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Why Do We 'See Stars'?

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 Biology   |   Health   |   Science
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When you bash your head and “see stars,” what’s going on? Why does your brain pick this moment to give you a laser light show? Josh explains the phenomenon of seeing stars in this Brainstuff video.

Learn more at HowStuffWorks.com

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Hey there. I'm Josh Clark and this is BrainStuff, and this is the BrainStuff where I talk to you about seeing stars.

So have you ever seen some lights appear in your field of vision? And you were kind of certain they weren't really there?And instead of coming closer and eventually landing and kicking off a really weird experience where you ended up abducted and probed and then dumped in the woods... that didn't happen?

And instead these lights went away, they were probably phantoms? Well then you, my friend, saw what are called 'phosphenes.'

Phosphenes are lights that aren't really there. They're the result of your visual system being fooled in some shape or fashion. And your visual system itself consists of about three main parts.

You've got your retina, which are the light sensitive cells in the back of your eye that pick up photons from the environment.

You've got the optic nerve, that takes the electrochemical signal that your retina translates the photons into, and carries it up to your brain.

Then you've got the occipital lobe, which is the first initial sorting center for visual stimulation.

You put all these things together and something goes from, "I see a blob of color," to "I see pizza!"

So phosphenes - again, these phantom lights - can be produced any time any part of your visual system is manipulated. And there's two main ways they can be manipulated: mechanical and electrical.

Electrical stimulation is basically where, say, you take an electromagnet and run it past your occipital lobe - you can produce phosphenes. It's also been shown to produce phosphenes when you take electrodes and implant them near your optic nerve. You can actually produce phosphenes in people who are blind because of a retinal malfunction. That means that the rest of their visual system is working, and if you stimulate it electrically, you can produce these phantom lights. Which is pretty awesome.

There's also mechanical stimulation, which is like when your rub your eyes like Tom or Jerry. You can also produce it when you press the side of your eye very gently and slowly toward your nose. It will eventually produce phosphenes. You can go ahead and do it - just do it gently.

Mechanical stimulation can also be induced in the occipital lobe itself, specifically if somebody hits you over the back of your head with a guitar and your brain slaps around your skull in that area. The neurons, stimulated suddenly, are fooled into thinking that they are sensing something, and maybe getting an electrochemical signal from the optic nerve.

You can also see stars from things like sneezing, which is pressure induced, kind of like pressing on your eye. There's also something that has to do with blood pressure, although it's not quite clear why. Where if you stand up quickly, you feel a little faint and you start to see stars? It's probably from a change in the oxygen available to either your retinal cells, optic nerve, or your neurons.

And there's other ways phosphenes can be produced too, like, for example, drugs. Or if you lack any kind of visual stimulation, like you're a long distance trucker or a pilot flying at night. You can start to hallucinate phosphenes.

So should you be worried if you see stars? Well, if you've just been pressing your eye or you just sneezed and the stars come and go pretty quickly, probably not.

But if somebody did hit you over the back of the head and you're seeing stars, you should probably go to the ER, because you may have just suffered a concussion.

And if you're walking around and inexplicably see phosphenes all the time, you should also go to the doctor, because you may have some sort of underlying medical condition.

But for the most part, phosphenes are just kinda cool and not really problematic.

SOURCES:

http://www.thenakedscientists.com/HTM...

http://gizmodo.com/5845124/why-do-you...

http://www.sciencedirect.com/science/...

http://www.ncbi.nlm.nih.gov/pubmed/16...

http://www.ncbi.nlm.nih.gov/pubmed/15...

http://www.ncbi.nlm.nih.gov/pubmed/21...

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