Physics (Internal)

Reorganization of columnar architecture in the growing visual cortex

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
The impressive ability of cortical circuits to reorganize during and after the so-called critical period has been demonstrated
in numerous studies by artificially manipulating cortical activity; e.g., by monocular deprivation. But what is the function of 
a period of relatively strong plasticity at such a late stage in normal development? Here, we propose that cortical circuits
may remain plastic for an extended period in development to facilitate themodification of neuronal circuits to adjust for 
cortical growth. In acute and chronic experiments, we study the layout of ocular dominance(OD) columns in cat primary 
visual cortex during a period ofsubstantial postnatal growth. We find that despite a considerable sizeincrease of primary 
visual cortex, the spacing between columns islargely preserved. In contrast, their spatial arrangement changes 
systematically over this period. Whereas in young animals columns are more band-like, layouts become more isotropic 
in mature animals. Interestingly, this reorganization is largest close to the peak of the critical period. We propose a novel 
mechanism of growth-induced reorganization of columnar circuits that is based on the “zigzag instability,” a dynamical 
instability observed in several inanimatepattern-forming systems. We argue that this mechanism is inherent to awide 
class of models for the activity-dependent formation of ODcolumns. Analyzing one representative 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 column width ispreserved by systematic reorganization of 
neuronal selectivitiesduring cortical expansion and that this reorganization is welldescribed by the zigzag instability. Our 
work suggests that corticalplasticity may play an important role in normal development throughfacilitating growth-related 
modifications of neuronal circuits.