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Abnormal functional connectivity between ipsilesional V5/MT+ and contralesional striate cortex (V1) in blindsight
Juha Silvanto1, Vincent Walsh, Alan Cowey
1Department of Psychology, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK. juha@essex.ac.uk
Experimental Brain Research
|February 10, 2009
Summary
Transcranial magnetic stimulation revealed abnormal functional connections in a blindsight patient. These findings suggest altered pathways between visual areas V5/MT+ and early visual cortex following brain damage.
Area of Science:
- Neuroscience
- Visual Neuroscience
- Cognitive Neuroscience
Background:
- Unilateral lesions to the primary visual cortex (V1) can induce reorganization of anatomical pathways in the visual system.
- Abnormal pathways, including connections between the lateral geniculate nucleus and extrastriate cortex, and enhanced callosal connections, have been observed in individuals with V1 damage.
Observation:
- This study utilized transcranial magnetic stimulation (TMS) to investigate the functional significance of these abnormal pathways in a well-documented blindsight subject (GY).
- TMS was applied over the motion-sensitive area V5/MT+ in GY's damaged hemisphere.
Findings:
- In the blindsight subject GY, TMS over V5/MT+ modulated phosphene appearance induced from V1 in the undamaged hemisphere.
- In contrast, TMS over V5/MT+ did not affect V1-induced phosphenes in control subjects, indicating abnormal functional connectivity.
Implications:
- The results demonstrate a functional link between V5/MT+ in the damaged hemisphere and the early visual cortex in the undamaged hemisphere.
- This functional abnormality is consistent with previously identified abnormal anatomical connectivity in GY.
- The study highlights the utility of TMS in probing functional connectivity in cases of visual cortex damage and blindsight.
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