Environmental Modification of the Visual Cortex and the Neural Basis of Learning and Memory

IN the primary visual cortex of a normal cat the neurones are almost all orientation detectors, which respond only if an edge or bar at the appropriate angle moves across the receptive field: all orientations are equally represented¹. But early experience can grossly modify the visual cortex. Blakemore and Cooper² reared two kittens in the dark except for a few hours each day spent in cylindrical chambers painted with black and white stripes at one orientation. These two animals, which experienced almost 300 h of exposure to stripes during their first 5 months of life, had no cortical neurones responding to the orientation perpendicular to the stripes that they saw when they were young. Almost all their cortical cells preferred orientations within 45 deg of the experienced angle. The phenomenon involves active modification of the receptive fields of the neurones, and not mere degeneration of unused cells, because there were no regions of silent cortex and no histological evidence of degeneration.