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OPTICAL IMAGING OF INTRINSIC SIGNALS REVEALS VISUAL ORGANIZATION IN MOUSE V1 AND V2.

Dept. of Brain & Cognitive Sci. and the Picower Ctr. for Learning & Memory, MIT, Cambridge, MA, USA

Examining the detailed organization of mouse primary visual cortex (V1) and secondary visual cortex (V2) is important for identifying the role of activity in shaping maps and modules. We used optical imaging of intrinsic signals to examine the retinotopy and possible modular organization of V1 and V2. Adult mice (

2 months old) were anesthetized with a combination of urethane (1.5g/kg) and the sedative chlorprothixene (0.2mg). The skull was thinned over the visual cortex and illuminated with 605 nm light. Visual field elevation and azimuth were mapped by presenting binocularly a single high-contrast bar drifting in periodic fashion. Ocular dominance regions were explored by presenting either periodic drifting bars or drifting gratings of various orientations to the ipsilateral or contralateral eye in interleaved monocular trials. Orientation domains were examined by presenting periodic drifting bars or gratings of various orientations binocularly. Images in response to drifting bars were analyzed by extracting the Fourier component of the intrinsic signal at the periodicity of the drifting bar. Confirming previous work, we find that the vertical meridian lies along the V1/V2 border, and that there is an anisotropy of representation in the elevation axis. Specifically, the cortical magnification factor is approximately 2x greater along the elevation axis relative to the azimuth axis. Similar to higher mammals, this may suggest the presence of finer ocular dominance slabs that tend to run into the V1/V2 border and distort retinotopy by representing the same location in visual space separately for each eye. Compared to a stimulus consisting of drifting gratings, the presentation of a periodic single bar provides a better signal to noise ratio, and may help resolve whether or not modular organizations for ocular dominance and orientation exist in mouse V1 and V2.
Support Contributed By: EY13900 (JRN), EY11512 and NS39022 (MS)

Citation:
J.R. Newton, J. Sharma, H. Yu, M. Sur. OPTICAL IMAGING OF INTRINSIC SIGNALS REVEALS VISUAL ORGANIZATION IN MOUSE V1 AND V2. Program No. 266.9. 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2003. Online.