Experimental effects of removing the ocular dominance map on the organization of the remaining feature maps in visual cortex.

Farley, B.¹, Yu, HB.. ¹, Jin, D.H. ³ and Sur, M. <sup>1, 2

1</sup>Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge MA, USA
²Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge MA, USA
³McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge MA, USA

In visual cortex, receptive field properties change in an orderly way across the tangential dimension, forming multiple overlapping maps of retinotopy, orientation, ocular dominance, and other features. The mechanisms underlying the development of these feature maps are poorly understood. Some computational models can successfully reproduce the structures of multiple feature maps and the characteristic spatial relationships between them; these models suggest that the individual maps develop inter-dependently, in a way that balances smooth mapping of each feature and equal representation of each feature combination. The models predict that changing the structure of (or removing) one of the feature maps early in development should alter the structures of the remaining maps. To test this prediction, we monocularly enucleated ferrets on the day of birth. Anatomically, this manipulation had previously been shown to cause the remaining eye to project uniformly throughout the LGN, rather than to eye-specific patches. Functionally, we find that monocular stimulation in monocularly enucleated animals activates the cortex more uniformly than monocular stimulation in normal animals, and as uniformly as binocular stimulation in normal animals. This indicates that the cortical ocular dominance map is functionally removed following neonatal monocular enucleation. Despite the complete loss of input from one eye, cortical maps of orientation and spatial frequency develop both contralaterally and ipsilaterally to the remaining eye, and their structures are largely unperturbed. Further, their interrelations remain: regions where preferred orientation changes rapidly across the cortex coincide with regions where spatial frequency changes slowly, and vice versa. The results indicate that characteristics of the orientation and spatial frequency maps develop independently of the pattern of ocular dominance, and thus inform theories of feature map development.