Article Information

• PDF (711 kb)

PubMed

• Articles by P.C. Jordan

Related Articles

• Visual cortex: Looking into a Klein bottle

  Visual cortex: Looking into a Klein bottle Current Biology, Volume 6, Issue 7, 1 July 1996, Pages 776-779 Nicholas V Swindale Summary Arguments based on mathematical topology may help in understanding the organization of topographic maps in the cerebral cortex. Summary | Full Text | PDF (289 kb)

• Orientation Preference Patterns in Mammalian Visual Cortex

  Orientation Preference Patterns in Mammalian Visual Cortex Neuron, Volume 29, Issue 2, 1 February 2001, Pages 519-527 Alexei A. Koulakov and Dmitri B. Chklovskii Summary In the visual cortex of many mammals, orientation preference changes smoothly along the cortical surface, with the exception of singularities such as pinwheels and fractures. The reason for the existence of these singularities has remained elusive, suggesting that they are developmental artifacts. We show that singularities reduce the length of intracortical neuronal connections for some connection rules. Therefore, pinwheels and fractures could be evolutionary adaptations keeping cortical volume to a minimum. Wire length minimization approach suggests that interspecies differences in orientation preference maps reflect differences in intracortical neuronal circuits, thus leading to experimentally testable predictions. We discuss application of our model to direction preference maps. Summary | Full Text | PDF (1100 kb)

• Relationship between the Ocular Dominance and Orientation Ma...

  Relationship between the Ocular Dominance and Orientation Maps in Visual Cortex of Monocularly Deprived Cats Neuron, Volume 19, Issue 2, 1 August 1997, Pages 307-318 Michael C Crair, Edward S Ruthazer, Deda C Gillespie and Michael P Stryker Summary The significance of functional maps for cortical plasticity was investigated by imaging of intrinsic optical signals together with single-unit recording in kittens. After even a brief period of monocular deprivation during the height of the critical period, only isolated patches of visual cortex continued to respond strongly to the closed eye. These deprived-eye patches were located on the pinwheel center singularities of the orientation map and consisted of neurons that were poorly selective for stimulus orientation. Neurons in regions surrounding the deprived-eye patches responded only weakly to the deprived eye but were well tuned for the same stimulus orientation that optimally excited them when presented to the open, nondeprived eye. The coincidence of deprived-eye patches with pinwheel center singularities, and the selective loss of orientation tuning within the deprived-eye patches, indicate that the orientation and ocular dominance maps are functionally linked and provide compelling evidence that pinwheel center singularities are important for cortical plasticity. Summary | Full Text | PDF (930 kb)

• …more

Abstract

This paper presents calculations of the image potential for an ion in an aqueous pore through lipid membrane and the electric field produced in such a pore when a transmembrane potential is applied. The method used is one introduced by Levitt (1978, Biophys. J. 22:209), who solved an equivalent problem, in which a surface charge density is placed at the dielectric boundary. It is shown that there are singularities in this surface charge density if the model system has sharp corners. Numerically accurate calculations require exact treatment of these singularities. The major result of this paper is the development of a projection method that explicitly accounts for this behavior. It is shown how this technique can be used to compute, both reliably and efficiently, the electrical potential within a model pore in response to any electrical source. As the length of a channel with fixed radius is increased, the peak in the image potential approaches that of an infinitely long channel more rapidly than previously believed. When a transmembrane potential is applied the electric field within a pore is constant over most of its length. Unless the channel is much longer than its radius, the field extends well into the aqueous domain. For sufficiently dissimilar dielectrics the calculated values for the peak in the image potential and for the field well within the pore can be summarized by simple empirical expressions that are accurate to within 5%.