Biology subjects

Sheynikhovich, D.

Publications and source records attributed to Sheynikhovich, D..

6 recordsLinked to original sources

bioRxiv2025

Prediction and updating abilities in motor imagery during the Timed Up and Go task in young and older adults

Aging is associated with declines in sensorimotor and cognitive functions that affect internal motor models, thought to mediate the risk of falls. Motor imagery, an experimental window into internal models, has been studied in aging, but it remains unclear whether age differentially impacts their predictive versus updating components. In this study, younger and older adults completed the Timed Up and Go task along with imagined trials before and after execution, enabling separate assessment of prediction and update accuracy. It was found that older adults exhibited similar or better accuracy during prediction and update, but the accuracy measures were linked with distinct cognitive and sensorimotor factors in the two age groups. These findings suggest that while internal model function is preserved in healthy aging, at least for every-day tasks, it is shaped by different compensatory mechanisms across the lifespan.

neuroscience↗

bioRxiv2023

Age-related disparities in oscillatory dynamics within scene-selective regions during spatial navigation

Position is a key property that allows certain objects in the environment to attain navigational relevance. Symmetrical processing of object position across the horizontal meridian remains an unchallenged assumption of the spatial navigation literature. Nonetheless, a growing body of research reports vertical inhomogeneities in perceptual tasks, and recent evidence points towards a lower visual field preference in healthy aging. Factoring in the vertical position of objects to better apprehend spatial navigation abilities across the lifespan is essential. The occipital place area (OPA), parahippocampal place area (PPA), and medial place area (MPA) are ideal candidates to support the processing of the vertical location of navigational cues. Indeed, they are implicated in scene processing and spatial cognition, functions that may interact with their underlying retinotopic codes. This study aimed to elucidate whether young and older participants adjusted their gaze patterns and EEG activity within scene-selective regions in response to the vertical arrangement of landmarks. A sample of 21 young and 21 older participants completed a desktop-based task requiring them to navigate using objects at different vertical locations. We equipped them with an eye tracker and a high-density EEG cap. We used a fMRI-informed source-reconstruction algorithm to study the OPA, PPA and MPA with high spatial and temporal precision. Older adults exhibited a higher number of errors compared to young adults during reorientation. This age-related decline in accuracy was accompanied by a tendency among older participants to fixate objects in the lower half of the screen. This gaze bias was absent in young participants, who instead adapted their oculomotor behaviour based on the position of navigationally-relevant information. Another primary finding pertains to the differential pattern of theta and beta band activity in the OPA, PPA and RSC for environments that only contained relevant cues in the upper visual field. It thus appears that scene-selective regions process some aspect of the vertical position of information, irrespectively of their inherent retinotopic biases. Moreover, we revealed striking disparities between age groups in beta/gamma band synchronization in all scene-selective regions, indicating compromised top-down attentional mechanisms during spatial navigation in ageing. These age-related disparities in attentional dynamics might account for performance deficits in older participants. This study sheds light on a systematic downward gaze bias and altered attentional dynamics within scene-selective regions during spatial navigation in older age. It also emphasises the importance of considering vertical positioning as a fundamental property of objects within scenes.

neuroscience↗

bioRxiv2023

Foveal drusen increase fixation instability: fixational eye movements as biomarkers for pre-symptomatic AMD

PurposeThis study aims at linking subtle changes of fixational eye movements (FEM) in controls and in patients with foveal drusen using adaptive optics retinal imaging in order to find anatomo-functional markers for pre-symptomatic Age-related Macular Degeneration (AMD). MethodsWe recruited 7 young controls, 4 older controls and 16 presymptomatic AMD patients with foveal drusen from the Silversight Cohort. A high speed research-grade adaptive optics flood illumination ophthalmoscope (AO-FIO) was used for monocular retinal tracking of fixational eye movements. The system allows for sub-arcminute resolution, high-speed and distortion-free imaging of the foveal area. Foveal drusen position and size were documented using gaze-dependent imaging on a clinical-grade AO-FIO. ResultsFEM were measured with high precision (RMS-S2S=0.0015{degrees} on human eyes) and small foveal drusen (median=60{micro}m) were detected with high contrast imaging. Microsaccade amplitude, drift diffusion coefficient and ISOline Area (ISOA) were significantly larger for patients with foveal drusen compared with controls. Among the drusen participants, microsaccade amplitude was correlated to drusen eccentricity from the center of the fovea. ConclusionsA novel high-speed high-precision retinal tracking technique allowed for the characterization of FEM at the microscopic level. Foveal drusen altered fixation stability, resulting in compensatory FEM changes. Particularly, drusen at the foveolar level seemed to have a stronger impact on microsaccade amplitudes and ISOA. The unexpected anatomo-functional link between small foveal drusen and fixation stability opens up a new perspective of detecting oculomotor signatures of eye diseases at the presymptomatic stage.

