Society for Neuroscience 2007 Press Book Release

Dear Readers,

For the second consecutive year my abstract was selected to be part of the press book release of the prestigious SfN meeting which took place in San Diego (Nov. 3-7th). Here is a copy of the abstract that was released to the media:

Navigation Skills in the Early Blind Using a Tongue Stimulator.

D-R. Chebat, C. Rainville, K. Madsen, O. Paulson, M., Ptito
Univ. Montreal, Montreal, Canada.
Danish research center fo Magnetic Resonance, Hvidovre Hospital, Hvidovre, Denmark

Program Number: 737.24
Session Date-Time:Tuesday Nov., 6, 1:00 PM
WW17

Navigation is a complex behavior involving a multitude of sensory modalities. Vision is an integral component in navigation, providing the traveler with information about the configuration of proximal and distal space as well as updating motion cuess. The hippocampus has been shown to be involved in visual spatial memory in primates and humans. This brain structure comprises cells that respond to locations that are called place cells. Spatial navigation depends, in part, upon place celle actitivuty in teh hippocampus that plays a fundamental role in the interpretation of visual-based information. The hippocampus is subject to plastic changes humans. For example taxi drivers who have had an extensive visual navigational training show an enlarged right hippocampus whereas lesions to this same region impair retrieval and learning of spatial routes. Topographical memory relies on a network of brain regions involving the hippocampus, visual cortex, frontal lobes and parietal regions. Blind individuals from birth, however, are not impaired on a spatial competenmce level or in the formation of novel spatial maps of the environment when using tactile, proprioceptive or auditory cues. We recently showed, using a technique called Voxel-Based Morphometry (VBM) carried out on whole brain magnetic resonance imaging scans (MRI) that born blind people have a reduced right posterior hippocampus . The question therefore arisses on how blind people form spatial maps of their environment?
We first tested the ability of blind subjects to navigate in an obstacle course. Wearing a camera mounted on glasses and the tongue display unit (TDU) grid on the tongue, they were requested to point to the obstacle (detection), and move towards it and negotiate a path around it (avoidance). We shoed that blind subjects had no difficulty to peform teh task besides a structurally atrophied right posterior hippocampus (see 'Chebat et al., 2007a).
We proposed that they probably relied on other brain structures belonging to the neural network involved in topographical memory. We emphasied the use of neural pathways that connect teh parietal and frontal cortices to the occipital lobe because they are enlarged in the blind compared to the sighted. In a virtual maze task where subjects used their tongue to move along a virtual path while in a 3.0T fMRI scanner, we were able to show that route forming in the blind did not deoend upon the hippocampus but rather on cortical areas.
These results are of great interest since tehy show that the tongue is a useful organ to move around in the environment and to do so, it calls on a reorganization of brain connections that involve the frontal and parietal cortices. The applications of the TDU are therfore important since objects in the enviironment can be signaled to teh tongue in any non-vision situations lie darkness. Tests are currently on their way in deep sea divers wearing infra red goggles and tehir ability to use their tongue as a signal detector.

Society for Neuroscience 2006 Press Book

Last year in Atlanta, my abstract for the Society for Neuroscience (SfN) was chosen abstracts to be part of their press book release. Every year SfN choses 700 abstracts out of over 14, 000 to release to the media. Here is a copy of that abstract.

Volumetric analysis of the hippocampus in early blind subjects.

Society for Neuroscience 2006



Press Book Summary by Daniel-Robert Chebat and Maurice Ptito


This preliminary study is part of an ongoing research program concerned with the anatomo-functional re-organization of the brain resulting from sensory deprivation at birth. We report here that the hippocampus, a structure involved in learning and memory, is significantly reduced in volume compared to normal seeing controls. This reduction concerns mainly the posterior part of the right hippocampal formation.

This finding is novel and interesting because it supports the hypothesis that the hippocampus is involved in the formation of spatial visual maps of the environment. Since our subjects have been blind from birth, the posterior part of the hippocampus showed atrophy.

Previous studies carried out on blinds have shown that these subjects are not impaired on a spatial competence level and that they maintain the capacity to form spatial maps of the environment when using tactile or proprioceptive and/or auditory cues. The absence of vision however complicates the encoding of spatial maps due to the lack of readily available spatial information. Extensive navigational training in normal subjects induces plastic changes in the hippocampus. For example, London taxi drivers show a larger posterior hippocampus compared to controls!

This study emphasizes therefore the importance of vision in the development of brain structures and the role of the posterior part of the right hippocampus in navigational skills that involve visual cues. We have recently shown that the visual pathways of born blind subjects are largely atrophied (Schneider, Kupers and Ptito, 2006). The striate and extrastriate visual areas have a reduced volume and both afferent and efferent fibers are altered.

The question arises then on how do blind people move around in their environment and what are the cerebral structures involved? It is known that spatial representation of the environment can be encoded through other sensory cues such as somesthesis, touch, audition and proprioception. These maps are not exclusively carried out by the hippocampus itself but rather in tandem with other cortical regions. The anterior insula/ventrolateral prefrontal cortex (AI/VP) and parietal cortex (PC) are most likely candidates. AI/VP is associated with the coding of auditory cues and spontaneous route planning and PC is involved in the planning of movements through immediate space when no visual cues are available.

Although navigation requires visual cues for the formation of spatial maps that involves the right hippocampal formation, early blinds are still able to build novel spatial maps of the environment when using tactile, proprioceptive and/or auditory cues. We hypothetize therefore that these map formations are carried out outside of the hippocampus and probably involve the parietal cortex.

These results have never been published and to our knowledge nobody has previously shown that blindness leads to the atrophy of the right posterior hippocampus, a brain structure known to be involved in the formation of visual maps.

These data were collected from a rather large sample of blind subjects and seeing controls using a double blind protocol with two types of analysis from magnetic resonance images (MRI) : volumetric analysis through segmentation of the hippocampus and voxel-based morphometry (VBM). Both approaches yielded the same results.

What would be interesting to do next is Tensor Diffusion Imaging to highlight the nature of the connections (white matter) between the hippocampus and the other cortical areas and correlate anatomy and behavior through route learning.