The proportion of elderly individuals in society is increasing dramatically, leading to an increase in the prevalence of age-related neurological disorders that affect the function of the frontal lobes and overall movement control. This thesis aims to evaluate ‘executive control’ and the underlying brain changes in normal versus abnormal aging processes using saccadic eye movement tasks. Tasks performed by subjects that probe executive control consist of antisaccades (generate a voluntary eye movement after inhibiting an automatic movement to a visual stimulus), and memory-guided saccades (generate eye movements to three previous remembered visual stimuli in the same sequence they were presented). Both of these types of saccades require good functioning behavioural control, which is subserved by areas in the prefrontal cortex. This thesis specifically characterizes the changes in oculomotor control related to aging, Huntington’s disease, mild cognitive impairment (amnestic), and Alzheimer’s disease. We also specifically examine the neural mechanisms related to behavioural control in the antisaccade task in aging. Together, the conclusions drawn from this thesis reveal that specific areas in the prefrontal cortex are involved in executive dysfunction in both normal and abnormal aging, but the patient groups studied have provided new understanding that different underlying brain substrates may be altering function in the frontal cortical areas, such as the basal ganglia and the hippocampus. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2011-04-28 13:44:32.25

An important function of the brain is to inhibit irrelevant behaviors. This thesis examines the role of the basal ganglia in response suppression using saccadic eye movements as a model of behavior. We measured the activity of single saccade-related neurons in primate Substantia Nigra pars reticulata (SNr), a main output structure of the basal ganglia, while the context surrounding the initiation and suppression of saccades was manipulated. Inserting a temporal gap of no stimuli between the disappearance of a central visual fixation point and the appearance of a peripheral visual target leads to a reduction in saccadic reaction times (SRT); the ‘gap’ effect. SNr pause neurons decreased their activity during the gap and this decrease correlated with SRT. This finding suggests the SNr may contribute directly to producing the gap effect and that signals related to the effect are propagating through a frontal-basal ganglia circuitry to impact pre-saccade processing. Interleaving pro-saccade (look towards a visual stimulus) and anti-saccade (look away from visual stimulus) trials allowed us to investigate how neural processes change when preparing to suppress a saccade instead of making one automatically. We show that SNr neurons exhibit activity consistent with both suppression of automatic responses and facilitation of voluntary responses, during anti-saccades. These data provide direct neurophysiological evidence for a dual role of inhibitory and disinhibitory basal ganglia outputs in the flexible shaping of behavior. Parkinson’s disease (PD) is a neurodegenerative disorder that impairs motor function due to depletion of dopamine in the striatum. Using an oculomotor countermanding paradigm, we found that PD patients were unable to suppress saccades to a peripheral target, providing evidence that the SNr performs a gating function that mediates the initiation and suppression of saccades. When pathology to the circuitry occurs, inhibitory control over saccades is affected. In Conclusion, using a variety of behavioral contexts, this thesis has demonstrated that the basal ganglia, specifically the SNr, mediates the suppression and voluntary initiation of saccades, possibly via an inhibitory gating mechanism, and that this role is important for successful interaction with a dynamic environment. / Thesis (Ph.D, Physiology) -- Queen's University, 2008-07-16 12:06:19.188

We live in a rich visual world that we experience as a seamless and detailed stream of continuous information. However, we can only attend to and remember a small portion of our visual environment. The visual system is tasked with stitching together snapshots of the world through near constant eye movements, with around three saccades per second. The situation is further complicated with the visual system being contralaterally organized. Each eye movement can bring items in our environment into a different visual hemifield. Despite the many challenges and limitations of attention and the visual system, how does the brain stitch together our experience of our visual environment? One potential mechanism that could contribute to our conscious perception of a continuous visual experience could be visual working memory (VWM) working to maintain representations of items across saccades. Electrophysiological activity using event-related potentials has revealed the contralateral delay activity (CDA), which is a sustained negativity contralateral to the side of the visual field where subjects are attending. However, how does this work if we are constantly moving our eyes? How do we form a stable representation of items across eye movements? Does the representation transfer over to the other side of the brain, constantly shuffling the items between the hemispheres? Or does it stay in the hemisphere contralateral to the visual field where the items were located when we originally created the representation? The consequences of eye movements need to be examined at multiple levels and time points throughout the process. The goal of my doctoral dissertation is to investigate VWM representations throughout the dynamic peri-saccadic window. In Experiment 1, I will first compare VWM representations across shifts of attention and eye position. With the focus on the effect of maintaining attention on items across eye movements, Experiment 2 will also explore eye movements both towards and away from attended visual hemifields. Finally, Experiment 3 is designed to substantiate our use of the CDA as a tool for examining VWM representations across eye movements by confirming that the CDA is indeed established in retinotopic coordinates.

