ReviewHow we remember the stuff that dreams are made of: Neurobiological approaches to the brain mechanisms of dream recall
Highlights
► Dreaming and episodic memory encoding may share similar brain mechanisms. ► Sleep EEG oscillations predict successful dream recall. ► Functional anatomy of hippocampus–amygdala correlates with dream features.
Section snippets
Introduction to the neurobiological investigation on dreams
The production of dreams during sleep is a largely unexplained phenomenon of human existence, and its underlying brain mechanisms are mostly unknown. This is mainly due to the unaccessibility of dreams to a direct study, but only by using dream recall after spontaneous or provoked awakening from sleep. Like the Schrodinger's Cat, we can investigate dreaming only interrupting dream experience and, in this way, altering the physiological scenario in which dreams are produced (i.e., the electrical
Dreaming in brain damaged patients
The so-called “neuropsychology of dreaming” has evaluated dream features in patients with selective brain lesions and provided univocal evidences that confirmed the assumption that phenomenology of dreams is closely related to the brain activity and organization. Preliminary neuropsychological observations were addressed to the brainstem, in keeping with the view that the high co-occurrence of REM sleep and dream recall implies that brainstem mechanisms are also responsible of dream generation.
Neuroimaging studies: functional measures
Neuroimaging techniques like Positron Emission Tomography (PET), using H215O measurements of regional cerebral blood flow (rCBF), have allowed to describe a functional neuroanatomy of human sleep and the possible correlates of dream features. Although consistent evidence has been provided on dream recall upon awakenings from any stage of NREM sleep [2], [4], neuroimaging studies mostly focused their attention on the peculiar association between REM sleep and dreaming, in order to identify which
Neuroimaging studies: morphoanatomical measures of subcortical nuclei
Neuroimaging measures and intracranial recordings delineate a fairly coherent picture of how two deep grey matter structures may play a pivotal role in dreaming: the hippocampus and the amygdala.
The specific activity of the hippocampus should mediate the partial reproduction of memories of events occurred during wakefulness into dream contents. The first evidence in favour of this hypothesis was provided by studies using intracranial recordings in epileptic patients, which showed that
Local (cortical) electrophysiology of sleep and dream recall
In the last decades, a large body of evidence corroborated the hypothesis that sleep is not a spatially global and uniform state. Indeed, the application of the technical advancements (i.e., multichannel sleep EEG and Fast Fourier Transform – FFT – analyses of EEG) allowed to evaluate the spatio-temporal dynamics EEG during sleep, showing that the homeostatic dynamics of EEG power in the recovery process are intrinsically local and did not involve the whole cerebral cortex to the same extent
Concluding remarks and future perspectives
Neurobiological evidences discussed in this review, by integrating findings from different approaches and methods, depicts a fairly coherent picture that emphasizes the continuity between cortical and subcortical mechanisms of waking and sleep cognitive activity [40], [41]. Regional EEG results suggest that the electrophysiological mechanisms involved in encoding and recall of episodic memories across wakefulness and sleep are the same [39]. Brain lesions and functional neuroanatomy of healthy
Acknowledgements
This work was partly supported by the Compagnia di San Paolo, Programma Neuroscienze 2008/09 (3889 SD/sd, 2008.1300 to L.D.G), in the form of a fellow grant to C.M., and by the Fondazione Cassa di Risparmio di Bologna (Project n. 2008.2443 to C.C.).
References (41)
- et al.
Cyclic variations in EEG during sleep and their relation to eye movements, body mobility and dreaming
Electroencephalogr Clin Neurophysiol
(1957) Chronobiological features of dream production
Sleep Med Rev
(2004)Mental activity during sleep
Sleep Med Rev
(2002)- et al.
Right hemispheric mediation of dream visualization: a case study
Cortex
(1981) - et al.
To dream or not to dream? Relevant data from new neuroimaging and electrophysiological studies
Curr Opin Neurobiol
(1998) - et al.
Forebrain activation in REM sleep: an FDG PET study
Brain Res
(1997) - et al.
Procedural learning and sleep hippocampal low frequencies in humans
Neuroimage
(2008) - et al.
