Sleep researchers in different disciplines disagree about how fully dreaming can be explained in terms of brain physiology. Debate has focused on whether REM sleep dreaming is qualitatively different from nonREM (NREM) sleep and waking. A review of psychophysiological studies shows clear quantitative differences between REM and NREM mentation and between REM and waking mentation. Recent neuroimaging and neurophysiological studies also differentiate REM, NREM, and waking in features with phenomenological implications. Both evidence and theory suggest that there are isomorphisms between the phenomenology and the physiology of dreams. We present a three-dimensional model with specific examples from normally and abnormally changing conscious states.

/pdf/dreaming-and-the-brain-toward-a-cognitive-neuroscience-of-4pu7cg288c.pdf

Dreaming and the brain: toward a cognitive neuroscience of conscious states

Converging evidence and new research methodologies from across the neurosciences permit the neuroscientific study of the role of sleep in off-line memory reprocessing, as well as the nature and function of dreaming. Evidence supports a role for sleep in the consolidation of an array of learning and memory tasks. In addition, new methodologies allow the experimental manipulation of dream content at sleep onset, permitting an objective and scientific study of this dream formation and a renewed search for the possible functions of dreaming and the biological processes subserving it.

https://www.cogsci.ucsd.edu/~pineda/COGS175/readings/Stickgold.pdf

Sleep, learning, and dreams: off-line memory reprocessing

Several theories claim that dreaming is a random by-product of REM sleep physiology and that it does not serve any natural function. Phenomenal dream content, however, is not as disorganized as such views imply. The form and content of dreams is not random but organized and selective: during dreaming, the brain constructs a complex model of the world in which certain types of elements, when compared to waking life, are underrepresented whereas others are over represented. Furthermore, dream content is consistently and powerfully modulated by certain types of waking experiences. On the basis of this evidence, I put forward the hypothesis that the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance. To evaluate this hypothesis, we need to consider the original evolutionary context of dreaming and the possible traces it has left in the dream content of the present human population. In the ancestral environment human life was short and full of threats. Any behavioral advantage in dealing with highly dangerous events would have increased the probability of reproductive success. A dream-production mechanism that tends to select threatening waking events and simulate them over and over again in various combinations would have been valuable for the development and maintenance of threat-avoidance skills. Empirical evidence from normative dream content, children's dreams, recurrent dreams, nightmares, post traumatic dreams, and the dreams of hunter-gatherers indicates that our dream-production mechanisms are in fact specialized in the simulation of threatening events, and thus provides support to the threat simulation hypothesis of the function of dreaming.

https://www.unil.ch/files/live/sites/ln/files/shared/Revonsuo_1.pdf

The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming

The notion that dreaming might alter the strength of associative links in memory was first proposed almost 200 years ago. But no strong evidence of such altered associative links has been obtained. Semantic priming can be used to quantify the strength of associative links between pairs of words; it is thought to measure the automatic spread of activation from a "node" representing one word to nodes representing semantically related words. Semantic priming could thus be used to test for global alterations in the strengths of associative links across the wake-sleep cycle. Awakenings from REM and nonREM (NREM) sleep produce a period of state carry-over during which performance is altered as a result of the brain's slow transition to full wakefulness, and cognitive testing in this period can provide information about the functioning of the brain during the prior sleep period. When subjects were tested across the night - before and after a night's sleep as well as immediately following forced awakenings from REM and NREM sleep-weak priming (e.g., thief-wrong) was found to be state dependent (p = 0.016), whereas strong priming (e.g., hot-cold) was not (p = 0.89). Weak primes were most effective in the presleep and REM sleep conditions and least effective in NREM and postsleep conditions. Most striking are analyses comparing weak and strong priming within each wake-sleep state. Contrary to the normal pattern of priming, subjects awakened from REM sleep showed greater priming by weak primes than by strong primes (p = 0.01). This result was seen in each of three protocols. In contrast, strong priming exceeded weak priming in NREM sleep. The shift in weak priming seen after REM sleep awakenings suggests that cognition during REM sleep is qualitatively different from that of waking and NREM sleep and may reflect a shift in associative memory systems, a shift that we hypothesize underlies the bizarre and hyperassociative character of REMsleep dreaming. Known changes in brainstem activity that control the transition into and maintenance of REM sleep provide a possible explanation of this shift.

Sleep-Induced Changes in Associative Memory

Cellular and molecular connections between sleep and synaptic plasticity.

We analyzed the electrical activity of the basolateral amygdala (BLA), anterior and posterior regions of the cingulate gyrus (A-CG and P-CG), the dorsal hippocampus (DH), the anterior ventral thalamic nucleus (AVTN), and the sensory motor cortex during the rapid eye movements and ponto-geniculo-occipital (PGO) activity of REM sleep in cats in chronic preparation. Polygraphic recordings and computational perievent averages using the phasic contractions of the lateral rectus muscle (LR) of the eyeball as the triggering signal of the analysis were performed. We observed biphasic potentials (200-300 ms) of variable amplitude, related to the phasic phenomena of REM sleep, in the BLA, A-CG, P-CG, DH, and AVTN. The latencies of the potentials of these regions were always greater than those of the geniculate PGO activities. We propose that the recorded limbic potentials resulted from propagation of PGO activity and that this phenomenon may reflect the limbic structure of the hallucinatory, vegetative, and emotional components of REM sleep.

/pdf/phasic-activity-of-the-basolateral-amygdala-cingulate-gyrus-3vw7qyw3my.pdf

J M Calvo

Papers

Phasic Activity of the Basolateral Amygdala, Cingulate Gyrus, and Hippocampus During REM Sleep in the Cat