Daniel-Robert Chebat

The hippocampus is essential for efficient navigation. Although lack of visual experience from birth induces volumetric and structural modifications to the hippocampus, tactile and auditory navigation remain partially preserved in congenitally blind (CB) individuals. Structural studies in this population have relied on global volume or tail–body–head segmentations, leaving the contributions of individual hippocampal subfields to navigation unresolved. We investigated hippocampal subfield volumes and their association with navigational learning in CB adults compared to sighted controls. Structural MRI data were analyzed using probabilistic cytoarchitectonic ROIs to quantify volumes of Cornu Ammonis (CA), Fascia Dentata (FD), Subiculum (SUB), and the Hippocampal–Amygdaloid Transition Area (HATA). Participants performed obstacle detection and avoidance tasks with a tactile sensory substitution device in a real‐world obstacle course. CB participants showed significant volume reductions in left CA and FD compared to sighted controls after total brain volume correction. Obstacle detection learning was associated with bilateral CA and SUB volumes in sighted controls, whereas in CB participants it was selectively associated with right CA and right HATA volumes. Obstacle avoidance learning showed no robust hippocampal associations in either group. Our results indicate that hippocampal subfield–navigation associations are selective and component‐dependent in the absence of vision, rather than reflecting uniform hippocampal involvement.

Navigation is a fundamental cognitive ability that relies on the hippocampus, a brain region that is known for its role in spatial representation and memory. In individuals with congenital blindness, the absence of visual input leads to significant neuroplastic adaptations that support alternative navigation strategies. This review examines the structural and functional modifications of the hippocampus in individuals who are blind and explores the broader neural mechanisms underlying their spatial abilities. We discuss how cross-modal plasticity repurposes the visual cortex for navigation, the role of sensory substitution devices in facilitating spatial learning, and behavioral performance in navigation tasks. Additionally, we highlight the implications of these findings for assistive technologies and brain-machine interfaces designed to enhance mobility in blind individuals. By synthesizing recent research, this review provides insights into the remarkable adaptability of the brain in response to sensory loss and underscores the importance of understanding neural plasticity for developing effective navigation aids.

In congenital blindness (CB), tactile and auditory information can be reinterpreted by the brain to compensate for visual information through brain plasticity mechanisms triggered by training

Deductive reasoning and working memory are integral parts of executive functioning and are important skills for blind people in everyday life. Despite the importance of these skills, the influence of visual experience on reasoning and working memory skills, as well as on the relationship between these, is unknown. In this study, fifteen participants with congenital blindness (CB), fifteen with late blindness (LB), fifteen sighted blindfolded controls (SbfC), and fifteen sighted participants performed two tasks of deductive reasoning and two of working memory. We found that while the CB and LB participants did not differ in their deductive reasoning abilities, the CB group performed worse than the sighted controls, and the LB group performed better than the SbfC group. Those with CB outperformed all the other groups in both of the working memory tests. Working memory is associated with deductive reasoning in all three visually impaired groups, but not in the sighted group. These findings suggest that deductive reasoning is not a uniform skill, and that it is associated with visual impairment onset, the level of reasoning difficulty, and the degree of working memory load.

Vision loss has dramatic repercussions on the quality of life of affected people, particularly with respect to their orientation and mobility. Many devices are available to help blind people to navigate in their environment. The EyeCane is a recently developed electronic travel aid (ETA) that is inexpensive and easy to use, allowing for the detection of obstacles lying ahead within a 2 m range. The goal of this study was to investigate the potential of the EyeCane as a primary aid for spatial navigation. Three groups of participants were recruited: early blind, late blind, and sighted. They were first trained with the EyeCane and then tested in a life-size obstacle course with four obstacles types: cube, door, post, and step. Subjects were requested to cross the corridor while detecting, identifying, and avoiding the obstacles. Each participant had to perform 12 runs with 12 different obstacles configurations. All participants were able to learn quickly to use the EyeCane and successfully complete all trials. Amongst the various obstacles, the step appeared to prove the hardest to detect and resulted in more collisions. Although the EyeCane was effective for detecting obstacles lying ahead, its downward sensor did not reliably detect those on the ground, rendering downward obstacles more hazardous for navigation.

In congenital blindness (CB), tactile, and auditory information can be reinterpreted by the brain to compensate for visual information through mechanisms of brain plasticity triggered by training. Visual deprivation does not cause a cognitive spatial deficit since blind people are able to acquire spatial knowledge about the environment. However, this spatial competence takes longer to achieve but is eventually reached through training-induced plasticity. Congenitally blind individuals can further improve their spatial skills with the extensive use of sensory substitution devices (SSDs), either visual-to-tactile or visual-to-auditory. Using a combination of functional and anatomical neuroimaging techniques, our recent work has demonstrated the impact of spatial training with both visual to tactile and visual to auditory SSDs on brain plasticity, cortical processing, and the achievement of certain forms of spatial competence. The comparison of performances between CB and sighted people using several different sensory substitution devices in perceptual and sensory-motor tasks uncovered the striking ability of the brain to rewire itself during perceptual learning and to interpret novel sensory information even during adulthood. We discuss here the implications of these findings for helping blind people in navigation tasks and to increase their accessibility to both real and virtual environments.

"Introduction to the Special Issue on Multisensory Space — Perception, Neural Representation and Navigation" published on 17 Mar 2020 by Brill.

Despite the fact that complete visual deprivation leads to volumetric reductions in brain structures associated with spatial learning, blind individuals are still able to navigate. The neural structures involved in this function are not fully understood. Our study aims to correlate the performance of congenitally blind individuals (CB) and blindfolded sighted controls (SC) in a life-size obstacle-course using a visual-to-tactile sensory substitution device, with the size of brain structures (voxel based morphometry-VBM-) measured through structural magnetic resonance Imaging (MRI). VBM was used to extract grey matter volumes within several a-priori defined brain regions in all participants. Principal component analysis was utilized to group brain regions in factors and orthogonalize brain volumes. Regression analyses were then performed to link learning abilities to these factors. We found that (1) both CB and SC were able to learn to detect and avoid obstacles; (2) their learning rates for obstacle detection and avoidance correlated significantly with the volume of brain structures known to be involved in spatial skills. There is a similar relation between regions of the dorsal stream network and avoidance for both SC and CB whereas for detection, SC rely more on medial temporal lobe structures and CB on sensorimotor areas.