Dreams as Virtual Reality Simulations
REM sleep taps a vast network of brain structures to simulate alternate worlds
In a recent paper in the Proceedings of the National Academies of Science by Chow et al (Chow HM, Horovitz SG, Carr WS, Picchioni D, Coddington N, Fukunaga M, Xu Y, Balkin TJ, Duyn JH, Braun AR. Rhythmic alternating patterns of brain activity distinguish rapid eye movement sleep from other states of consciousness.Proc Natl Acad Sci U S A. 2013 Jun 18;110(25):10300-5. doi: 10.1073/pnas.1217691110. Epub 2013 Jun 3. Erratum in: Proc Natl Acad Sci U S A. 2013 Aug 6;110(32):13228), the authors reported some interesting new data as to how brain activity patterns differ in REM sleep as compared to waking consciousness and slow wave sleep (SWS). Using resting state functional connectivity (fcMRI) methods these authors imaged the brains of young sleep deprived persons while they caught up on their sleep in the scanner. Adequate data were obtained from nine subjects who had at least 30 minutes (600 fMRI volumes) of SWS and four subjects who had at least 5 minutes (100 fMRI volumes) of REM sleep each. The total REM sleep duration for the four subjects included in this study was 32.4 min, corresponding to 648 fMRI volumes.
Using this admittedly limited dataset the authors were nevertheless able to observe functional uncoupling of the default mode network (DMN) during SWS and recoupling during REM sleep (similar to wakefulness). REM was further characterized by a more widespread, temporally dynamic interaction between two major brain systems: a diverse collection of unimodal sensorimotor areas and a similarly diverse collection of higher-order association cortices (including the DMN). During REM, the sensorimotor collection seems to turn on and off complimentary to that of the higher order association collection in reciprocally alternating multisecond epochs with a frequency ranging from 0.1 to 0.01 Hz.
These observations of the unique brain activation patterns associated with REM give us much more detail than that obtained from the first spate of neuroimaging studies down on REM in the last decade. Those studies essentially told us that REM was characterized by activation in the amygdala and limbic regions and deactivation or downregulation in the prefrontal cortex. Since these early studies, neuroimaging work on REM in recent years has confirmed the earlier work but added to it the fact that that REM is also consistently associated with activation in the default mode network—that collection of structures that very reliably are activated whenever we sit quietly being attentive and aware of self andenvironment. The posterior cingulate cortex is the linchpin structure in the DMN mediating interactions between brainstem sites and higher order cognitive centers like the medial prefrontal cortex (MPFC). Note that the prefrontal cortex (PFC) is part of the DMN and it is activated during REM. It appears that only dorsal portions of the PFC are downregulated in REM.
Chow et al add to this picture that REM is associated with activation of an even larger collection of structures than those found in the DMN and that REM embodies a dynamic system of interacting large scale brain networks—specially primary sensorimotor systems and higher order association cortices that presumably handle complex cognitive processes. In short primary sensory/motor centers appear to interact with complex cognitive centers during REM.
Chow et al note that these set of activation patterns is consistent with the idea that REM sleep is running complex mental simulations that we would experience as dreams. There have been many scientists (myself included) who have pointed out that dreams cannot be mere nonsense given the elaborate, complex, involuntary and highly structured formal features of dreams. These features boil down to the fact that dreams are extraordinarily complex mental simulations. The eminent dream and brain researchers Allan Hobson and Karl Friston have called the dreaming brain a virtual reality machine (e.g., Hobson JA, Hong CC, Friston KJ. Virtual reality and consciousness inference in dreaming. Front Psychol. 2014 Oct 9;5:1133. doi: 10.3389/fpsyg.2014.01133. eCollection 2014) precisely in order to emphasize this capacity of the dreaming brain. Now of course the waking brain also performs simulations so it too is a predictive virtual reality machine that runs simulations of expected events all the time. But the waking brain uses differing sets of brain networks to run these simulations than does the dreaming brain.
The crucial question concerns the differing contents of waking vs REM vs other sleep state simulations...We need to ask how does content of REM simulations differ from content of waking and other sleep state simulations? REM simulations differ from waking simulations but in what respects? I have argued and presented evidence for the claim that REM simulations are filled with aggression relative to waking or other sleep state simulations but that I suspect is only the tip of the iceberg.
Thanks:psychologytoday
Thanks:psychologytoday
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