The most common evidence for inhibition of return (IOR) is the robust finding of increased response times to targets that appear at previously cued locations following a cue-target interval exceeding ~ 300 ms. In a variation on this paradigm, Abrams and Dobkin (1994a) observed that IOR was greater when a saccadic response was made to a peripheral than to a central arrow, leading to the conclusion that saccadic responses to peripheral targets comprise motoric and perceptual components (the two components theory for IOR) whereas saccadic responses to a central target comprise a single motoric component. In contrast to the foregoing findings, Taylor and Klein (2000) discovered that IOR for saccadic responses was equivalent for randomly intermixed central and peripheral targets, suggesting a single motoric flavor under these conditions. To resolve the apparent discrepancy, a strict replication of Abrams and Dobkin was conducted in which central and peripheral targets were either blocked or mixed. In the blocked design, peripheral targets resulted in more IOR than central targets, while in the mixed design, replicating Taylor and Klein (2000), target type had no bearing on the magnitude of IOR (i.e., equivalent IOR was obtained for both target types). This pattern of results suggests that the confound inherent in Abrams and Dobkin's blocked design generated a pattern of results that "masqueraded" as two components of IOR.

Background: The central nervous system (CNS) dysfunction resulting from prenatal alcohol exposure (PAE) is the most debilitating aspect of fetal alcohol spectrum disorders (FASDs). Affected children exhibit numerous cognitive and behavioural deficits which can severely affect quality of life. As the diagnosis of FASDs often requires specially trained physicians, there is a need for sensitive and specific tools that screen PAE-related CNS dysfunction in order to identify individuals who require further consultation. Additionally, objective measures of intervention end-points are critical to assess potential treatments for this population. As saccadic eye movement behaviours reflect the integrity of multiple brain structures, a battery of oculomotor tasks may serve both these functions. This study sought to test the hypothesis that oculomotor performance in FASD would differ from typically developing children and would allow the objective measure of cognitive improvements resulting from a strength-based motor skills intervention. Methods: A cohort of 31 children with FASD, and 31 age- and sex-matched controls completed prosaccade, antisaccade, delayed memory-guided sequential (DMS) and predictive eye movement tasks. Additionally, a selection of these children were involved in an intervention study and therefore tested on three separate occasions using the eye movement tasks and computerized neuropsychological tests. Results: Compared to controls, children with FASDs elicited increased direction and anticipatory errors in the antisaccade task, increased timing and sequence errors in the DMS task, and increased anticipatory and decreased express saccades in the predictive task. The FASD group also exhibited an increase in the error of saccade trajectories in the pro- and antisaccade tasks, in addition to increased velocities of visually-guided saccades in the predictive task. Furthermore, those involved in the intervention study improved in measures of response inhibition in the DMS task. Conclusion: This study indicates that frontostriatal and cerebellar dysfunction can be assessed in children with FASDs using a battery of eye movement tasks. In addition, children involved in the strength-based motor skills intervention improved in the ability to perform complex oculomotor tasks. These findings suggest that select eye movement tasks may be utilized to identify CNS dysfunction in FASD and to measure cognitive improvements resulting from behavioural interventions. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2010-08-17 09:55:59.382

The ability to process and respond to environmental cues requires the transformation of a sensory stimulus into an appropriate motor response, a process known as a sensorimotor transformation. The anti-saccade task can be used to investigate the ability of a subject to suppress a reflexive saccade towards a visual stimulus (pro-saccade) and generate a voluntary saccade 180° away from it. Additional steps are involved in the anti-saccade sensorimotor transformation that do not occur in the pro-saccade, which may produce performance differences between pro- and anti-saccade metrics. We were interested in exploring these differences to gain insight on the mechanism of the sensorimotor transformation of the anti-saccade and to uncover any directional biases in saccadic performance. Two experiments were performed, one in which stimuli were presented at 20 angular positions with a constant eccentricity of 12°, and another using 18 possible eccentricities along the horizontal. Pro-saccades had faster SRTs and velocities, larger amplitudes, higher accuracy and less variation in their trajectories than anti-saccades. Pro- and anti-saccade performance was shown to exhibit a similar dependence on both saccade goal direction and eccentricity. Differences manifested as a generalized reduction in anti-saccade performance that can be described as a scalar multiple of pro-saccade performance at all locations. Possible causes of this reduced performance were speculated to be i) the involvement of higher cortical structures, ii) errors in the internal representation of the stimulus, iii) sensorimotor coordinate transformation inaccuracy, and iv) online updating of the motor plan and the speed accuracy trade off inherent to saccades. The results of this study are comparable to previous monkey and human studies however certain differences were found that require further investigation. Further investigation is also required to determine the validity of the possible causes of performance reduction in the anti-saccade task and their specific contributions. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2011-09-08 16:31:18.398

