Dreaming and the brain: from phenomenology to neurophysiology

“An intriguing possibility concerns the putative antagonism between externally oriented cortical networks and internally oriented, default-mode networks [ 91 ,92].”

“retinotopic cortex is a necessary condition for visual awareness [ 131 ].”

“For example, more than half of nocturnal awakenings reveal the occurrence of imaginary scenes or full-fledged dreams, so it could be dangerous if they gave rise to new declarative memories (Nir and Tononi, 2010).”

“Moreover, the fact that in late sleep many brain regions remain in an ON state while only a minority of areas are in an OFF state may not be unrelated to the increased occurrence and intensity of dreaming in NREM sleep toward the end of the night (Nir and Tononi, 2010).”

“Dreams, the succession of sensorimotor and affective hallucinatory experiences that occur involuntarily during sleep, are prevalent during REM but not confined to it (Nielsen 2000, Nir & Tononi 2010).”

“Increasing anesthetic dosage increases the relative time the neurons are in the down state, which in turn appears to be associated with unconsciousness.(4) As the relative duration of the down states increases, electroencephalographic changes occur with spindle and then wave activity, slow fluctuations in power, and e…”

“A TMS/EEG response similar to that evoked by ketamine can also be recorded during REM sleep [31], a state of high cholinergic tone [32] during which subjects almost invariably experience dreams [33, 34].”

“Furthermore, it has been proposed that during dreams conscious experience is generated partly by the top-down stream [78,79].”

“…involved in, overlap with that of dreaming/REM sleep has also been raised (Fosse and Domhoff, 2007; Pace-Schott, 2007, 2011; Ioannides et al., 2009; Nir and Tononi, 2010), but these comparisons too have remained qualitative: a quantitative meta-analysis has yet to be applied to the question of the…”

“Importantly, a range of studies have outlined dissociations between objective performance and subjective reports, for example in so-called “blindsight” patients [who after lesions of primary visual cortex, lose consciously reportable vision (Persaud et al., 2011)] and in normal subjects (Lau and…”

“AASM sleep stage classification in 30 s epochs has proven high clinical utility, however might be too coarse for scientific approaches (Nir and Tononi, 2010).”

“Areas implicated in memory processing during wake, in particular limbic circuits within the medial temporal lobe, are highly active during REM sleep (Maquet et al., 1996; Braun, 1997; Nofzinger et al., 1997; Braun et al., 1998; Nir and Tononi, 2010).”

“Normally, NE activity is high during wake, low during NREMS, and nearly completely quiescent during REMS [244].”

“It has been demonstrated that the distribution of brain activity in REM sleep is not homogenous (Maquet, 2000; Nir and Tononi, 2010).”

“49 Even individuals who are blinded after the age of 5–7 years appear to have visual imagination and full-fledged dreams with completely realistic visual imagery throughout their life [356], thus indicating the existence of a quite independent and rich phenomenal world.”

“This is in line with neuroimaging studies of REM sleep, demonstrating that neural areas involved in emotion regulation like the amygdala, medial prefrontal cortex and anterior cingulate cortex are highly activated during REM sleep (Nir Tononi, 2010).”

“In addition, the REM sleep state shows the so-called ponto-geniculo-occipital waves, which can even coincide with the phase of the eye movements during REM [45].”

“It has been proposed that dreams themselves would compete and block the processing of external inputs (Nir and Tononi, 2010), but direct evidence is still missing.”

“REM sleep has been linked in healthy volunteers to emotional content and vivid visual imagery (Nir and Tononi, 2010) that could also be present in these patients.”

“One form of disconnection occurs in dreaming, when changes in neuromodulation result in cortical gating of sensory inputs and in inhibition of motor neurons [9].”

“68,69 The occurrence of EEG slow waves is an essential defining characteristic of physiological NREM sleep, the polysomnogram detection of which is dictated by the amplitude and frequency of these slow waves, in addition to other electrographic phenomena such as spindles.”

