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Lindsay Lewis, Melissa Saenz, Ione Fine; Patterns of cross-modal plasticity in the visual cortex of early blind human subjects across a variety of tasks and input modalities. Journal of Vision 2007;7(9):875. doi: https://doi.org/10.1167/7.9.875.
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© ARVO (1962-2015); The Authors (2016-present)
A number of studies have demonstrated cross-modal responses within visual cortex of blind subjects. However, to date, cross-modal plasticity has not been compared across a variety of tasks and modalities. If cross-modal plasticity is driven by anatomical connectivity, similar activations might be expected for a given modality, regardless of task. If cross-modal plasticity is driven by functional role, similar activations might be expected for a given task (mapped onto normal specializations of visual cortex), regardless of modality.
FMRI responses to a variety of tasks were measured in early blind, sighted, and sight recovery subjects. Auditory tasks included frequency, motion, and letter trigram discrimination. Tactile tasks included orientation, letter trigram, and plastic animal discrimination. In sighted and sight recovery subjects, visual tasks included orientation, letter trigram, and animal picture discrimination, as well as a motion stimulus. Data were collected with a GLM design using a sparse pulse sequence. Sight recovery and tactile data are still being analyzed.
In blind but not in sighted subjects, cross-modal responses were found within MT+ across all auditory tasks. This general response to auditory stimuli within MT+ suggests that in visually deprived subjects an anatomical route between MT+ and auditory areas may exist. However, MT+ responses were stronger for the auditory motion (see also Saenz et al. VSS 2007) and letter task than for the frequency task, with a lateralization asymmetry between the two tasks (motion: right dominance, letters: left dominance), suggesting that functional demands also modulate cross-modal plasticity. In addition to MT+, the auditory letter task also activated left fusiform areas. In sighted subjects, comparable areas within left fusiform and MT+ were activated by the visual letter task. This selective cross-modal response to auditory letters within left fusiform areas is therefore likely to be primarily driven by functional demands.
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