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William Brixius, Jessica Green; Modality independent recruitment in the occipital lobe: A meta-analysis of early-blind and sighted fMRI and PET studies. . Journal of Vision 2016;16(12):139. https://doi.org/10.1167/16.12.139.
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Occipital cortex is classically considered vision-specific, with the exception that visual loss results in recruitment for non-visual tasks. However, crossmodal and multisensory processing research suggests that occipital activity is modulated by non-visual inputs, particularly when vision is degraded or temporarily limited. One possibility is that occipital regions receive inputs from multiple sensory modalities (vision, audition, touch), with vision the most informative for tasks recruiting occipital areas, therefore dominating occipital processing. Thus, when visual input is removed, non-visual occipital responses can be "unmasked". To investigate occipital recruitment by non-visual stimuli, we conducted activation likelihood estimation meta-analyses on fMRI and PET studies reporting early-blind and sighted participant neural activations for auditory and tactile tasks. Analysis of early-blind>sighted contrasts revealed an early-blind activation network comprising bilateral cuneus, lingual and inferior occipital gyri, and right-lateralized middle occipital and inferior temporal gyri. These results support the notion that similar occipital areas are recruited in the early-blind for non-visual spatial information as those recruited in sighted participants during visual tasks. In a second analysis, we examined auditory and haptic task>rest and task>task coordinates reported for early-blind participants and sighted participants with temporarily restricted vision. The conjunction of early-blind and sighted participant activity revealed common activation in bilateral cuneus and inferior parietal lobule, right lingual, postcentral, and superior/inferior temporal gyri, and left insula, middle temporal, and medial frontal gyri. The consistent inclusion of lingual gyrus and cuneus across modalities suggests that auditory and somatosensory modalities can recruit occipital cortex for non-visual processing, even in sighted individuals. The similarity of the recruited areas in sighted individuals and those whose vision was lost early in life further suggests that occipital cortex may be organized for specific functions (e.g., spatial localization, object identification, motion processing) in all modalities, but that these tasks are most easily accomplished using visual input.
Meeting abstract presented at VSS 2016
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