B.J. Farley; M. Sur
1. Dept Brain and Cognitive Sciences, 2. Picower Center for Learning and Memory, MIT, Cambridge, MA, USA

We have explored the complete retinotopic organization of rat visual cortex using optical imaging of intrinsic signals. Long Evans rats were anesthetized with isoflurane gas in a mixture of nitrous oxide and oxygen. Imaging was performed through the dura using a 700 nm filter. As a stimulus, we used a single vertical or horizontal bar that drifted across the visual field periodically, in a direction orthogonal to its orientation. Light reflectance data was continuously captured, and retinotopic maps generated by analyzing the optical response at the frequency of visual stimulation. Using this technique we have generated robust maps of retinotopy in rat visual cortex. Iso-azimuth contours in V1 run nearly parallel to the antero-posterior axis of cortex, whereas iso-elevation contours run obliquely to this axis and extend from antero-lateral to postero-medial cortex. This layout is very similar to that found in the mouse. Near the center of V1, the magnification factor for vertical space is approximately 0.05 mm/deg, while that for horizontal space is 0.03 mm/deg. Our data additionally indicate the existence of multiple visual areas in rat visual cortex, as evidenced by regions outside of V1 displaying retinotopy patterned distinctly from that within V1.
Support Contributed By: NIH grant NS039022