Retinotopic maps of many visual areas are thought to follow the fundamental principles described for the primary visual cortex (V1), where nearby points on the retina map to nearby points on the surface of V1, and orthogonal axes of the retinal surface are represented along orthogonal axes of the cortical surface. Here we demonstrate a striking departure from this mapping in the secondary visual area (V2) of the tree shrew best described as a sinusoidal transformation of the visual field. This sinusoidal topography is ideal for achieving uniform coverage in an elongated area like V2, as predicted by mathematical models designed for wiring minimization, and provides a novel explanation for periodic banded patterns of intra-cortical connections and functional response properties in V2 of tree shrews as well as several other species. Our findings suggest that cortical circuits flexibly implement solutions to sensory surface representation, with dramatic consequences for large-scale cortical organization.
A sinusoidal transformation of the visual field is the basis for periodic maps in area V2
V1-V2 connectivity is sufficient to produce sinusoidal retinotopy in V2 from conformal retinotopy in V1.
(A) Relationship between maps in V1 and V2 under a conformal or planar (left) and sinusoidal (right) transformation.
(B) Axon terminals in V2 produced from tdtomato AAV virus injections in V1 along an iso-azimuth axis in flattened section of left hemisphere (left) compared with the prediction from a sinusoidal transform of V1 (right). (C) Axon terminals in V2 produced from multi-colored AAV virus injections in V1 along the elevation-encoding axis (left) or azimuth-encoding axis (right). (D) Axon terminals in V2 produced by two focal AAV virus injections in V1 away from the V1/V2 border. (E) Multiple axon patches in V2 produced by injection of the tdtomato AAV virus in V1 outside of the cranial window, imaged in vivo using a red filter (top) and azimuth map in same animal overlapped with axon projection contours (bottom).
Max Planck Florida Institute for Neuroscience
