title: Modulation of orientation-selective neurons by motion: when additive, when multiplicative?
abstract: The recurrent interaction among orientation-selective neurons in the primary visual cortex (V1) is suited to enhance contours in a noisy visual scene. Motion is known to have a strong pop-up effect in perceiving contours, but how motion-sensitive neurons in V1 support contour detection remains vastly elusive. Here we suggest how the various types of motion-sensitive neurons observed in V1 should be wired together in a micro-circuitry to optimally extract contours in the visual scene. Motion-sensitive neurons can be selective about the direction of motion occurring at some spot or respond equally to all directions (pandirectional). We show that, in the light of figure-ground segregation, direction-selective motion neurons should additively modulate the corresponding orientation-selective neurons with preferred orientation orthogonal to the motion direction. In turn, to maximally enhance contours, pandirectional motion neurons should multiplicatively modulate all orientation-selective neurons with co-localized receptive fields. This multiplicative modulation amplifies the local V1-circuitry among co-aligned orientation-selective neurons for detecting elongated contours. We suggest that the additive modulation by direction-specific motion neurons is achieved through synaptic projections to the somatic region, and the multiplicative modulation by pandirectional motion neurons through projections to the apical region of orientation-specific pyramidal neurons. For the purpose of contour detection, the V1-intrinsic integration of motion information is advantageous over a downstream integration as it exploits the recurrent V1-circuitry designed for that task.
authors.affiliation: Computational Neuroscience Group, Department of Physiology, University of Bern Bern, Switzerland.
authors.forename: Torsten
authors.initials: T
authors.lastname: Lüdge
authors.affiliation: Computational Neuroscience Group, Department of Physiology, University of Bern Bern, Switzerland.
authors.forename: Robert
authors.initials: R
authors.lastname: Urbanczik
authors.affiliation: Computational Neuroscience Group, Department of Physiology, University of Bern Bern, Switzerland.
authors.forename: Walter
authors.initials: W
authors.lastname: Senn
keywords: V1; additive modulation; contour detection; gain modulation; illusions; model; motion