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In Brief
- Some animals sense light with organs outside their eyes, but humans do not. Still, some blind people can adjust their body to the cycle of night and day.
- In recent years such nonvisual responses to light have been linked to specialized neurons in the retina that can detect light autonomously but also relay signals from rods and cones, other light-sensing cells.
- These neurons respond to blue light and may be remnants of evolutionarily ancient organs from our invertebrate past.
- The discovery may lead to new approaches to treating seasonal affective disorder, certain sleep disorders and other debilitating conditions.
In the 1920s Harvard University graduate student Clyde E. Keeler discovered two surprising facts about mice he had bred in his rented attic room. One, all the progeny were completely blind. Two, despite the animals’ blindness, their pupils still constricted in response to ambient light, albeit at a slower rate than did the pupils of sighted mice.
Many years later researchers extended Keeler’s observation, showing that mice genetically engineered to lack rods and cones (the light receptors involved in vision) nonetheless reacted to changes in light by adjusting their circadian clock—the internal timer that synchronizes hormone activity, body temperature and sleep. The animals performed the usual daytime activities when in daylight and nighttime activities when in the dark. They could do so even though their retinas lacked the photoreceptor cells that vertebrate eyes use to form images, although surgically removing their eyes abolished this ability. This phenomenon may be common to many mammals, including humans: recent experiments have shown that certain blind people can also adjust their circadian clocks and constrict their pupils in response to light.
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8 Comments
Add CommentHow frustrating! An interesting report with absolutely no references or even names of the researchers that "extended Keeler's observation". Please update the article with some references. Links off to other articles on animals or sleep are not helpful. Please use reasonable standards of scientific reporting.
Reply | Report Abuse | Link to thisJeez! One would think that SA could have blogs that don't allow spammers. Other blogs don't have such bilge in them.
Reply | Report Abuse | Link to thisXristy...You are right on about the spamming... I am so tired of the SA spam which I too don't see on other blogs... SA needs to lay some security into place or increase the number of moderators. Seeing this stuff all over the place is disheartening. Looks like SA needs to step up and take a more responsible approach to its audience... This stuff makes Scientific American cheezy if they can't be bothered to clean it up faster or stop it. It's not up to the reader, it's up to SA to deal with the SpamHeads.
Reply | Report Abuse | Link to thisMore please! For instance I have had extensive surgery on both eyes (detached retinas and recently cataract surgery) would this have affected this 'hidden organ'? As it is located in the retina (apparently) my guess is probably yes, if so, how? Would this account for disturbed sleep patterns etc?
Reply | Report Abuse | Link to thisThis article is referring to the melanopsin system, which includes retinal ganglion neurons which are directly sensitive to light (rather than just relaying light detection from the rods and cones). It feeds day-length-related information to the hypothalamus, essential to sleep cycle regulation, using the neurotransmitter melanopsin.
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Melanopsin is a good place to start.
I believe the article is in the print issue, as stated above.
Reply | Report Abuse | Link to thisAll references no doubt follow the actual article.
You reached this webpage through a link subtitled as "preview."
Sensory organs were so useful for animals (as well as other organisms, and quite early) that, as the "in Brief" notes state, they developed early in evolution.
Neurons are cells specialized in sensing (communication involves reception of information - Gregory Bateson called information, "a difference that makes a difference"). Doubtless neurons evolved in the same way as other differentiated cells, through variable expression of genes that began by coding for chemical-detecting proteins/enzymes in unicellular organisms.
Prokaryotes, too, possess capacity for detection of, and communication with a constantly varying environment.
Life itself may be simply described as interaction in this way.
The brains you're using are an elaboration of this magnificent invention and process: chemistry! (and you wondered why you liked me. . .)
I am trying out the sleepwell specs to get my circadian rhythm back in order as I have been having trouble sleeping for the last year. I'll report back with results. The glasses are fitted with filtered CR39 lenses which completely remove the blue wavelengths of light to prevent them from reaching the retina. They were quite pricey and I am happy with the build. Website is here:
Reply | Report Abuse | Link to thishttp://www.sleepwellspecs.com/
I agree with xristy. Please include relevant links and research information for further information when you post an article. I am surprised at how little substance you are including and I am disappointed.
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