Impact of structural plasticity on memory formation and decline

Knoblauch, A. (2017). In: Van Ooyen, A., and Butz-Ostendorf, M., eds. The Rewiring Brain: A Computational Approach to Structural Plasticity in the Adult Brain. San Diego: Academic Press, pp. 361-386.

Abstract

This chapter discusses possible functions of structural plasticity for memory formation that follow from simulating and analyzing simple Willshaw- or Hopfield-type network models realizing Hebbian cell assemblies. According to such models, structural plasticity can increase storage efficiency in sparsely connected networks by a factor of at least the inverse filling fraction (of realized potential synapses) or even several orders of magnitude for sparse neural activity as measured experimentally in memory-related cortical areas. A second important function of structural plasticity may be to increase stability of long-term memories by balancing between stability and plasticity and, thus, preventing catastrophic forgetting. Together with the analysis of storage efficiency, this suggests a novel model for efficient memory storage by structural plasticity forming cell assemblies that increase their connectivity and activity but decrease their size. This suggests a role of structural plasticity for sharpening of neural activity as observed experimentally during learning and consolidation. Moreover, structural plasticity can explain several memory phenomena such as the spacing effect or retrograde amnesia much better than alternative models that are solely based on weight plasticity.