Reorganization of columnar architecture in the growing visual cortex

TL;DR

This study investigates how ocular dominance columns in the cat visual cortex reorganize during postnatal growth, revealing a preserved spacing but changing spatial arrangements driven by a growth-induced instability.

Contribution

It introduces a novel growth-induced reorganization mechanism based on the zigzag instability, supported by modeling with the Elastic Network model.

Findings

Column spacing remains largely preserved during growth.

Spatial arrangement of columns becomes more isotropic in mature animals.

Reorganization is driven by a growth-induced zigzag instability.

Abstract

Many cortical areas increase in size considerably during postnatal development, progressively displacing neuronal cell bodies from each other. At present, little is known about how cortical growth affects the development of neuronal circuits. Here, in acute and chronic experiments, we study the layout of ocular dominance (OD) columns in cat primary visual cortex (V1) during a period of substantial postnatal growth. We find that despite a considerable size increase of V1, the spacing between columns is largely preserved. In contrast, their spatial arrangement changes systematically over this period. While in young animals columns are more band-like, layouts become more isotropic in mature animals. We propose a novel mechanism of growth-induced reorganization that is based on the `zigzag instability', a dynamical instability observed in several inanimate pattern forming systems. We argue that this mechanism is inherent to a wide class of models for the activity-dependent formation of OD columns. Analyzing one member of this class, the Elastic Network model, we show that this mechanism can account for the preservation of column spacing and the specific mode of reorganization of OD columns that we observe. We conclude that neurons systematically shift their selectivities during normal development and that this reorganization is induced by the cortical expansion during growth. Our work suggests that cortical circuits remain plastic for an extended period in development in order to facilitate the modification of neuronal circuits to adjust for cortical growth.