Power-law forgetting in synapses with metaplasticity

TL;DR

This paper introduces two models of metaplastic synapses demonstrating power-law forgetting, highlighting how different decay mechanisms influence transient responses but share a universal long-term forgetting behavior.

Contribution

The paper develops and compares two novel models of metaplastic synapses with distinct decay mechanisms, revealing universal power-law forgetting behavior.

Findings

Both models exhibit power-law forgetting with the same exponent.

Transient responses differ based on decay mechanisms.

Long-term memory decay follows a universal power-law pattern.

Abstract

The idea of using metaplastic synapses to incorporate the separate storage of long- and short-term memories via an array of hidden states was put forward in the cascade model of Fusi et al. In this paper, we devise and investigate two models of a metaplastic synapse based on these general principles. The main difference between the two models lies in their available mechanisms of decay, when a contrarian event occurs after the build-up of a long-term memory. In one case, this leads to the conversion of the long-term memory to a short-term memory of the opposite kind, while in the other, a long-term memory of the opposite kind may be generated as a result. Appropriately enough, the response of both models to short-term events is not affected by this difference in architecture. On the contrary, the transient response of both models, after long-term memories have been created by the passage of sustained signals, is rather different. The asymptotic behaviour of both models is, however, characterised by power-law forgetting with the same universal exponent.