Combined functional MRI and diffusion tensor imaging analysis of visual motion pathways.
BACKGROUND
Motion perception may be preserved after damage to striate cortex (primary visual cortex, area V1). Awareness and normal discrimination of fast-moving stimuli have been observed even in the complete absence of V1. These facts suggest that motion-sensitive cortex (the V5/MT complex or V5/MT+) may be activated by direct thalamic or collicular inputs that bypass V1. Such projections have been identified previously in monkeys but have not been shown in humans using neuroimaging techniques.


METHODS
We used diffusion tensor imaging (DTI) tractography to visualize white matter fiber tracts connecting with V5/MT+ in 10 healthy volunteers. V5/MT+ was localized for each subject using functional MRI (fMRI). Functional activity maps were overlaid on high-resolution anatomical images and registered with the diffusion-weighted images to define V5/MT+ as the region of interest (ROI) for DTI tractography analysis. Fibers connecting to V1 were excluded from the analysis.


RESULTS
Using conservative tractography parameters, we found connections between the V5/MT+ region and the posterior thalamus and/or superior colliculus in 4 of 10 subjects.


CONCLUSIONS
Connections between the V5/MT+ region and the posterior thalamus and/or superior colliculus may explain visual motion awareness in the absence of a functioning V1.
Lanyon
Linda J
LJ
Human Vision and Eye Movement Laboratory, University of British Columbia, Vancouver, British Columbia, Canada. llanyon@eyecarecentre.org
Giaschi
Deborah
D
Young
Simon Au
SA
Fitzpatrick
Kevin
K
Diao
Lu
L
Bjornson
Bruce H
BH
Barton
Jason J S
JJ
D000328:Adult; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D013477:Superior Colliculi / Q000098:blood supply / Q000502:physiology; D013788:Thalamus / Q000098:blood supply / Q000502:physiology; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology*; D014795:Visual Pathways / Q000098:blood supply* / Q000502:physiology*; D055815:Young Adult
D010100:Oxygen