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Human blindsight is mediated by an intact geniculo-extrastriate pathway
Sara Ajina1,2, Franco Pestilli3, Ariel Rokem4,5
1Oxford Centre for Functional MRI of the Brain, University of Oxford, Oxford, United Kingdom.
Elife
|October 21, 2015
Summary
Blindsight, or residual vision after primary visual cortex damage, may rely on the geniculo-hMT+ pathway. This white-matter tract is intact in blindsight-positive patients but impaired in those without residual vision.
Area of Science:
- Neuroscience
- Vision Science
- Neuroimaging
Background:
- Damage to the primary visual cortex (V1) can cause hemianopia, a condition characterized by vision loss in half of the visual field.
- Despite V1 damage, some patients exhibit blindsight, retaining partial visual capabilities.
- The neural underpinnings of blindsight are not fully understood, with several white-matter pathways proposed.
Purpose of the Study:
- To investigate the role of specific white-matter pathways in facilitating blindsight in patients with V1 damage.
- To determine if the integrity of the geniculo-hMT+ pathway correlates with the presence of blindsight.
Main Methods:
- Visual psychophysics was used to assess residual vision in patients.
- Diffusion-weighted magnetic resonance imaging (dMRI) and fibre tractography were employed to analyze white-matter pathways.
- Seventeen adult patients with V1 damage and nine age-matched controls participated.
Main Results:
- All blindsight-positive individuals demonstrated intact geniculo-hMT+ pathways.
- Blindsight-negative individuals showed significantly impaired or unmeasurable geniculo-hMT+ pathways.
- Other previously implicated pathways (superior colliculus to hMT+, inter-hMT+ connections) were not consistently present in blindsight-positive cases.
Conclusions:
- The integrity of the white-matter pathway connecting the lateral geniculate nucleus to the motion area hMT+ is crucial for blindsight.
- These findings highlight the geniculo-hMT+ pathway as a key substrate for residual vision after V1 damage.
- Understanding these pathways can inform the development of rehabilitation strategies for hemianopia.
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