title: Pinwheel-dipole configuration in cat early visual cortex.
abstract: In the early visual cortex, information is processed within functional maps whose layouts are thought to underlie visual perception. However, the precise organization of these functional maps as well as their interrelationships remain unsettled. Here, we show that spatial frequency representation in cat early visual cortex exhibits singularities around which the map organizes like an electric dipole potential. These singularities are precisely co-located with singularities of the orientation map: the pinwheel centers. To show this, we used high resolution intrinsic optical imaging in cat areas 17 and 18. First, we show that a majority of pinwheel centers exhibit in their neighborhood both semi-global maximum and minimum in the spatial frequency map (i.e. extreme values of the spatial frequency in a hypercolumn). This contradicts pioneering studies suggesting that pinwheel centers are placed at the locus of a single spatial frequency extremum. Based on an analogy with electromagnetism, we proposed a mathematical model for a dipolar structure, accurately fitting optical imaging data. We conclude that a majority of orientation pinwheel centers form spatial frequency dipoles in cat early visual cortex. Given the functional specificities of neurons at singularities in the visual cortex, it is argued that the dipolar organization of spatial frequency around pinwheel centers could be fundamental for visual processing.
authors.affiliation: Mathematical Neuroscience Team, CIRB - Collège de France (CNRS UMR 7241, INSERM U1050, UPMC ED 158, MEMOLIFE PSL), 11 Place Marcelin Berthelot, 75005 Paris, France. Electronic address: jerome.ribot@college-de-france.fr.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Ribot
authors.affiliation: Mathematical Neuroscience Team, CIRB - Collège de France (CNRS UMR 7241, INSERM U1050, UPMC ED 158, MEMOLIFE PSL), 11 Place Marcelin Berthelot, 75005 Paris, France.
authors.forename: Alberto
authors.initials: A
authors.lastname: Romagnoni
authors.affiliation: Brain Rhythms and Neural Coding of Memory, CIRB - Collège de France (CNRS UMR 7241, INSERM U1050, UPMC ED 158, MEMOLIFE PSL), 11 Place Marcelin Berthelot, 75005 Paris, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Milleret
authors.affiliation: Géométrie et dynamique, Université Paris Diderot (Paris VII), Paris, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bennequin
authors.affiliation: Mathematical Neuroscience Team, CIRB - Collège de France (CNRS UMR 7241, INSERM U1050, UPMC ED 158, MEMOLIFE PSL), 11 Place Marcelin Berthelot, 75005 Paris, France; INRIA Mycenae Team, Paris-Rocquencourt, France.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Touboul
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods; D002415:Cats; D007091:Image Processing, Computer-Assisted; D061848:Optical Imaging; D010775:Photic Stimulation; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*
keywords: Cortical maps; Dipole; Orientation; Singularities; Spatial frequency