Hemifield columns co-opt ocular dominance column structure in human achiasma

Area of Science:

• Neuroscience
• Visual Neuroscience
• Neuroimaging

Background:

• The optic chiasm typically routes visual information, crossing inputs from nasal retina to the contralateral hemisphere.
• In achiasmia, the optic chiasm is absent, leading to unusual visual pathway organization.
• Overlapping visual hemifield representations in primary visual cortex (V1) in achiasmia raise questions about visual processing clarity.

Purpose of the Study:

• To investigate the spatial organization of visual hemifield representations in the primary visual cortex (V1) of an achiasmic individual.
• To test the hypothesis that interdigitated representations of nasal and temporal retinal inputs explain vision in achiasmia.
• To compare this organization to ocular dominance columns in neurotypical subjects.

Main Methods:

• High-resolution functional magnetic resonance imaging (fMRI) at 7 Tesla was employed.
• Responses to left and right visual hemifield stimulation were measured in one achiasmic subject using T2-weighted 2D Spin Echo images at 0.8mm isotropic resolution.
• A general linear model analyzed voxel preference for hemifield stimulation during a demanding visual task.

Main Results:

• Interdigitated clusters of voxels preferring left and right hemifield stimulation were observed in the right hemisphere's V1.
• This spatial distribution was stable across two testing days.
• The scale of these interdigitated representations was comparable to human ocular dominance columns.

Conclusions:

• This study provides the first in vivo evidence of interdigitating visual hemifield representations in the V1 of an achiasmic individual.
• This organization likely underlies clear vision in the absence of the optic chiasm.
• The developmental trajectory may parallel that of ocular dominance columns in typical visual systems.