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Melissa Saenz, Lindsay B. Lewis, Alex G. Huth, Ione Fine, Christof Koch; Responses to auditory motion within visual motion area MT+ in early blind and sight recovery subjects. Journal of Vision 2007;7(9):770. doi: 10.1167/7.9.770.
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© ARVO (1962-2015); The Authors (2016-present)
Over the last decade a series of brain imaging studies in humans have demonstrated that the visual cortex of people who become blind early in life responds to a variety of auditory, tactile, and verbal tasks. However, it remains unclear whether these cross-modal responses map onto the normal functional subdivisions of visual cortex found in sighted individuals. Here, using functional magnetic resonance imaging (fMRI), we tested whether visual cortical area MT+, well established for its role in visual motion processing in sighted subjects, is selectively recruited for auditory motion processing in early blind subjects.
We measured BOLD fMRI responses to moving vs. stationary auditory white noise stimuli in seven normally sighted control subjects, five early-blind subjects, and two formerly (early) blind subjects with partial sight recovery (due to corneal stem cell replacement and cataract removal). Auditory motion stimuli were generated by varying inter-aural level differences (ILD) on stereo headphones. A sparse pulse sequence limited interference of MRI scanner noise with auditory stimuli. In the sighted control and sight recovery subjects we also measured responses to moving vs. stationary visual stimuli in order to functionally locate MT+. In early-blind subjects but not in sighted control subjects, we found that MT+ responded significantly to auditory motion. In sight recovery subjects MT+ responded to both auditory and visual motion.
These results show that in early-blind subjects visual area MT+ can maintain enhanced responses to motion, despite receiving input from a novel modality. This suggests an organizational principal behind cortical cross-modal plasticity, whereby reorganization is influenced by the normal functional role of a given region. In sight recovery subjects, we found that responses to auditory motion in visual area MT+ were at least as strong as the responses to visual motion. Thus, cross-modal responses can persist after sight recovery, coexisting with regained visual responses.
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