Abnormal cortical processing of pattern motion in amblyopia: evidence from fMRI
Thompson B, Villeneuve MY, Casanova C, Hess RF. Neuroimage. 2012 60(2):1307-15.
Impact scientifique: L’amblyopie est un désordre du développement visuel qui n’est pas causé par un problème oculaire. Il s’agit plutôt d’un problème d’analyse et d’interprétation de l’image dans une zone spécifique du cerveau, la zone MT du cortex visuel. Cet article démontre pour la première fois chez l’adulte que le cerveau peut compenser les perceptions erronées de l’œil amblyope en utilisant d’autres régions que la zone MT pour l’analyse de l’image. Cette découverte a le potentiel de faciliter la compréhension de cette maladie neurologique et les mécanismes adaptatifs du cerveau dans ces situations.
Contribution du Réseau: Le RRSV a accordé une subvention aux chercheurs Christian Casanova et Robert Hess dans le cadre de leurs travaux en collaboration inter-universitaire.
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Résumé original
Converging evidence from human psychophysics and animal neurophysiology indicates that amblyopia is associated with abnormal function of area MT, a motion sensitive region of the extrastriate visual cortex. In this context, the recent finding that amblyopic eyes mediate normal perception of dynamic plaid stimuli was surprising, as neural processing and perception of plaids has been closely linked to MT function. One intriguing potential explanation for this discrepancy is that the amblyopic eye recruits alternative visual brain areas to support plaid perception. This is the hypothesis that we tested. We used functional magnetic resonance imaging (fMRI) to measure the response of the amblyopic visual cortex and thalamus to incoherent and coherent motion of plaid stimuli that were perceived normally by the amblyopic eye. We found a different pattern of responses within the visual cortex when plaids were viewed by amblyopic as opposed to non-amblyopic eyes. The non-amblyopic eyes of amblyopes and control eyes differentially activated the hMT+ complex when viewing incoherent vs. coherent plaid motion, consistent with the notion that this region is centrally involved in plaid perception. However, for amblyopic eye viewing, hMT+ activation did not vary reliably with motion type. In a sub-set of our participants with amblyopia we were able to localize MT and MST within the larger hMT+ complex and found a lack of plaid motion selectivity in both sub-regions. The response of the pulvinar and ventral V3 to plaid stimuli also differed under amblyopic vs. non-amblyopic eye viewing conditions; however the response of these areas did vary according to motion type. These results indicate that while the perception of the plaid stimuli was constant for both amblyopic and non-amblyopic viewing, the network of neural areas that supported this perception was different.