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.
Scientific impact: Amplyopia is a visual development disorder that is not caused by an ocular problem. It is more related to visual analysis and interpretation in a specific area of the brain, the visual cortex MT zone. This article demonstrated for the first time in adults that the brain can compensate erroneous perceptions by the amplyope eye by using other areas than the MT zone for image analysis. This discovery has the potential to facilitate understanding of this neurological disease and the adaptation mechanisms the brain can use in such situations.
Network contribution: The VHRN has provided funding to Casanova and Hess for their multi-center project
* * *
Original abstract
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.