We’ve all had the night-before-a-big-day anxiety dream and have our own interpretation of what that dream meant to us, but how exactly do we dream? While there is still very little known about the precise neurophysiology involved in dreaming, recent advances in science- such as the development of electroencephalography (EEG)- have lead us closer than ever to understanding not only why we dream, but also how.
Up until about 60 years ago sleep was thought to be a period of complete inactivity for the brain. We now know that the brain can sometimes be even more active during REM sleep than during wakefulness. REM, or rapid eye movement, is the stage of sleep that most physiologists and psychologists agree is the main period during which we dream. REM sleep is characterized not only by an increase in brain activity, but also fluctuating heart and respiratory rates, and a slight decrease in overall body temperature. On the other hand, non-REM sleep comprises much of our time spent asleep. It is characterized by a decrease in heart and respiratory rates and an overall decrease in brain activity compared to our active state.
So what exactly is our body doing while we sleep? The decrease in temperature that occurs while we sleep may be easily explained by a fundamental need to conserve energy. Many sleep researchers even believe that a primary function of sleeping is to conserve energy that would normally be used towards maintaining body temperature and other physiological functions. But, there are several different sleep theories- and since they are theories, no one knows for sure which, if any, are correct.
One thing we do know is that, as far as physiological processes go, many things change at night while we are sleeping as compared to while we are active. Although you may think that most physiological processes would slow down at night to give our bodies a rest, there are actually many processes that peak in activity at night. In fact the release of growth hormone from the pituitary gland is much higher during sleep than during wakefulness. Other physiological activities related to digestion and cell repair also increase in activity at night, giving even more importance to getting a good night’s rest.
But what is our brain doing while we dream? A study by Dr. Athanassios Siapas from the California Institute of Technology found directional interactions in neuronal activity that resemble ripples in water. During non-REM sleep the nerve activity originates in the hippocampus then moves to the prefrontal cortex. The hippocampus is particularly important in the formation of new memories while the prefrontal cortex is important in storing memories. These distinct interactions between the hippocampus and the prefrontal cortex seem to stop completely during REM sleep, although overall brain activity is much higher than during non-REM sleep. Dr. Siapas believes that these findings show a gradual transfer of memories from the hippocampus to the prefrontal cortex during non-REM sleep, then a restructuring and reorganization of these memories during REM sleep. This theory would explain why our dreams often contain aspects of our day such as the night-before-a-big-day anxiety dream.
Dr. Robert Stickgold of Havard Medical School has also found an association with memory and sleep. When shown lists of words centered around a common theme and later asked to recall those words- subjects who recalled the words after a night of sleep were able to recall more words than those asked to recall the words later on the same day. The group asked to recall words after sleeping also showed what Stickgold calls “creative intrusions” or false recall of words that were not on the lists at all, but rather seemed to unify several lists each with drastically different themes. In fact, Stickgold tried this experiment using several different tasks such as completing a maze or finishing math problems and in all cases the group that was allowed to “sleep on it” performed much better than those who did not sleep. You can watch his TED Talk here.
While there is still much to discover in terms of the physiology of sleep and dreaming, advancements in science and modern technology offer promise for the future. You can even aid in our current understanding of sleep patterns and dreams by using the app Dream:ON which monitors your movement while you sleep and uses subtle sounds from your smartphone to influence your dreams.
Written by Talia Head
Stickgold, B. 2010. Sleep, memory and dreams: fitting the pieces together [video file]. Accessed from web Jan. 17 2015. < https://www.youtube.com/watch?v=WmRGNunPj3c>.
“The characteristics of sleep.” Healthy Sleep. Division of Sleep Medicine Harvard Medical School, 2007. Accessed from web Jan. 17 2015. <http://healthysleep.med.harvard.edu/healthy/science/what/characteristics>.
Wierzynski, C.M., E.V. Lubenov, M. Gu, and A.G. Siapas. 2009. State-dependent spike-timing relationships between hippocampal and prefrontal circuits during sleep. Neuron 61:587-596.
Wiseman, R. 2014. The dream catcher. New Scientist 221:48-50.