Spatial navigation deficits — overlooked cognitive marker for preclinical Alzheimer disease?

Detection of incipient Alzheimer disease (AD) pathophysiology is critical to identify preclinical individuals and target potentially disease-modifying therapies towards them. Current neuroimaging and biomarker research is strongly focused in this direction, with the aim of establishing AD fingerprints to identify individuals at high risk of developing this disease. By contrast, cognitive fingerprints for incipient AD are virtually non-existent as diagnostics and outcomes measures are still focused on episodic memory deficits as the gold standard for AD, despite their low sensitivity and specificity for identifying at-risk individuals. This Review highlights a novel feature of cognitive evaluation for incipient AD by focusing on spatial navigation and orientation deficits, which are increasingly shown to be present in at-risk individuals. Importantly, the navigation system in the brain overlaps substantially with the regions affected by AD in both animal models and humans. Notably, spatial navigation has fewer verbal, cultural and educational biases than current cognitive tests and could enable a more uniform, global approach towards cognitive fingerprints of AD and better cognitive treatment outcome measures in future multicentre trials. The current Review appraises the available evidence for spatial navigation and/or orientation deficits in preclinical, prodromal and confirmed AD and identifies research gaps and future research priorities

Perception of self-motion & regulation of walking speed in older adults in comparison to young adults

Older adults display slower walking speeds, which could be attributed to an altered perception of optic flow (OF) speed. It has been previously demonstrated that older adults exhibit altered speed discriminations when exposed to expanding OFs. Whether these perceptual impairments explain slower and less context-adapted gait speeds in older adults remains unknown. The purpose of this study was to contrast speed discrimination thresholds and gait speed adaptations in young-old vs. younger adults. I also sought to determine whether speed discrimination and walking speed modulation abilities were related in older adults. Twelve young adults (23.0 ± 2.4 years) and twelve young-old adults (68.8 ± 4.4 years) participated in a speed discrimination experiment and two walking experiments. In the speed discrimination experiment, participants wore a head-mounted display (HMD) that displayed a virtual reality (VR) scenario depicting self-motion along a corridor. Participants were asked to choose which of two scenes that were played sequentially, moved faster. Speed discrimination thresholds were determined as the geometric mean of the last eight reversals. In the walking tasks, participants walked on a self-paced treadmill while wearing the HMD and viewing the VR scene showing OF speeds ranging from 0.25 to 2 times their comfortable speed. In the first walking paradigm, participants were instructed to walk the corridor distance of each test trial, which displayed different OF speeds, within the same time as during a preceding control trial that presented an OF matching their comfortable gait speed. In the second walking paradigm, participants were instructed to match their gait speed to the speed of the OF shown in the virtual environment. Walking speed modulation was measured as the slope between walking speed changes and OF speed changes (walking paradigm 1), and as the absolute error in walking speed with respect to the target speed (walking paradigm 2). Older adults showed larger speed discrimination thresholds, more attenuated slopes and larger errors in speed compared to their younger counterpart. Within the older group, speed discrimination thresholds were not significantly related to speed modulation abilities, as measured by the slopes and absolute errors in speed. These findings indicate that older age affects both the ability to perceive speed information from OF and to modulate walking speed in response to OF speed changes. It is suggested that poor visual motion perception may be one of the contributing factors leading to a mobility decline in older adults.Les gens âgés ont une démarche plus lente, ce qui peut être attribué à une perception fautive de la vitesse du flux optique (FO). Il a déjà été démontré que les personnes âgées ont une capacité altérée à discriminer la vitesse de stimuli visuels décrivant des FO à différentes vitesses. On ne sait toujours pas si cette perception déficiente explique que leur vitesse de marche soit plus lente et que leur démarche soit moins adaptée aux demandes contextuelles. Le but de cette étude était de comparer le seuil de discrimination de la vitesse et l'adaptation de la vitesse de marche chez des jeunes personnes et des personnes âgées en bonne santé. J'ai aussi examiné la relation entre la perception de la vitesse et l'habilité à contrôler la vitesse de marche. Douze jeunes adultes (23.0 ± 2.4 ans) et douze adultes plus âgées (68.8 ± 4.4 ans) ont participé à une évaluation de la perception de la vitesse et à deux évaluations de la démarche. Lors de l'expérience de perception de la vitesse, les participants étaient en position assise et portaient un casque de réalité virtuelle illustrant leur déplacement le long d'un corridor à différentes vitesses. Ensuite, les participants devaient identifier laquelle des deux scènes présentées était la plus rapide. Les seuils de perception de la vitesse ont été mesurés par la moyenne géométrique des huit derniers changements de vitesse. Lors des tâches de marche, les participants marchaient sur un tapis roulant auto-rythmé en portant un casque de réalité virtuelle montrant des scènes présentées à des vitesses de FO variant de 0,25 à 2 fois leur vitesse de marche confortable. Lors du premier test de marche, les participants devaient marcher la longueur du corridor qui décrivaient des vitesses variées de FO (condition expérimentale) et ce, durant la même période de temps qu'un essai précédent illustrant un FO équivalant à leur vitesse confortable de marche (condition contrôle). Lors de la deuxième session, on a demandé aux participants de marcher à une vitesse équivalente à la vitesse du FO présentée dans l'environnement virtuel. La modulation de la vitesse de marche a été mesurée selon la pente entre les changements de vitesse de marche et les changements de vitesses du FO (premier test de marche) et avec les erreurs absolues de vitesse de marche par rapport à la vitesse cible (deuxième test de marche). Les adultes plus âgés ont démontré des seuils plus élevés de discrimination des vitesses, des pentes plus atténuées et de plus grandes marges d'erreurs de vitesse lorsque comparés aux jeunes adultes. Parmi le groupe plus âgé, les seuils de discrimination des vitesses n'étaient pas reliés de façon significative aux habiletés à moduler la vitesse de marche, tel que mesurés par les pentes et les erreurs de vitesse. Ces résultats indiquent que le vieillissement affecte autant l'habileté à percevoir les vitesses du FO que celle à moduler sa vitesse de marche en réponse aux changements de vitesse de FO. Ces observations suggèrent qu'une mauvaise perception de mouvements visuels pourrait être un des facteurs contribuant au déclin de la mobilité chez les personnes âgées

Mindfulness-Based Therapies in the Treatment of Functional Gastrointestinal Disorders: A Meta-Analysis

Background. Functional gastrointestinal disorders are highly prevalent and standard treatments are often unsatisfactory. Mindfulness-based therapy has shown benefit in conditions including chronic pain, mood, and somatization disorders. Objectives. To assess the quality and effectiveness reported in existing literature, we conducted a meta-analysis of mindfulness-based therapy in functional gastrointestinal disorders. Methods. Pubmed, EBSCO, and Cochrane databases were searched from inception to May 2014. Study inclusion criteria included randomized, controlled studies of adults using mindfulness-based therapy in the treatment of functional gastrointestinal disorders. Study quality was evaluated using the Cochrane risk of bias. Effect sizes were calculated and pooled to achieve a summary effect for the intervention on symptom severity and quality of life. Results. Of 119 records, eight articles, describing seven studies, met inclusion criteria. In six studies, significant improvements were achieved or maintained at the end of intervention or follow-up time points. The studies had an unclear or high risk of bias. Pooled effects were statistically significant for IBS severity (0.59, 95% CI 0.33 to 0.86) and quality of life (0.56, 95% CI 0.47 to 0.79). Conclusion. Studies suggest that mindfulness based interventions may provide benefit in functional gastrointestinal disorders; however, substantial improvements in methodological quality and reporting are needed