are well-described by a process of bounded evidence accumulation, in which sensory evidence is temporally integrated until a terminating threshold is exceeded. This thesis improves our understanding of how these latent processes are implemented at the level of neurobiology. After an introduction to perceptual decision-making in Chapter 1, Chapter 2 focuses on the behavioral observations that corroborate whether a subject’s decisions are governed by bounded evidence accumulation. Through simulations of multiple decision-making models, I show that several commonly accepted signatures of evidence accumulation are also predicted by models that do not posit evidence accumulation. I then dissect these models to uncover the features that underlie their mimicry of evidence accumulation. Using these insights, I designed a novel motion discrimination task that was able to better identify the decision strategies of human subjects. In Chapter 3, I explore how the accumulation of evidence is instantiated by populations of neurons in the lateral intraparietal area (LIP) of the macaque monkey. Recordings from single LIP neurons averaged over many decisions have provided support that LIP represents the accumulation of noisy evidence over time, giving rise to diffusion dynamics. However, this diffusion-like signal has yet to be observed directly because of the inability to record from many neurons simultaneously. I used a new generation of recording technology—neuropixels probes optimized for use in primates—to record simultaneously from hundreds of LIP neurons, elucidating this signal for the first time. Through a variety of analyses, I show that the population’s representation of this signal depends on a small subset of neurons that have response fields that overlap the choice targets. Finally, in Chapter 4, I discover a neural mechanism in the midbrain superior colliculus (SC) involved in terminating perceptual decisions. I show that trial-averaged activity in LIP and SC is qualitatively similar, but that single-trial dynamics in each area are distinct. Unlike LIP, SC fired large bursts of activity at the end of the decision, which were sometimes preceded by smaller bursts. Through simultaneous recordings, I uncover the aspects of the diffusion signal in LIP that are predictive of bursting in SC. These observations led me to hypothesize that bursts in SC are the product of a threshold computation involved in terminating the decision and generating the relevant motor response. I confirmed this hypothesis through focal inactivation of SC, which affected behavior and LIP activity in a way that is diagnostic of an impaired threshold mechanism. In total, this work improves our ability to identify the hidden, intermediate steps that underlie decisions and sheds light on their neural basis. All four chapters have been published or posted as separate manuscripts (Steinemann et al., 2022; Stine et al., 2020; Stine et al., 2022; Stine et al., 2019).

No description available.

Certains troubles visuo-moteurs observés dès le stade précoce de la maladie de Parkinson (MP) pourraient être liés à une altération du fonctionnement d’une structure sous-corticale reliée aux ganglions de la base, le colliculus supérieur (CS). L’objectif de cette thèse a été d’explorer l’état fonctionnel du CS chez le patient parkinsonien nouvellement diagnostiqué (de novo) avant et après instauration du traitement dopaminergique, afin d’évaluer son potentiel de biomarqueur. Pour cela, un paradigme expérimental d’Imagerie par Résonance Magnétique fonctionnelle (IRMf) a été développé, permettant d’imager avec succès l’activité fonctionnelle du CS et également du corps genouillé latéral (CGL) et de l’aire visuelle primaire V1 et de moduler leur activité via l’emploi de stimulation visuelle jouant sur de très faibles niveaux de contraste (<10%). Un test de psychophysique a également été développé, permettant d’estimer la réponse perceptuelle au contraste. Nous avons dans un premier temps testé notre protocole expérimental auprès de sujets sains d’âge variable afin d’évaluer le fonctionnement de ces trois régions d’intérêt (ROIs) au cours du vieillissement normal et de différencier les effets liés à l’âge de ceux potentiellement liés à la pathologie (Etude 1). Une diminution statistiquement significative de la réponse BOLD au sein du CGL et de V1 avec l’âge a été observée, ces réponses corrélant de plus parfaitement avec les réponses perceptuelles estimées en psychophysique. Les voies magnocellulaire et parvocellulaire semblent jouer un rôle dans cette perte de sensibilité au contraste de luminance liée à l’âge. Nous avons dans un second temps testé notre protocole auprès de patients parkinsoniens de novo avant et après instauration du premier traitement dopaminergique afin d’évaluer les effets de la MP et du traitement sur le fonctionnement de nos ROIs (Etude 2). Une altération précoce du traitement du contraste a été observée au sein du CS et du CGL chez les patients parkinsoniens, non normalisée par l’instauration du traitement dopaminergique. Ces travaux de thèse ont ainsi mis en évidence un déficit fonctionnel du CS et du CGL survenant précocement durant l’évolution de la MP, confirmé par nos analyses de connectivité effective. Ces résultats pourraient favoriser l’identification de déficits liés à un dysfonctionnement sensoriel de ces structures tout comme le développement de tests paraclinique et clinique impliquant ce système pour un diagnostic plus précoce de la maladie. / Some visuo-motor impairments observed in the early stages of Parkinson’s disease (PD) might be related to a dysfunction of a subcortical structure connected to the basal ganglia, the superior colliculus (SC). The aim of this PhD thesis was to explore the functional state of the SC in newly diagnosed (de novo) PD patients before and after dopaminergic treatment intake, in order to evaluate the potential value of the SC functioning as a biomarker. To do this, we developed a functional Magnetic Resonance Imaging (fMRI) experimental protocol, which successfully imaged the SC and also the lateral geniculate nucleus (LGN) and primary visual area V1 functional activity and modulate their activity by using visual stimuli with low luminance contrast levels (<10%). Additionally, we estimated the perceptual response to contrast by using a psychophysical task. We tested in a first time this experimental protocol on healthy subjects with varying age in order to evaluate the effect of normal aging on the functioning of these regions of interest (ROIs) and to distinguish the effects related to age from those potentially related to the pathology (Study 1). A significant progressive decrease of the BOLD amplitude with age was observed in the LGN and V1. These data were consistent with the response functions obtained with the psychophysical task. These results indicate a significant luminance contrast sensitivity decline with age of both the magnocellular and parvocellular pathways. In a second time, we tested our protocol on de novo PD patients before and after the introduction of the first dopaminergic treatment in order to assess the effects of PD and treatment on the ROIs functioning (Study 2). Our results highlighted an early alteration of the contrast processing for the SC and LGN in PD patients, with no normalization after dopaminergic treatment introduction. These findings indicate a functional deficit of the SC and LGN that appears early in the disease course, in line with our effective connectivity analyses. These results could favor the identification of deficits linked to sensory dysfunction of these structures as well as the development of paraclinical and clinical tests involving this system for an early diagnosis of the disease.