Runaway synaptic modification in models of cortex: Implications for Alzheimer's disease

-In models of cortex, the spread of actwtty along prevlously strengthened synapses durmg synapttc modtficatton can result m an exponenttal growth of a large number of synaptlc connecttons, here termed runaway synaptlc modtficatton Analysts of thts phenomenon may provide a theoretwal framework for descrlbmg the mtttatwn and progresswn of the cortwal neuronal degeneration found m Alzhetmer's dtsease Here. the dynamics of learmng m a cortical model are described, focusing on the exponenttal growth produced by allowmg synaptw transmtsston at prevtously modtfied synapses durmg learnmg of a new pattern It ts shown that suppression of synapttc transmission during learnmg can prevent the strengthenmg of undeswed connections, whtle allowing destred connecttons to grow raptdly However, an tmbalance of corttcal parameters, or storage of overlappmg patterns in excess of capacity, can lead to interference during learmng and runaway synapttc mod~catton This runaway synaptic modlficatwn can progress between different regtons These phenomena are discussed with reference to the neuropathologtcal evtdence on the mttiatton and progresston of neuronal degenerauon m Alzhetmer's disease and the behavtoral evMence on associated memory deficits Keywords--Associative memory, Stability, Hippocampus, Learning, Alzheimer's disease, Interference.