Biology subjects

van Hoof, R.

Publications and source records attributed to van Hoof, R..

4 recordsLinked to original sources

bioRxiv2026

Early Vision Shapes Recurrent Processing in the Human Visual Cortex

Recurrent processing involves feedforward, feedback and lateral connections and is thought to allow efficient visual processing. Anatomical and behavioral studies in humans have suggested that feedback connections mature later in development than feedforward connections and thus were proposed to depend to a larger degree on experience. In order to isolate feedforward from feedback activity and to investigate the role of early visual experience, we assessed seven individuals with reversed congenital cataracts and nine sighted controls using an "occlusion paradigm" with 7T magnetic resonance imaging (Smith & Muckli, 2010): Grayscale images of scenes were presented with the lower right quadrant covered by a white rectangle. We examined whether information about category (beaches, buildings, highways) and individual scenes could be extracted from early visual region vertices (V1 - V3) associated with the occluded quadrant of the visual field, in the absence of bottom-up visual input. This was achieved by decoding individual category or scene context utilizing a linear support vector machine. In addition, bidirectional information flow was assessed using connective field modeling. While both groups showed successful decoding of scene and category from vertices receiving bottom-up visual input, the accuracy was higher in normally sighted individuals than in individuals with reversed congenital cataracts. When bottom-up input was removed, decoding of categories remained successful in both groups, but decoding of individual scenes was only possible in normally sighted control individuals. Connective field modeling results indicated a less precise alignment of feedforward and feedback processing during visual stimulation in individuals with reversed congenital cataracts. These findings suggest that early visual experience is crucial for the refinement of feedback activity which in turn is crucial for well-tuned feedforward processing.

neuroscience↗

bioRxiv2024

Optimal placement of high-channel visual prostheses in human retinotopic visual cortex

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSObjectiveC_ST_ABSRecent strides in neurotechnology show potential to restore vision in individuals afflicted with blindness due to early visual pathway damage. As neuroprostheses mature and become available to a larger population, manual placement and evaluation of electrode designs becomes costly and impractical. An automatic method to optimize the implantation process of electrode arrays at large-scale is currently lacking. ApproachHere, we present a comprehensive method to automatically optimize electrode placement for visual prostheses, with the objective of matching pre-defined phosphene distributions. Our approach makes use of retinotopic predictions combined with individual anatomy data to minimize discrepancies between simulated and target phosphene patterns. While demonstrated with a 1000-channel 3D electrode array in V1, our pipeline is versatile, potentially accommodating any electrode design and allowing for design evaluation. Main resultsNotably, our results show that individually optimized placements in 362 brain hemi-spheres outperform average brain solutions, underscoring the significance of anatomical specificity. We further show how virtual implantation of multiple individual brains highlights the challenges of achieving full visual field coverage owing to single electrode constraints, which may be overcome by introducing multiple arrays of electrodes. Including additional surgical considerations, such as intracranial vasculature, in future iterations could refine the optimization process. SignificanceOur open-source software streamlines the refinement of surgical procedures and facilitates simulation studies, offering a realistic exploration of electrode configuration possibilities.

neuroscience↗

bioRxiv2020

A probabilistic functional parcellation of human occipito-temporal cortex

Human visual cortex contains many retinotopic and category-specific regions. These brain regions have been the focus of a large body of functional MRI research, significantly expanding our understanding of visual processing. As studying these regions requires accurate localization of their cortical location, researchers perform functional localizer scans to identify these regions in each individual. However, it not always possible to conduct these localizer scans. Here, we developed and validated a functional region of interest atlas of early visual and category-selective regions in human ventral and lateral occipito-temporal cortex. Results show that for the majority of fROIs, cortex-based alignment results in lower between-subject variability compared to nonlinear volumetric alignment. Furthermore, we demonstrate that (1) the atlas accurately predicts the location of an independent dataset of ventral temporal cortex ROIs and other atlases of place-selectivity, motion-selectivity, and retinotopy. Next, (2) we show that the majority of voxel within our atlas are responding mostly to the labelled category in a left-out subject cross-validation, demonstrating the utility of this atlas. The functional atlas is publicly available (download.brainvoyager.com/data/visfAtlas.zip) and can help identify the location of these regions in healthy subjects as well as populations (e.g. blind people, infants) in which functional localizers cannot be run.

neuroscience↗

bioRxiv2019

Active head motion reduction in Magnetic Resonance Imaging using tactile feedback

Head motion is a common problem in clinical as well as empirical (functional) Magnetic Resonance Imaging applications, as it can lead to severe artefacts that reduce image quality. The scanned individuals themselves, however, are often not aware of their head motion. The current study explored whether providing subjects with this information using tactile feedback would reduce their head motion and consequently improve image quality. In a single session that included six runs, 24 participants performed three different cognitive tasks: (1) passive viewing, (2) mental imagery, and (3) speeded responses. These tasks occurred in two different conditions: (a) with a strip of medical tape applied from one side of the MR head-coil, via the participants forehead, to the other side, and (b) without the medical tape being applied. Results revealed that application of medical tape to the forehead of subjects to provide tactile feedback significantly reduced both translational as well as rotational head motion. While this effect did not differ between the three cognitive tasks, there was a negative quadratic relationship between head motion with and without feedback. That is, the more head motion a subject produced without feedback, the stronger the motion reduction given the feedback. In conclusion, the here tested method provides a simple and cost-efficient way to reduce subjects head motion, and might be especially beneficial when extensive head motion is expected a priori.

neuroscience↗