neuroscience↗

bioRxiv2020

Modulation of spatial cue processing across the lifespan: a geometric polarization of space restores allocentric navigation strategies in children and older adults

The impact of development and healthy aging on spatial cognition has been traditionally attributed to a difficulty in using allocentric strategies and a preference for egocentric ones. An alternative possibility, suggested by our previous works, is that this preference is actually conditioned by the spatial cues (e.g. geometric of landmark cues) present in the environment rather than a strategic choice per se. We tested this prediction by having 79 subjects (children, young and older adults) navigating a Y-maze composed either of landmarks or geometric cues, with an immersive head-mounted display that allows us to record both head and eye movements. Our results show that when the performance is based on landmarks solely, children and older adults exhibit a deficit in using allocentric strategies when compared to young adults. Hence, an inverted U-profile of allocentric strategies was observed across the lifespan. This was not due to a default of attention to the landmarks, as evidenced by analysis of gaze dynamics. When geometric were provided, however, older adults and children used allocentric strategies in the same proportion as young adults. They were, in addition, as efficient and quick to implement the strategy. We thus propose a reinterpretation of the previous data in the literature, whereby reference to geometric cues is the default mode for spatial representations, which is immune to age, whereas spatial representations fail to be anchored on landmarks early in development and later in aging. This new interpretation has the potential to reunify several data from the literature, ranging from spatial cues processing to strategy preference, and including other spatial skills like path integration and route learning.

neuroscience↗

bioRxiv2019

A model of a panoramic visual representation in the dorsal visual pathway: the case of spatial reorientation and memory-based search

While primates are primarily visual animals, how visual information is processed on its way to memory structures and contributes to the generation of visuospatial behaviors is poorly understood. Recent imaging data demonstrate the existence of scene-sensitive areas in the dorsal visual path that are likely to combine visual information from successive egocentric views, while behavioral evidence indicates the memory of surrounding visual space in extraretinal coordinates. The present work focuses on the computational nature of a panoramic representation that is proposed to link visual and mnemonic functions during natural behavior. In a spiking neural network model of the dorsal visual path it is shown how time-integration of spatial views can give rise to such a representation and how it can subsequently be used to perform memory-based spatial reorientation and visual search. More generally, the model predicts a common role of view-based allocentric memory storage in spatial and non-spatial mnemonic behaviors.

animal behavior and cognition↗

bioRxiv2019

Modeling place cells and grid cells in multi-compartment environments: hippocampal-entorhinal loop as a multisensory integration circuit

Hippocampal place cells and entorhinal grid cells are thought to form a representation of space by integrating internal and external sensory cues. Experimental studies show that different subsets of place cells are controlled by vision, self-motion or a combination of both. Moreover, recent studies in environments with a high degree of visual aliasing suggest that a continuous interaction between place cells and grid cells can result in a deformation of hexagonal grids or in a progressive loss of visual cue control. The computational nature of such a bidirectional interaction remains unclear. In this work we present a neural network model of a dynamic loop between place cells and grid cells. The model is tested in two recent experimental paradigms involving double-room environments that provide conflicting evidence about visual cue control over self-motion-based spatial codes. Analysis of the model behavior in the two experiments suggests that the strength of hippocampal-entorhinal dynamical loop is the key parameter governing differential cue control in multi-compartment environments. Construction of spatial representations in visually identical environments requires weak visual cue control, while synaptic plasticity is regulated by the mismatch between visual- and self-motion representations. More gener-ally our results suggest a functional segregation between plastic and dynamic processes in hippocampal processing.

animal behavior and cognition↗