|MadSci Network: Neuroscience|
Dear Arun, Thank you for your interesting question about brainwave activity during sleep. Brainwave activity has been widely investigated both in awake and asleep individuals and the different activity patterns have been well characterized. Before I answer your specific question about REM sleep, allow me to briefly review what is known about brainwave activity as measured by electroencephalography (EEG). When we are awake and involved in active thinking or speaking or when we are emotionally aroused or excited, EEG records very low-amplitude (small), high-frequency (fast) brain waves. This pattern is called Beta activity. When an awake person is resting quietly, brainwaves become a little bit bigger and slower and that is known as Alpha activity, or in case of deep rest, as in meditation for example, Theta activity. Alpha and Theta activity are also observed during the first stages of sleep (1 and 2), which are short, transitory phases between wakefulness and real, "deep" sleep. As sleep becomes deeper, brainwave activity becomes much more synchronized and its shows an higher-amplitude, lower-frequency pattern that is called Delta activity. These activities define the later stages of sleep (3 and 4), which are called slow-wave sleep and which provide the most benificial rest to the sleeper. Aserinsky and Kleitman (1955) were the first to notice that about 90 minutes after the beginning of sleep, many abrupt physiological changes could be seen. More specifically, the eyes start to make "rapid eye movements" (REM), muscle tonus disseapears and the EEG reveals brainwave activity similar to that of an awake, alert individual (Beta, Alpha and/or Theta activity). This latter observation brought about the name "paradoxical sleep", as the brain seems awake while the person sleeps. This period, in which all dreams occur, lasts between 20 and 30 minutes and usually comes 4 or 5 times a night. To know more about the mechanisms that control our different sleep patterns, or about the possible roles of REM sleep, have a look at a good physiology textbook like Carlson’s Physiology and Behavior (2001), or at a specialized sleep textbook like Empson’s Sleep and Dreaming (1993). I hope this helps, Cheers Benoit References: Aserinsky, N.E. & Kleitman, N. (1955). Regularly occuring periods of eye motility and concomitant phenomena during sleep. Science, 118, 273-274. Carlson, N.R. (2001) Physiology of Behavior (7th Ed.). Boston: Allyn and Bacon. Empson, J. (1993). Sleep and Dreaming. New York: Simon and Shuster.
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