Reactivation in Working Memory: An Attractor Network Model of Free Recall

Abstract

The dynamic nature of human working memory, the general-purpose system for processing continuous input, while keeping no longer externally available information active in the background, is well captured in immediate free recall of supraspan word-lists. Free recall tasks produce several benchmark memory phenomena, like the U-shaped serial position curve, reflecting enhanced memory for early and late list items. To account for empirical data, including primacy and recency as well as contiguity effects, we propose here a neurobiologically based neural network model that unifies short- and long-term forms of memory and challenges both the standard view of working memory as persistent activity and dual-store accounts of free recall. Rapidly expressed and volatile synaptic plasticity, modulated intrinsic excitability, and spike-frequency adaptation are suggested as key cellular mechanisms underlying working memory encoding, reactivation and recall. Recent findings on the synaptic and molecular mechanisms behind early LTP and on spiking activity during delayed-match-to-sample tasks support this view.

Memory consolidation from seconds to weeks: a three-stage neural network model with autonomous reinstatement dynamics

“…These include competitive consolidation, effects of primacy and recency in short-term consolidation (not specifically discussed here, see Lansner et al, 2013), retrograde facilitation after impaired acquisition, as well as typical amnesia effects following simulated hippocampal lesions.…”

Working Memory: Maintenance, Updating, and the Realization of Intentions

“…Moreover, the metabolic demands of persistent-activity coding are high (Mongillo et al 2008). Synaptic plasticity as one basis for working memory has been incorporated in various forms in computational models (e.g., O'Reilly et al 1999) based both on non-Hebbian (Mongillo et al 2008) and Hebbian (Lansner et al 2013) synaptic plasticity. The formation of new declarative long-term memories is critically dependent on the mediotemporal/hippocampal brain system and a cascade of cellular events, including longterm potentiation (LTP) (see Squire and Kandel 2000).…”

Brain responses to syntax constrained by time-driven implicit prosodic phrases

“…Everything outside of the focus of attention needs to be retrieved for processing; nevertheless, a set of representations, such as the most recently perceived items in non-focal state, may be temporarily more accessible due to a momentarily heightened level of activation (Jonides et al, 2008). Neural network models of verbal working memory suggest that these activated representations outside of the focus undergo trace decay (Jones & Polk, 2002;Lansner, Marklund, Sikstr€ om, & Nilsson, 2013). Accordingly, temporal decay in activation levels, together with similarity-based interference, are among the main factors that have been proposed to affect information retrieval during language comprehension: memory representations are assumed to receive activation boosts at moments of retrieval or when items with similar features are accessed, and these enhanced states of activation are followed by rapid time-based decay (Lewis & Vasishth, 2005;Vasishth & Lewis, 2006).…”