  Theories and models of working memory (WM) were at least since the mid-1990s
dominated by the persistent activity hypothesis. The past decade has seen
rising concerns about the shortcomings of sustained activity as the mechanism
for short-term maintenance of WM information in the light of accumulating
experimental evidence for so-called activity-silent WM and the fundamental
difficulty in explaining robust multi-item WM. In consequence, alternative
theories are now explored mostly in the direction of fast synaptic plasticity
as the underlying mechanism.The question of non-Hebbian vs Hebbian synaptic
plasticity emerges naturally in this context. In this review we focus on fast
Hebbian plasticity and trace the origins of WM theories and models building on
this form of associative learning.
