Autobiographical memory and hyperassociativity in the dreaming brain: implications for memory consolidation in sleep

Abstract

In this paper we argue that autobiographical memory (AM) activity across sleep and wake can provide insight into the nature of dreaming, and vice versa. Activated memories within the sleeping brain reflect one's personal life history (autobiography). They can appear in largely fragmentary forms and differ from conventional manifestations of episodic memory. Autobiographical memories in dreams can be sampled from non-REM as well as REM periods, which contain fewer episodic references and become more bizarre across the night. Salient fragmented memory features are activated in sleep and re-bound with fragments not necessarily emerging from the same memory, thus de-contextualizing those memories and manifesting as experiences that differ from waking conceptions. The constructive nature of autobiographical recall further encourages synthesis of these hyper-associated images into an episode via recalling and reporting dreams. We use a model of AM to account for the activation of memories in dreams as a reflection of sleep-dependent memory consolidation processes. We focus in particular on the hyperassociative nature of AM during sleep.

Keywords: autobiographical memory; continuity hypothesis; dreaming; hyperassociativity; memory consolidation; sleep.

FIGURE 1

AM consolidation model. Waking experiences are schematically represented as a circle, each containing numerous constituent fragments. Individual elements (such as characters, colors, objects present, sounds, etc.) feature alongside an action (such as shouting at a colleague) and a context (such as the environmental setting and an emotional tone). Focused waking cognition involves the selective activation of semantic associations to some of the fragments. The corresponding dream involves the synthesis of different fragments (elements, actions and a context, plus their possible associations) taken from previous waking experiences. Each of those fragments could elicit a hyperassociation. The consolidated elements are those that have been repeatedly or strongly activated. They remain preferentially accessible following sleep.