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Abstract:
The presence of focal lesions in primary visual cortex (V1) provides the opportunity to study the role of
extra-geniculo-striate pathways for activating extra-striate visual cortex. Previous studies in the macaque have
shown that cells in area V2 stop firing after reversibly cooling V1 (Girard and Bullier, 1989; Schiller et al.,
1974). However no studies on long term recovery after V1 lesions have been reported in the macaque. Here
we use fMRI of the macaque monkey brain to study the organization of V2 from baseline levels up to 16
months post-lesioning. We find that BOLD responses in the lesion projection zone (LPZ) of area V2 are
reduced by 80 compared to pre-lesion levels. Surprisingly the retinotopic organization inside the area V2
LPZ is similar before and after inducing the V1 lesion, suggesting that V2 activation is not the result of input
arising from nearby non-lesioned V1 cortex. Monitoring of the activity over time after the lesion did not
reveal systematic changes in signal amplitude near the LPZ border. We conclude that visually driven
activation of extra-striate area V2 as revealed by the BOLD signal is 1) significantly reduced, but still present
after depriving it of V1 input, 2) the area V2 LPZ largely retains its original retinotopic organization, and 3)
the strength of visual modulation inside the LPZ does not seem to increase significantly up to 16 months
post-lesioning. We discuss our findings in the context of parallel pathways in the brain which can activate V2
in the absence of V1 input and may contribute to the behavioral phenomenon of blindsight.
