The Role of Presynaptic Activity in Monocular Deprivation: Comparison of Homosynaptic Mechanisms
National Academy of Sciences
Proceedings of the National Academy of Sciences
Although there have been extensive investigations in computational neuroscience, the opportunity (that has made such a marked difference in physical sciences) to test detailed and subtle quantitative consequences of a theory against experimental results is rare. In this paper we outline a testable consequence of two contrasting theories of synaptic plasticity applied to the disconnection in visual cortex of the closed eye in monocular deprivation (MD). This disconnection is sometimes thought to be the consequence of a process that stems from a competition of inputs for a limited resource such as neurotrophin. Such a process leads to what we call spatial competition, or heterosynaptic synaptic modification. A contrasting view, exemplified by the Bienenstock, Cooper, and Munro (BCM) theory, is that patterns of input activity compete in the temporal domain. This temporal competition is homosynaptic and does not require a conserved resource. The two erved resource. The two mechanisms, homosynaptic and heterosynaptic, are the distinguishing characteristics of two general classes of learning rules which we explore, using a realistic environment composed of natural scenes. These alternative views lead to opposite dependence on the level of presynaptic activity of the rate of disconnection of the closed eye in monocular deprivation. This strong and testable consequence sets the stage for a critical distinguishing experiment; the experiment has been done and supports the second view. These results have important implications for the processes of learning and memory storage in neocortex.