Coexistence of short and long term memory in a model network of realistic neurons

Abstract

NMDA-mediated synaptic currents are believed to influence LTP. A recent model (Lisman et al., Nature Neurosci. (1993) 273–275) demonstrates that they can instead support short term memory based on rhythmic spike activity. We examine this effect in a more realistic model that uses two-compartment neurons experiencing fatigue and also includes long-term memory by synaptic LTP. We find that the network does support both modes of operation without any parameter changes, but depending on the input patterns. Short term memory functionality might facilitate Hebbian learning through LTP by holding a new pattern while synaptic potentiation occurs. We also find that susceptibility of the short term memory against new input is time-dependent and reaches a maximum around the time constant of neuronal fatigue (200– 400 ms ). This corresponds well to the time scale of the syllabic rhythm and various psychophysical phenomena.