MadSci Network: Neuroscience Query:

Thank-you very much for this most intriguing question. I am sorry it took me so long to respond, but despite an exhaustive search, I have been unable to find any research related to your question. However, for readers who may have never heard of phosphenes, I am going to present a brief description of this phenomena, and in the end, I will present my own opinion of why it prompts you to fall asleep. Most of the information below about phosphenes is based on a publication by Suzanne Carr and other information I have found on the Internet. The Carr reference and a few others are given below. It has been widely reported that prisoners confined to dark cells often see brilliant light displays, which is sometimes called the ``prisoner's cinema.'' Truck drivers also see such displays after staring at snow- covered roads for long periods, and pilots may experience phosphenes, especially when they are flying alone at high altitudes with a cloudless sky. In fact, whenever there is a lack of external stimuli, these displays can appear. They can also be made at will by simply pressing your fingertips against closed eyelids. In addition, they can also be produced by an electrical shock. In fact, reportedly, it was high fashion in the eighteenth century to have a phosphene party. It is noted that Benjamin Franklin once took part in such an encounter where a circle of people holding hands would be shocked by a high-voltage electrostatic generator, so that phosphenes were created each time the circuit was completed or broken. The earliest account of phosphenes is given by the Bohemian physiologist Johannes Purkinje in 1819. These subjective images are called phosphenes (from the Greek phos, light, and phainein, to show). Oster (1970) suggests that, because phosphenes originate within the eye and the brain, they are a perceptual phenomenon common to all mankind. The visual areas of the brain at the back of the head (occipital lobe) can also be stimulated to produce phosphenes. In regards to your question, I have never heard of the feedback loop you describe whereby viewing phosphenes would lead to a sleep state, nor have I been able to find any research on it. The brain contains many (perhaps an infinite number) of feedback loops. One of these involves a pathway between a part of the frontal lobe of the brain, which extends through the cingulate gyrus, caudate nucleus and down to the thalamus. This particular pathway is associated with the neurotransmitter serotonin, which is involved in many biological processes, including those of depression and sleep, and has been associated with the disorder called obsessive-compulsive disorder. Some people speculate that this particular pathway may also be active (or perhaps too active) in people who have problems falling asleep. So perhaps watching phosephenes may help calm down or de-activate this particular system. Another part of the brain that may be involved is the reticular activating system which is involved with arousal and sleep. These may be interesting areas for you to pursue. However, I would not entirely give up on the notion that the reason you fall asleep is due to relaxation or self- hypnosis. For example, watching phoshenes may help clear your mind of distractions that keep you awake. Similarly, this intense type of focusing is not unsimilar to various methods used for meditation. In any event, I am sorry that I cannot give you a direct answer to your question, but I encourage you to keep searching! Here are some sources of information that you can pursue. http://elf.gi.alaska.edu/~physics/19961997/phosphene.html

http://www.oubliette.zetnet.co.uk/Three.html (Suzanne Carr)

http://www.phosphenism.com/uk/stasupuk.html

Oster, G. 1970. Phosphenes. Scientific American:222(2):83-87 Walker, J. 1981. The Amateur Scientist: About Phosphenes: patterns that appear when the eyes are closed. Scientific American 244:142-52.

MadSci Network, webadmin@www.madsci.org

© 1995-2000. All rights reserved.