# Regensburg 2002 – wissenschaftliches Programm

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# SYPH: Physik im Hirn - Physical Approaches to Brain Function

## SYPH 2: Physik im Hirn - Physical Approaches to Brain Function

### SYPH 2.7: Poster

### Donnerstag, 14. März 2002, 15:30–18:00, Poster D

**Symmetries in the development of the visual cortex** — •Matthias Kaschube^{1}, Fred Wolf^{1,2}, and Theo Geisel^{1} — ^{1}Max-Planck-Institut für Strömungsforschung, Göttingen, Germany — ^{2}Racah Institute of Physics and Center for Neural Computation, The Hebrew University, Jerusalem, Israel

In the visual cortex of the brain, neurons specialized for contour detection are arranged in a complex pattern, the orientation map. This map is almost everywhere continuous but contains a large number of point singularities, called pinwheels. Wolf and Geisel predicted that pinwheels must annihilate during the development of the orientation map, if the development is governed by a dynamics constrained by basic symmetries, including isotropy. Here we investigate if the prediction of pinwheel annihilation sensitively depends on the assumption of isotropy. We calculate the initial pinwheel density for a general anisotropic dynamics and demonstrate that it exhibits a lower bound. For small anisotropies this bound deviates continuously from π and is always smaller then π. Using power spectral densities obtained from measured patterns we show that for realistic degrees of anisotropy the predicted initial pinwheel densities are still larger than the experimentally observed final densities. We conclude that pinwheel annihilation must occur even in the case of anisotropic dynamics of orientation maps.