How we remember the stuff that dreams are made of: neurobiological approaches to the brain mechanisms of dream recall

Abstract

Intrinsic and historical weaknesses delayed the spread of a sound neurobiological investigation on dreaming. Nevertheless, recent independent findings confirm the hypothesis that the neurophysiological mechanisms of encoding and recall of episodic memories are largely comparable across wakefulness and sleep. Brain lesion and neuroimaging studies converge in indicating that temporo-parieto-occipital junction and ventromesial prefrontal cortex play a crucial role in dream recall. Morphoanatomical measurements disclose some direct relations between volumetric and ultrastructural measures of the hippocampus-amygdala on the one hand, and some specific qualitative features of dreaming on the other. Intracranial recordings of epileptic patients also provide support for the notion that hippocampal nuclei mediate memory formation during sleep as well as in wakefulness. Finally, surface EEG studies showed that sleep cortical oscillations associated to a successful dream recall are the same involved in encoding and recall of episodic memories during wakefulness. Although preliminary, these converging pieces of evidence strengthen the general view that the neurophysiological mechanisms underlying episodic/declarative memory formation may be the same across different states of consciousness.