“Moreover, stimuli largely fail to be incorporated in the content of dreams (Rechtschaffen 1978; Nir and Tononi 2010).”

“…(and, probably, also qualitative) differences in dreams reported after awakening from the two states (Nielsen, 2000), and the peculiar physiology of REM sleep, whose electrophysiological and neurochemical milieu resembles that of wakefulness more than that of NREM sleep (Nir and Tononi, 2010).”

“For example, during dreaming, complex, temporally unfolding episodes can be as intense and vivid as waking experiences, yet sensory stimuli are typically ignored and rarely incorporated into the experience (Koulack, 1969; Nir and Tononi, 2010).”

“Interestingly, during rapid eye movement (REM) sleep, while consciousness exists (dreaming) but is largely unaffected by external sensory stimuli [27], NE signaling is silent.”

“For example, local sleep occurrences in prefrontal cortices could be associated with a lack of awareness and agency such as in dreaming (Nir and Tononi, 2010; Voss et al., 2014).”

“Findings from the former in situ approach as well as the latter retrospective approach indicate that parts of the brain’s DMN, such as the medial prefrontal, temporo-parietal and hippocampal regions, which are involved in intentionality-based imagination, are more strongly associated with dreaming while cognitive cont…”

“…be that studies using fMRI, MEG and/or high-density electroencephalography (hd-EEG) can provide the temporal and spatial resolution necessary, as Nir and Tononi (2010) suggest, especially if used in conjunction with spontaneous NREM morning awakenings similar to those studied by Cicogna et al.…”

“Although REM sleep and its underlying neurophysiological mechanisms were originally believed to be indispensable for dreaming, there has been accumulating evidence that dreaming is dissociable from REM sleep and can be experienced during NREM sleep periods (Nir and Tononi, 2009).”

“Despite recent advances (Wamsley et al, 2010; Dresler et al, 2011; Marzano et al, 2011; Eichenlaub et al, 2013), the cerebral correlates of dreaming remain unclear (Maquet and Ruby, 2004; for reviews, see Hobson, 2005; Nir and Tononi, 2010; Ruby, 2011).”

“Some of these experiences are frequent during normal dream episodes, especially the dissociation between the first-person point of view and the bodily self, while others are more characteristic of lucid dreams (e.g., derealization) (Hobson, 2009; Nir and Tononi, 2010; Thompson, 2014).”

“Sleep is defined as a reversible state in which external stimuli rarely affect perception or elicit meaningful behavioral responses (Nir and Tononi, 2010).”

“The observed brain response to auditory stimulation is, thus, likely uncovering a relatively preserved level of consciousness, without being a signature of a mod-ification of its contents (Nir and Tononi, 2010).”

“…by: Kieran Fox, University of British Columbia, Canada Elizaveta Solomonova, Université de Montréal, Canada *Correspondence: Jennifer M. Windt, Philosophisches Seminar, Johannes Gutenberg-Universität, D-55099 Mainz, Germany e-mail: windt@uni-mainz.de Are dreams subjective experiences during sleep?”

“Or, how would the mnemonicsdream analogy deal with the finding that REM and dreams can be doubly dissociated such that dreams can occur without REM and REM can occur without dreams (Nir & Tononi 2010; Solms 2003a; Solms & Turnbull 2002)?”

“Falling asleep is a gradual phenomenon that includes major changes in behavior, a progressive disconnection from the environment, and marked shifts in the level and content of consciousness, which can vary from the vivid awareness of full-fledged wakefulness to the near-annihilation of experience in early nonrapid eye…”

“Second, although both states enhance mental imagery, there are at least gradual differences between psychedelic states where external stimuli from the body and the outside world are still influencing conscious experience (especially during eyes-open conditions), and dreams, where consciousness is decoupled from the en…”

“In turn, the reduced effect in REM may be viewed as consistent with the rapid forgetting of REM-related memories (dream amnesia; Nir and Tononi, 2010).”

