Panksepp explains in Affective Neuroscience that EEG recordings clearly discriminate "three global vigilance states of the nervous system—waking, SWS [slow-wave sleep], and dreaming or REM sleep." He says that in humans, there are four stages of slow-wave sleep, during which very little "active processing" takes place in the brain. Slow-wave sleep is followed, however, with a "highly activated form of sleep" involving cortical arousal, as reflected on an EEG, even more energized than the waking state. This phase of sleep is also accompanied by rapid eye movement (REM), vivid dreaming, and muscular paralysis called atonia. Panksepp discusses how it is generally believed that slow-wave sleep "reflects ongoing bodily repair processes," while REM sleep "reflects active information reintegration within the brain."
But where is VIGILANCE circuitry located? Certainly, the norepinephrine pathways from the loci coerulei to all parts of the brain are part of the VIGILANCE system (see Norepinephrine action, synthesis, and pathways). But other structures and circuits are certainly involved, such as the suprachiasmatic nuclei, which control the sleep-wake cycle. These nuclei are grouped in pairs and are situated within the hypothalamus. The image to the right, illustrating how the suprachiasmatic nuclei respond to light, is from an NIH website called "The New Genetics" and links to source.
During REM sleep, Panksepp notes that muscular twitches "break through the atonia." He writes: "During these twitches, the brain is bombarded by endogenous bolts of neural 'lightning' called PGO spikes (since they are especially evident in the visual system represented in the Pons, lateral Geniculate bodies, and Occipital cortex)." Other than the twitches during REM, the muscular atonia prevails, explains Panksepp, "because of a massive inhibition, probably induced by the amino acid transmitter glycine, exerted on the motor neurons that control the large antigravity muscles of the body."
In the illustration above left, you can see that a loud sound prompts a PGO spike (circled in red) in the lateral geniculate of a cat during non-REM sleep. This image (links to source) is from Adrian R. Morrison, "Exploring the Neurobiology of Sleep," and is originally reproduced with permission from Acta Neurobiologiae Experimentalis from Morrison and Bowker (1975). Regarding vigilance, in Morrison's article, he tells an interesting story of how he came to understand that "the REM brain most resembles the awake brain when a person is on high alert."
Working with a cat lesioned in the area of the brain responsible for atonia, within the pons, Morrison and a student, Robert Bowker, observed that the cat flinched at an unexpected loud sound but without waking up. In other words, the cat's brain had an alerting response and since the usual atonia of REM had been disabled so to speak, the cat had a muscular reaction—a flinch. There was also an accompanying PGO spike on the EEG. Through his reading and research, since PGO spikes characterize REM sleep, Morrison has come to conclude that the alerting response is ultimately responsible for atonia. His story illustrates how he came to the conclusion that just at the moment when we are alerted to a source of danger—for example a car in our peripheral vision as we are about to cross the street—we experience a hitch in our step, a slight hesitation, what Morrison believes is a moment of atonia. And REM, he theorizes, is a long bout of alerting responses which produce atonia.
One way many animals survive in the wild is to "freeze" when they see or smell a predator in the distance so as not to attract attention with movement. Perhaps this "freezing" is the kind of atonia to which Morrison refers. On an Indiana Public Media site, in "Freeze!," Don Glass writes: "The reason an ability to freeze works as a defense is that a predator's attack behavior may actually be triggered by motion. A frog, for example, will literally starve to death in a box full of dead flies. Pass one of those flies in front of its eyes on a little string, though, and it will automatically gulp it down." Glass goes on to say "The response to freeze is completely hard-wired, so freezing shows us something about both predator and prey. Evolution has caused the freeze strategy to come into existence precisely because it fits in with the way the visual systems of predators operate."
In healthy individuals, the PGO spikes that characterize an alerting response do not occur during normal waking states. Panksepp points out, however, that in schizophrenic patients, such "electrical events have been recorded from deep limbic areas." He points out that the only other times this electrical signature has been observed during a waking state have been when a subject is "under the influence of LSD" or with complex chemical manipulations. Regarding schizophrenia, which we know somehow involves excessive dopamine transmission, Panksepp writes: "When these systems become overactive, our imagination outstrips the constraints of reality. We begin to see causality where there are only correlations."
S.M. Trbovic, in "Schizophrenia as a possible dysfunction of the suprachiasmatic nucleus" (2009), writes: "Psychosis and dreaming have many similarities, including delusions, hallucinations, bizarre thinking and perceptual distortions." Trbovic points out that schizophrenic patients "have certain sleep architecture characteristics, and distinctive biological markers suggesting abnormity of the SCN, including irregular pattern of melatonin secretion, abnormal actigraphyic studies, D1-dopamine receptors involvement in the process of entraining the SCN [suprachiasmatic nuclei] and vulnerability to psychotic exacerbation due to jet lag." It is interesting that Trbovic is interested in the role of dopamine receptors in "entraining" the suprachiasmatic nuclei since bright light normally entrains or synchronizes these structures.
Trbovic also calls attention to the influenza virus, explaining that the virus "has been implicated in the etiology of schizophrenia," and "is capable of resetting" the suprachiasmatic nuclei. Previously in CorticalBrain.com, we discuss the role of the influenza virus in postencephalitic disorders (see Encephalitis, OCD symptoms, and Parkinsonism. In Part 3 of CorticalBrain.com, we will discuss the role of infection in obsessive-compulsive disorder.
Dopamine and dreaming in REM sleep:
The image to the right depicting the stages of sleep as recorded during polysomnography is from a Department of Respiratory Care Education website, Kansas Medical Center, and links to source. Regarding norepinephrine and serotonin systems, Panksepp discusses how these systems "exhibit their highest levels of activity during waking," slow down during slow-wave sleep and "a few moments prior to REM they cease firing." He goes on to say: "In short, they are inactive during dreaming." On the other hand, other than the bursts of firing that occur when animals seek rewards, Panksepp points out that dopamine neurons fire at a steady rate throughout waking, slow-wave sleep, and REM sleep.
Panksepp explains that "prefrontal areas, which generate active plans, remain quiescent" during both slow-wave sleep and REM sleep. In contrast, "PET scan images of the brain during dreaming highlight clear arousal in the limbic system, especially the amygdala." Also, the hippocampi exhibit a highly synchronous theta rhythm during REM sleep. Panksepp notes that this type of hippocampal synchronization "is common when animals are exploring their environment" and "usually indicates that the circuits are systematically encoding information (i.e., translating recent experiences into long-term memories)." As an example, he reports that "in olfactory creatures such as rats there is a lot of whisker twitching and sniffing" during REM sleep, behaviors that are "normally seen during exploration of the environment and investigation of objects." As we discuss in The Brain's SEEKING System, it is dopamine that prompts exploratory activity. So even during sleep, the SEEKING system—running primarily on dopamine—remains ready for action.Next-> Hypervigilance, depression, obsessions, and compulsions:
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