Behavioural Brain Research 226 (2012) 592–596 Contents lists available at SciVerse ScienceDirect Behavioural Brain Research jo u r n al hom epa ge: www.elsevier.com/locate/bbr Review How we remember the stuff that dreams are made of: Neurobiological approaches to the brain mechanisms of dream recall Luigi De Gennaro a,* , Cristina Marzano a , Carlo Cipolli b , Michele Ferrara c a Department of Psychology, University of Rome “Sapienza”, Italy b Department of Psychology, University of Bologna, Italy c Department of Health Sciences, University of L’Aquila, Italy a r t i c l e i n f o Article history: Received 29 September 2011 Accepted 11 October 2011 Available online 17 October 2011 Keywords: Dream recall Brain damage Intracranial recordings EEG oscillations Diffusion tensor imaging Subcortical nuclei Local sleep a b s t r a c t Intrinsic and historical weaknesses delayed the spread of a sound neurobiological investigation on dreaming. Nevertheless, recent independent findings confirm the hypothesis that the neurophysiologi- cal 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 neu- rophysiological mechanisms underlying episodic/declarative memory formation may be the same across different states of consciousness. © 2011 Elsevier B.V. All rights reserved. Contents 1. Introduction to the neurobiological investigation on dreams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 2. Dreaming in brain damaged patients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593 3. Neuroimaging studies: functional measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 4. Neuroimaging studies: morphoanatomical measures of subcortical nuclei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594 5. Local (cortical) electrophysiology of sleep and dream recall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 6. Concluding remarks and future perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 1. Introduction to the neurobiological investigation on dreams The production of dreams during sleep is a largely unex- plained phenomenon of human existence, and its underlying brain mechanisms are mostly unknown. This is mainly due to the unac- cessibility of dreams to a direct study, but only by using dream * Corresponding author at: Dept. of Psychology – Section of Neuroscience, Univer- sity of Rome “Sapienza”, Via dei Marsi, 78, 00185 Rome, Italy. Tel.: +39 06 49917647; fax: +39 06 49917711. E-mail address: luigi.degennaro@uniroma1.it (L. De Gennaro). recall after spontaneous or provoked awakening from sleep. Like the Schrodinger’s Cat, we can investigate dreaming only interrupt- ing dream experience and, in this way, altering the physiological scenario in which dreams are produced (i.e., the electrical and neurochemical characteristics of sleep stages). Until innovative protocols – which might overcome this apparently insurmount- able obstacle – will be introduced, neurobiological investigation is necessarily limited to the brain mechanisms of dream recall. Almost inevitably related to the issue of this indirect access to dreaming, the study of brain mechanisms of dreams has been mainly restricted to rapid eye movement sleep (REMS), implicitly assuming that dreams are strictly dependent on its specific physi- ology. This assumption was essentially based on the initial finding 0166-4328/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2011.10.017