Does abnormal non-rapid eye movement sleep impair declarative memory consolidation?: Disturbed thalamic functions in sleep and memory processing.

Non-rapid eye movement (NREM) sleep has recently garnered support for its role in consolidating hippocampus-based declarative memories in humans. We provide a brief review of the latest research on NREM sleep activity and its association with declarative memory consolidation. Utilizing empirical findings from sleep studies on schizophrenia, Alzheimer's disease, and fibromyalgia, we argue that a significant reduction of slow-wave sleep and sleep spindle activity contribute to the development of deficits in declarative memory consolidation along with concomitant sleep disturbances commonly experienced in the aforementioned disorders. A tentative model is introduced to describe the mediating role of the thalamocortical network in disruptions of both declarative memory consolidation and NREM sleep. The hope is to stimulate new research in further investigating the intimate link between these two very important functions.