As mentioned earlier, REM sleep is marked by rapid movements of the eyes. The brain waves associated with this stage of sleep are very similar to those observed when a person is awake, as shown in Figure \(\PageIndex{1}\), and this is the period of sleep in which dreaming occurs. It is also associated with paralysis of muscle systems in the body with the exception of those that make circulation and respiration possible. Therefore, no movement of voluntary muscles occurs during REM sleep in a normal individual; REM sleep is often referred to as paradoxical sleep because of this combination of high brain activity and lack of muscle tone. Like NREM sleep, REM has been implicated in various aspects of learning and memory (Wagner et al., 2001), although there is disagreement within the scientific community about how important both NREM and REM sleep are for normal learning and memory (Siegel, 2001).
Figure \(\PageIndex{1}\): (a) A period of rapid eye movement is marked by the short red line segment. The brain waves associated with REM sleep, outlined in the red box in (a), look very similar to those seen (b) during wakefulness. [“Figure 4.12”/OpenStax is licensed under CC BY 4.0.]
If people are deprived of REM sleep and then allowed to sleep without disturbance, they will spend more time in REM sleep in what would appear to be an effort to recoup the lost time in REM. This is known as the REM rebound, and it suggests that REM sleep is also homeostatically regulated. Aside from the role that REM sleep may play in processes related to learning and memory, REM sleep may also be involved in emotional processing and regulation. In such instances, REM rebound may actually represent an adaptive response to stress in nondepressed individuals by suppressing the emotional salience of aversive events that occurred in wakefulness (Suchecki et al., 2012).
While sleep deprivation in general is associated with a number of negative consequences (Brown, 2012), the con- sequences of REM deprivation appear to be less profound (as discussed in Siegel, 2001). In fact, some have suggested that REM deprivation can actually be beneficial in some circumstances. For instance, REM sleep deprivation has been demonstrated to improve symptoms of people suffering from major depression, and many effective antidepressant medications suppress REM sleep (Riemann et al., 2001; Vogel, 1975).
It should be pointed out that some reviews of the literature challenge this finding, suggesting that sleep deprivation that is not limited to REM sleep is just as effective or more effective at alleviating depressive symptoms among some patients suffering from depression. In either case, why sleep deprivation improves the mood of some patients is not entirely understood (Giedke & Schwärzler, 2002). Recently, however, some have suggested that sleep deprivation might change emotional processing so that various stimuli are more likely to be perceived as positive in nature (Gujar et al., 2011).
The hypnogram below (Figure \(\PageIndex{2}\)) shows a person’s passage through the stages of sleep.
Figure \(\PageIndex{2}\): A hypnogram is a diagram of the stages of sleep as they occur during a period of sleep. This hypnogram illustrates how an individual moves through the various stages of sleep. [“Figure 4.13”/OpenStax is licensed under CC BY 4.0.]
LINK TO LEARNING
View this video that describes the various stages of sleep.
Dreams
The meaning of dreams varies across different cultures and periods of time. By the late nineteenth century, German psychiatrist Sigmund Freud had become convinced that dreams represented an opportunity to gain access to the unconscious. By analyzing dreams, Freud thought people could increase self-awareness and gain valuable insight to help them deal with the problems they faced in their lives. Freud made distinctions between the manifest content and the latent content of dreams. Manifest content is the actual content, or storyline, of a dream. Latent content, on the other hand, refers to the hidden meaning of a dream. For instance, if a woman dreams about being chased by a snake, Freud might have argued that this represents the woman’s fear of sexual intimacy, with the snake serving as a symbol of a man’s penis.
Freud was not the only theorist to focus on the content of dreams. The twentieth century Swiss psychiatrist Carl Jung believed that dreams allowed us to tap into the collective unconscious. The collective unconscious, as described by Jung, is a theoretical repository of information he believed to be shared by everyone. According to Jung, certain symbols in dreams reflected universal archetypes with meanings that are similar for all people regardless of culture or location.
The sleep and dreaming researcher Rosalind Cartwright, however, believes that dreams simply reflect life events that are important to the dreamer. Unlike Freud and Jung, Cart- wright’s ideas about dreaming have found empirical support. For example, she and her colleagues published a study in which women going through divorce were asked several times over a five-month period to report the degree to which their former spouses were on their minds. These same women were awakened during REM sleep in order to provide a detailed account of their dream content. There was a significant positive correlation between the degree to which women thought about their former spouses during waking hours and the number of times their former spouses appeared as characters in their dreams (Cartwright et al., 2006). Recent research (Horikawa et al., 2013) has uncovered new techniques by which researchers may effectively detect and classify the visual images that occur during dreaming by using fMRI for neural measurement of brain activity patterns, opening the way for additional research in this area.