L'interaction des individus avec l'environnement statique ou dynamique nécessite une exploration détaillée et précise des objets. Pour cela, notre système oculomoteur produit des mouvements oculaires rapides et précis appelés « saccades » afin de ramener l’image des objets d’intérêt sur la petite zone centrale de notre rétine (fovéa). Toutefois, notre système oculomoteur est fréquemment exposé à des perturbations physiologiques ou pathologiques. Ces changements sont contrôlés en permanence par des processus sensori moteurs basés sur la plasticité neuronale et appelés adaptation saccadique. L’objectif de mes travaux de thèse est de mieux comprendre les caractéristiques de cette adaptation et sa rétention à long terme mais aussi les réseaux impliqués dans l’adaptation saccadique. Comme les saccades oculaires ont un lien étroit avec l’attention visuo-spatiale, notre intérêt s’est également porté sur les interactions qui peuvent exister avec les réseaux impliqués dans le contrôle de l’attention visuo-spatiale. Un des principaux résultats est que l’orientation de l’attention exogène covert -sans bouger les yeuxdans des taches de détection et de discrimination est améliorée après l’adaptation des saccades réactives. Ces données fondamentales pourraient mener au développement de nouvelles méthodes de rééducation des déficits visuo-attentionnels / The interaction of human beings with their static or dynamic environment requires detailed and precise exploration of objects. For this, our oculomotor system produces fast and accurate eye movements called "saccades" to bring the image of objects of interest on the small central area of the retina (fovea). However, our oculomotor system is frequently exposed to physiological or pathological disturbances. These changes are continuously monitored by sensorimotor processes based on neuronal plasticity and called "saccadic adaptation". The aim of my thesis is to better understand the characteristics of this adaptation and its long-term retention but also the neural networks involved in saccadic adaptation. As saccadic eye movements are closely related to visuo-spatial attention our work has also addressed the interactions that may exist with the networks involved in the control of visuo-spatial attention. A major result revealed that the orientation of the 'covert' exogenous attention -without moving the eyes- in detection and discrimination tasks is improved after adaptation of reactive saccades. These basic data could give rise to the development of new rehabilitation methods in visual-attention deficits

Mindfulness practice is associated with reduced anxiety, enhanced tolerance of negative affect, lower stress reactivity, improved task concentration, increased cognitive flexibility, and enhanced neurological functioning. However, mindfulness-based treatments are highly varied in duration, type and extent or training provided, and treatment focus. Studies of mindfulness interventions also often fail to operationally define mindfulness, which poses a challenging for understanding the mechanism(s) of change involved in its anxiolytic effects. In the current study, attentional control was examined as a possible mechanism of change, as it is largely deficient in individuals with anxiety yet necessary for extinction learning in treatment. In theory, mindfulness interventions can facilitate increased attentional control during exposure tasks, thereby enhancing new learning and eventually improving treatment outcomes. Using a randomized controlled design, the current study aimed to investigate the effects of mindfulness on attentional control for anxious individuals, with a specific examination of two types of mindfulness exercises: mindful physiological awareness and mindful acceptance. 142 participants were recruited from undergraduate psychology classes at Southern Illinois University, of which 63 had moderate-high trait anxiety and 79 had low trait anxiety (per STAI-Trait score). All participants completed baseline self-report questionnaires, after which they completed a mixed saccade task followed by listening to a 15-minute audio-recorded intervention based on group assignment. Finally, they completed a post-test mixed saccade task and post-test self-report questionnaires. It was hypothesized that both mindfulness groups would demonstrate significantly improved inhibition and shifting processing efficiencies compared to a mind wandering control, and that the mindful acceptance group would demonstrate significantly greater gains than the mindful physiological awareness group. Minimal differences in performance effectiveness were expected among all groups. Contrary to hypotheses, results indicated no significant effects of group on inhibition and shifting processing efficiencies or performance effectiveness in the anxious subsample. However, in the non-anxious subsample, the mindful acceptance group had shorter reaction times than the other two groups and the mindful physiological awareness group had higher accuracy rates than the control group. Findings suggest anxious individuals may need more extensive mindfulness practice to improve attentional control, as they tend to display greater attention deficits than non-anxious individuals. However, the study was limited in sample size and further research and study replication is needed prior to making conclusions about whether attentional control is a true mechanism of change. Study limitations, strengths, and future directions for study are also discussed.

