RUNAWAY SYNAPTIC MODIFICATION IN MODELS OF CORTEX - IMPLICATIONS FOR ALZHEIMERS-DISEASE

In models of cortex, the spread of activity along previously strengthe ned synapses during synaptic modification can result in an exponential growth of a large number of synaptic connections, here termed runaway synaptic modification. Analysis of this phenomenon may provide a theo retical framework for describing the initiation and progression of the cortical neuronal degeneration found in Alzheimer's disease. Here, th e dynamics of learning in a cortical model are described, focusing on the exponential growth produced by allowing synaptic transmission at p reviously modified synapses during learning of a new pattern. It is sh own that suppression of synaptic transmission during learning can prev ent the strengthening of undesired connections, while allowing desired connections to grow rapidly. However, an imbalance of cortical parame ters, or storage of overlapping patterns in excess of capacity, can le ad to interference during learning and runaway synaptic modification. This runaway synaptic modification can progress between different regi ons. These phenomena are discussed with reference to the neuropatholog ical evidence on the initiation and progression of neuronal degenerati on in Alzheimer's disease and the behavioral evidence on associated me mory deficits.