Recently, neuroscientists have also become interested in understanding why we dream. For example, John Hob- son (2009) suggests that dreaming may represent a state of protoconsciousness. In other words, dreaming involves constructing a virtual reality in our heads that we might use to help us during wakefulness. Among a variety of neurobiological evidence, Hobson cites research on lucid dreams as an opportunity to better understand dreaming in general. Lucid dreams are dreams in which certain aspects of wakefulness are maintained during a dream state. In a lucid dream, a per- son becomes aware of the fact that they are dreaming, and as such, they can control the dream’s content (LaBerge, 1990).
REFERENCES
Brown, L. K. (2012). Can sleep deprivation studies explain why human adults sleep? Current Opinion in Pulmonary Medicine, 18, 541–545. doi.org/10.1097/MCP.0b013e3283596740
Cartwright, R., Agargun, M. Y., Kirkby, J., & Friedman, J. K. (2006). Relation of dreams to waking concerns. Psychiatry Research, 141, 261–270. https://doi.org/10.1016/j.psychres.2005.05.013
Fogel, S. M., & Smith, C. T. (2011). The function of the sleep spindle: A physiological index of intelligence and a mechanism for sleep- dependent memory consolidation. Neuroscience & Biobehavioral Reviews, 35, 1154–1165. doi.org/10.1016/j.neubiorev. 2010.12.003
Giedke, H., & Schwärzler, F. (2002). Therapeutic use of sleep deprivation in depression. Sleep Medicine Reviews, 6, 361–377. https://doi.org/ 10.1053/smrv.2002.0235
Gujar, N., Yoo, S., Hu, P., & Walker, M. P. (2011). Sleep deprivation amplifies reactivity of brain reward networks, biasing the appraisal of positive emotional experiences. Journal of Neuroscience, 31, 4466–4474. https://doi.org/10.1523/JNEUROSCI.3220-10.2011
Halász, P. (1993). Arousals without awakening—Dynamic aspect of sleep. Physiology & Behavior, 54, 795–802. doi.org/10.1016/ 0031-9384(93)90094-V
Hobson, J. A. (2009). REM sleep and dreaming: Towards a theory of protoconsciousness. Nature Reviews Neuroscience, 10, 803–814. https://doi.org/10.1038/nrn2716
Horikawa, T., Tamaki, M., Miyawaki, Y., & Kamitani, Y. (2013). Neural decoding of visual imagery during sleep. Science, 340(6132), 639–642. https://doi.org/10.1126/science.1234330
LaBerge, S. (1990). Lucid dreaming: Psychophysiological studies of consciousness during REM sleep. In R. R. Bootzen, J. F. Kihlstrom, & D. L. Schacter (Eds.), Sleep and cognition (pp. 109–126). American Psychological Association.
Poe, G. R., Walsh, C. M., & Bjorness, T. E. (2010). Cognitive neuroscience of sleep. Progress in Brain Research, 185, 1–19. https://doi.org/ 10.1016/B978-0-444-53702-7.00001-4
Riemann, D., Berger, M., & Volderholzer, U. (2001). Sleep and depression—Results from psychobiological studies: An overview. Biological Psychology, 57, 67–103. doi.org/10.1016/ S0301-0511(01)00090-4
Steriade, M., & Amzica, F. (1998). Slow sleep oscillation, rhythmic K-complexes, and their paroxysmal developments. Journal of Sleep Research, 7(1 Suppl.), 30–35. doi.org/10.1046/ j.1365-2869.7.s1.4.x
Stone, K. C., Taylor, D. J., McCrae, C. S., Kalsekar, A., & Lichstein, K. L. (2008). Nonrestorative sleep. Sleep Medicine Reviews, 12, 275–288. https://doi.org/10.1016/j.smrv.2007.12.002
Suchecki, D., Tiba, P. A., & Machado, R. B. (2012). REM sleep rebound as an adaptive response to stressful situations. Frontiers in Neuroscience, 3, 1–12. https://doi.org/10.3389/fneur.2012.00041
Vogel, G. W. (1975). A review of REM sleep deprivation. Archives of General Psychiatry, 32, 749–761. doi.org/10.1001/ archpsyc.1975.01760240077006
Wagner, U., Gais, S., & Born, J. (2001). Emotional memory formation is enhanced across sleep intervals with high amounts of rapid eye movement sleep. Learning & Memory, 8, 112–119. doi. org/10.1101/lm.36801
