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SPATIAL RELATIONSHIPS BETWEEN RETINOTOPY AND FOUR
OTHER FEATURE MAPS IN FERRET VISUAL CORTEX.
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| In the primary visual cortex, spatial relationships between
some combinations of stimulus feature maps have been described, while others
are less well understood. In particular, how retinotopy, one of the most
fundamental features mapped, relates to other maps has remained elusive.
Using optical imaging of intrinsic signals, we have analyzed spatial relationships
between functional maps of retinotopy, orientation, ocular dominance, spatial
frequency, and direction. We find that the magnification factor of visual
space is anisotropic in ferret primary visual cortex. Specifically, the
representation of visual space is more compressed along the azimuth axis
than along the elevation axis. This distorted magnification factor appears
to be reflected in the orientation map: orientation fracture lines have
a significant tendency to lie along the low magnification axis of retinotopy.
Furthermore, orientation and retinotopic gradient angles tend to be orthogonal.
These relationships suggest that along the axis where receptive field location
changes more slowly, orientation changes more rapidly. Similarly, we find
that high rate-of-change regions in the orientation map colocalize with
low rate-of-change regions of ocular dominance and spatial frequency maps.
However, most direction fracture lines overlap with high rate-of-change
regions of the orientation map, except for some which bisect iso-orientation
domains. The preferred direction of motion is orthogonal to the preferred
orientation over most of cortex. It appears that the spatial layouts of
each of these five functional maps, including the retinotopic map, are highly
interdependent. Supported by: NIH grant EY07023. |