“knows and learned [9].”

“But as many researchers have shown (e.g., Solms, 2000; Domhoff, 2003), REM sleep and dreaming are doubly dissociable, and NREM dreams can take on the typical properties of REM dreams, especially later in the night (Wamsley et al., 2007; Nir and Tononi, 2010; Payne, 2010).”

“of an internally cued cognitive state that underlies dreaming and memory consolidation (Nir and Tononi, 2010).”

“It is also in line with the evidence suggesting that cognitive activity during sleep is more akin to imagination than to perception (91).”

“…dreaming is associated with ‘reduced voluntary control of action and thought’ (Nir and Tononi 2010: 89) as well as ‘altered mnemonic processes’ (Nir and Tononi 2010: 92); both are explained by the absence of certain chemicals required for prefrontal feedback (e.g., dopamine, Hobson 2009)…”

“As such, dreaming reflects pure phenomenality and the importance of dream research in the scientific study of consciousness is now widely acknowledged (e.g., Hobson, 2009; Nir & Tononi, 2010; Revonsuo, 2006; Windt & Noreika, 2011).”

“Dreaming experience and emotions in dreams are not exclusive to phasic REM sleep, and may occur in REM after intervals free of eye movements and in any sleep stage (Desseilles et al., 2011; Nir and Tononi, 2010), especially late Stage 2 of non-REM sleep (Antrobus et al., 1995).”

“Neuroscientific studies of the neural space support this intuition: during dreaming, most of the DMN deactivates, as well as the extrinsic system (Nir and Tononi, 2010).”

“Recent speculations have focused on the brain’s “default network” as a possible neural substrate of dreaming (Pace-Schott, 2007, 2011a,b; Nir and Tononi, 2010; Wamsley and Stickgold, 2010; Domhoff, 2011).”

“Although there may be differences between thoughts that occur during wakefulness and dreaming, including reduced metacognitive insight (Nir & Tononi, 2010), several studies have suggested that the overall phenomenology of consciousness is remarkably similar across sleep and wake (Kahan & LaBerge,…”

“This is in principle similar to the way one attempts to identify sleep and dreams objectively by looking for characteristic brain activity signatures (Nir and Tononi, 2010).”

“…awakenings, such as the experimental setting (Schredl, 2008), the physiological background of waking-life and by individual variables, such as personality, cognitive functions, censure/ omissions and socio-cultural features (Nir & Tononi, 2010), making dream reports not always completely reliable.”

“…related to dream phenomenology: Activation of visual association areas is in line with vivid imagery, amygdala activation with dream emotionality, and DLPFCdeactivationwith the lack of insight, reflexivity and volition commonly experienced in dreams (Hobson & Pace-Schott, 2002; Nir & Tononi, 2010).”

“Brain activity during REM sleep in humans is considered to be well understood (Hobson and Pace-Schott, 2002; Schwartz and Maquet, 2002; Nir and Tononi, 2010), but several results question this notion.”

“Attention is unstable and rigidly focused, facts and reality are not checked, violation of physical laws and bizarreness are passively accepted, contextual congruence is distorted and time is altered (Rechtschaffen, 1978; Hobson, 2009; Nir & Tononi, 2010).”

“Likewise, independent studies during sleep and anesthesia (in which retrospective reports can be obtained on awakening) demonstrate that subjective experience frequently occurs even in the absence of any behavioral responsiveness [17, 18].”

“Studying mental experiences during sleep offers a unique opportunity to explain how changes in brain activity relate to changes in consciousness (Hobson et al. 1998 ; Rees et al. 2002 ; Nir and Tononi 2010 ) .”

“occur in non REM sleep (Nir and Tononi, 2010).”

“In this regard, some recent studies have shown progress by focusing on increasingly brief dream events and more precise neurophysiological signals (see review in Nir and Tononi, 2010).”