Functional role of gamma and theta oscillations in episodic memory
Neurosci Biobehav Rev
(2010) Dreams in patients with sleep disorders
Sleep Med Rev
(2009)A review of mentation in REM and NREM sleep: covert REM sleep as a possible reconciliation of two opposing models
Behav Brain Sci
(2000)
Dreaming and rem sleep are controlled by different brain mechanisms
Behav Brain Sci
Sleep and sleep electroencephalogram in depressed patients treated with phenelzine
Arch Gen Psychiatry
Die Seelenblindheit als Herderscheinung und ihre Beziehung zur Alexie und Agraphie
Ein Beitrag zur Kenntniss der Seelenblindheit
Arch Psychiatr Nervenkrank
Dream recall in brain-damaged patients: a contribution to the neuropsychology of dreaming through a review of the literature
The neuropsychology of dreaming: a clinico-anatomical study
Clinical survey and results of 200 cases of prefrontal leucotomy
J Ment Sci
Pre-frontal leucotomy: a survey of 300 cases personally followed for 1–3 years
Dreaming: a neuropsychological view
Schweiz Arch Neurol Psychiatr
Regional cerebral blood flow throughout the sleep-wake cycle. An H2(15)O PET study
Brain
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2019, CortexCitation Excerpt :Dreaming has been consistently observed during both REM and NREM sleep, although it appears to be more frequent and perhaps more emotionally charged during REM (e.g., Cipolli, Ferrara, De Gennaro, & Plazzi, 2017; Hobson, Pace-Schott, & Stickgold, 2000; Nir & Tononi, 2010; Solms, 2000). Numerous authors have therefore drawn a speculative link between the high levels of amygdala activation during REM and the intensity of emotional experiences reported in dreams, and have also indicated that amygdala activity during REM may be linked to the processing and depotentiation of emotional memories (e.g., Dang-Vu et al., 2005; De Gennaro, Marzano, Cipolli, & Ferrara, 2012; Deliens, Gilson, & Peigneux, 2014; Deseilles, Dang-Vu, Sterpenich, & Schwartz, 2011; Maquet et al., 1996; Nielsen & Stenstrom, 2005; Nir & Tononi, 2010; Nishida, Pearsall, Buckner, & Walker, 2009; Pace-Schott, Germain, & Milad, 2015; Palagini & Rosenlicht, 2011; Perogamvros & Schwartz, 2012; Popa, Duvarci, Popescu, Lena, & Pare, 2010; Van Der Helm et al., 2011). The depotentiation of emotional memories by the limbic system during sleep is the neurophysiological side of the emotional regulation hypothesis of dreaming (e.g., Hartman 1996; Levin & Nielsen, 2007; Cartwright, 1991; Wright & Koulack, 1987; for a review see; Malinowski & Horton, 2015) and is supported by recent results showing that dreams temper the emotional intensity of emotional memories (Vallat, Chatard, Blagrove, & Ruby, 2017).
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2019, Handbook of Behavioral NeuroscienceCitation Excerpt :However, despite these limitations, it should be emphasized that alpha (as well as theta) activity plays a pivotal role in the retrieval of the episodic amnestic traces during wakefulness (Klimesch, 1999; Molle, Marshall, Fehm, & Born, 2002). In light of these considerations, it has been hypothesized that the neural mechanisms responsible for dream recall resemble those responsible for the encoding and retrieval of episodic memories during wakefulness (De Gennaro et al., 2012; Scarpelli, D’Atri, et al., 2015), a notion that fits well with the neuroimaging findings (discussed above) regarding the overlap in brain mechanisms for the consolidation of emotional memories during waking and dreaming (De Gennaro et al., 2011, 2016). However, some empirical findings are not consistent with this view.
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2017, Sleep Medicine ReviewsCitation Excerpt :This (often implicit) assumption has deeply influenced the experimental investigation of dreaming, first developed in the 1950s after the discovery of the cyclic architecture of sleep and the identification of rapid eye movement (REM) sleep as a possible neurophysiological marker of dreaming. However, recent neuroimaging and neurophysiological studies on resting state and mind wandering in wakefulness have shown a wide overlap of phenomenological features and underlying brain mechanisms [3,4] with dreaming. This has led to a conceptualization of dreaming as a “natural” extension of waking consciousness [5], namely, a state characterized by internally generated multisensorial (overall visual and auditory), motor (sometimes dramatic), cognitive and emotional experiences, inserted as fairly coherent events into an imaginary story-like plot [3,6–8].