Cortical column design: a link between the maps of preferred orientation and orientation tuning strength?

Abstract

Abstract. We demonstrate that the map of the preferred orientations and the corresponding map of the orientation tuning strengths as measured with optical imaging are not independent, but that band-pass filtering of the preferred orientation map at each location yields a good approximation of the orientation tuning strength. Bandpass filtering is performed by convolving the map of orientation preference with its own autocorrelation function. We suggest an interpretation of the autocorrelation function of the preferred orientations as synaptic coupling function, i.e., synaptic strength as a function of intracortical distance between cortical cells. In developmental models it has been shown previously that a "Mexican hat"-shaped synaptic coupling function (with a shape similar to that of the autocorrelation function) can produce a realistical-looking pattern of preferred orientations. Since optical imaging performs surface averaging, we discuss the possibility that the connection between the two maps is a measurement artifact of optical imaging. Whether this is the case can only be decided by combining electrode penetrations with optical imaging techniques for which we suggest experiments. We present a model for the generation of both maps from a single computational concept. The model is based on inverse Fourier transform of rather simple twodimensional annulus-shaped spectra which will produce a column structure very similar to real data. Thus, our approach shows that the complex appearance of cortical orientation columns has a rather simple description in the Fourier domain. Our theoretical analysis explains why singularities in the cortex do not have vorticities other than ± 1/2, a result which corresponds to recent experimental findings. This study combines the results from several modeling approaches with recently available optical imaging data to construct a model of both aspects (angle and strength) of the cortical orientation column system. This could alter ideas about cortical development if the link between the two maps can be established as a physiological result.

Neural network model for the coordinated formation of orientation preference and orientation selectivity maps

“…Because these quantities remain identical for changes about +180', the developing orientation preference maps also show this symmetry. In particular, +-, ' [34] Finally, the approach is restricted to weak lateral interactions, which is in contrast to biological evidence (in monkeys, each neuron receives about 2300 synapses [28], where at most 300 belong to afFerent fibers [27] discontinuities, and a reduction of orientation selectivity at these discontinuities, is an inherent feature of our network (see, in contrast, [20] [17] also suggests that regions with +1 vortices might exist in area 17. The strongest reduction of orientation selectivity in the present model occurs in +1 centers of the vortices (though also present at other discontinuities).…”

“…As mentioned above, this is due to the strongly decreasing overlap of the eigenstates with the external perturbation in (15). Thus [20], where reduction of orientation selectivity at discontinuities is achieved by explicitly convolving the orientation preference map with an appropriate kernel, the present model contains an inherent mechanism for the coordinated arrangement of orientation preference and orientation selectivity. It suggests a general principle for the coupling of discontinuities in orientation preference maps and dips in orientation selectivity maps, which is also observed in biology [10].…”

“…Other authors use formal orientation preference vectors with doubled polar angles [18,20] in order to account for the 180' symmetry of orientation preference. Thereby, they introduce the 180' symmetry of the experimentally observed +-, ' vortices into their systems.…”