Purpose: The aim of the study was to delineate differences in saccade characteristics between a population of athletes and non athletes. Aspects specifically investigated were latency, accuracy, peak velocity, and gain adaptation of saccades using both increasing and decreasing paradigms. Methods: A sample of 28 athletes (varsity badminton and squash players) and 18 non athletes (< 3 hour/week in sports) were studied. Eye movements were recorded at 120Hz using a video based eye tracker (ELMAR 2020). Each subject participated in 2 sessions on separate days. Baseline saccade responses to dot stimuli were measured in both sessions (stimulus size: 5-25 deg). The first session involved a gain decreasing paradigm, induced by displacing the stimulus backwards by 3 degrees from the initial target step (12 deg) for 500 trials. In the 2nd session a gain increase was induced by displacing the stimuli by 3 degrees in the forward direction. The latency and accuracy were calculated from the baseline. The asymptotic peak velocity was calculated from the main sequence (amplitude vs. peak velocity). The amplitude gains, calculated from the adaptation phase, were averaged for every 100 saccade responses. The averaged gains were normalized with respect to the baseline, fitted with a 3rd order polynomial, and differentiated to obtain the rate of change. Differences between the groups were compared using a regression analysis. Results: There were no significant differences in latency, accuracy, and asymptotic peak velocity between athletes and non athletes. No significant differences were seen between the two groups in the magnitude of saccadic adaptation, both for decreasing (- 15% in both groups) and increasing (athletes + 7% and non athletes + 5%) paradigms. However, athletes showed a significantly faster rate of adaptation for the gain increasing paradigm (F = 17. 96[3,6]; p = 0. 002). A significant difference was not observed in the rate of adaptation for the gain decreasing adaptation (F = 0. 856[3,6]; p = 0. 512). Conclusions: The study showed that the athletes do not respond better in terms of reaction time or accuracy of saccades. The significant difference in the rate of change of adaptation between the groups shows that online modification of saccades in the positive direction, although not greater in magnitude, occurs quicker in athletes than non athletes.

Intercepter une cible en mouvement est un défi spatiotemporel relevé par de nombreuses espèces animales. Ici, nous nous sommes intéressés à la capture fovéale lors de l’orientation saccadique du regard vers une cible visuelle mobile chez le singe vigile. La théorie actuelle propose que l’interception saccadique fasse intervenir deux voies neuronales. Une première voie acheminerait, via le colliculus supérieur profond (CSp), un signal de position échantillonnée au générateur saccadique. La seconde, via le cervelet, fournirait une commande supplémentaire sur la base des signaux de mouvement visuel. Une étude comportementale a été réalisée afin d’analyser la dynamique de l’influence de ces signaux sur la trajectoire saccadique et a permis de mettre en évidence une influence continue. Dans une seconde étude, nous avons testé la robustesse du système oculomoteur à une perturbation spatiotemporelle inattendue (par microstimulation électrique du CSp) et montré la présence de saccades de correction précises. L’ensemble de nos résultats plaide pour une représentation continue du but des saccades d’interception. / Intercepting a visual moving target is a spatiotemporal challenge for the brain achieved by various species. Here, we investigated the foveal capture of a moving target by saccadic gaze shifts in the awake monkey. The current theory proposes that the saccadic interception involves two neural pathways. A first pathway would convey to the saccade burst generator a sampled target position signal through the superior colliculus (SC). The second one, through the cerebellum, would convey an additional command on the basis of motion-related signals. A behavioral experiment was performed to analyze the influence of motion-related signals on the saccade dynamics and allowed showing a continuous influence. In a second study, we tested the robustness of the oculomotor system to an unexpected spatiotemporal perturbation (by electrical microstimulation in the deep SC) and showed the presence of accurate correction saccades. Our results argue for a continuous representation of the saccade goal.