| Abstract No.: | A-D1130 |
| Country: | Canada |
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| Title: | SURROUND SUPPRESSION MAPS IN THE PRIMARY VISUAL CORTEX REVEALED BY OPTICAL BRAIN IMAGING. |
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| Authors/Affiliations: | 1 Matthieu Vanni, 1 Christian Casanova
1 Ecole d'Optometrie de Montreal, QC, Canada |
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| Content: | Objectives: Responses of cells in the primary visual cortex depend on stimulus size. Discharge levels increase and reach a maximum for a stimulus size equal to the classical receptive field (cRF). Thereafter, the response may either reach a plateau or decrease in an asymptotic way as the stimulus extends beyond the cRF. While the stimulus-size dependency has been well documented at the cellular level, nothing is known about its consequences on global functional maps.
Materials and Methods: Optical imaging of intrinsic signals (OIS) in the primary visual cortex was carried out in 11 anesthetized cats. Orientation map were performed for different stimulus diameters (3 to 40 deg, and a full screen condition).
Results: The spread of activation for small stimulations (less than 6 deg) was around 10 to 30 mm2. The pixelwise measure of the signal magnitude in this area showed a modular organisation: Half of the pixels had a maximum activation for the full screen stimulation (full field facilitation) and the other half attained their maximum for diameters around 16 deg in area 17 and 24 deg in area 18. For these full field suppressions the optimal size of this area increased with the stimulus elevation in the visual field and the suppression by the full screen stimulation was between 30 to 40 % in both areas. This pattern seems to be an organized map, constant in time, uncorrelated with the orientation map.
Conclusion: Thus, the maximum activation revealed by OIS necessitates the stimulation of a much larger spatial area than that observed with single cells. This difference is likely due to the fact that OIS reflects in- and out going signals and reveals activity of adjacent neurons being part of intra-cortical and thalamo-cortical circuits. Supp. NSERC and CIHR to CC |
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