Nature vs. nurture in the development of tangential connections and functional maps in the visual cortex

Abstract

A series of experiments concerned with mechanisms underlying the development of the visual cortex revealed that long-range tangential connections display at least the following three characteristics: i) in strabismic but not in normally raised cats, intracortical fibers preferentially connect cell groups activated by the same eye (‘ocular dominance selectivity’), ii) within the subsystems of the left and right eye domains, they extend primarily between neurons activated by similar stimulus orientations (‘orientation selectivity’) and iii) they exhibit an anisotropy with respect to the cortical axes by preferentially linking neurons with colinearly aligned receptive fields (‘axial specificity’). These results are compatible with the idea of a selective stabilization of tangential fibers between coactive neurons (the “fire together, wire together” — hypothesis). Optical imaging of functional maps in area 17 of strabismic cats further revealed that iso-orientation domains are continuous across the borders between adjacent ocular dominance columns. This rather supports an experience-independent initial development of orientation preference maps. To what extent spontaneous versus visually driven activity patterns might be involved both in the development of tangential connections and in functional maps is discussed.