Local cortical interactions determine the form of cortical plasticity

Competitive interactions between left and right eye inputs to visual cortex during development are usually explained by the thalamocortical axons comp eting more or less well for cortical territory during retraction into eye s pecific domains. Here me review the evidence for competitive and co-operati ve interactions between cortical columns in barrel cortex which are present several weeks after retraction of thalamocortical axons into barrels. Sens ory responses in barrel cortex can be altered by a period of vibrissa depri vation. It was found that responses to previously deprived vibrissae (that had been allowed to regrow) were depressed more if neighboring vibrissae we re spared than if all vibrissae were removed simultaneously, Depression of the deprived vibrissa response was greater the closer the cell lay to a spa red barrel. It was also found that spared vibrissae responses were potentia ted more if several neighboring vibrissae were left intact than if only a s ingle vibrissae was spared. These results suggest a mechanism of cooperativ e potentiation, perhaps due to intracortical summation of excitation evoked by neighbouring vibrissa stimulation. Thalamic responses to vibrissa stimu lation were unaffected by deprivation indicating a cortical origin. One of the consequences of deprivation was that the speed of transmission between barrels was increased for spared and decreased for deprived vibrissa. These results imply that inherent interactions between cortical columns give ris e to a property of competition and co-operativity which amplify the effects of sensory deprivation. (C) 1999 John Wiley & Sons, Inc.