THE BLOG
02/05/2013 02:53 pm ET Updated Apr 07, 2013

Seaside Fog and Fiber-Optics: How Light Shapes Your Thoughts

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Every morning, the fog rolled in from the sea and enveloped my apartment in impenetrable gray. I'd moved into a place near the beach in the hope of enjoying some world-famous California weather -- but every day, until the sun burned away the fog around lunchtime, the only weather I saw was the thick mist that blanketed my porch. "First-world problem!" is a phrase you have every right to lob at me. Even so, the lack of sunlight was taking its toll on my personality, to the point that my friends started commenting that I seemed depressed.

When I mentioned the fog, my friends exclaimed something along the lines of "a-ha!" and clued me in to seasonal affective disorder, a form of depression that's triggered by lower-than-usual exposure to sunlight. Some sufferers -- or their employers -- combat the disorder by installing full-spectrum light bulbs or light boxes, like those made by Viva-Lite and Verilux. These devices simulate the color spectrum found in daylight, and seem to help trigger metabolic changes that counteract seasonal depression. My solution, on the other hand, was lower-tech and more expensive: I relocated to a less foggy part of town.

Light (or lack of it) affects our brains and bodies in a lot of surprising ways -- and its power can seem even weirder when neuroscientists wield it. Some experiments, for instance, suggest that shining light into a person's ears can help treat seasonal affective disorder -- while other researchers claim that looking at blue light can improve alertness.

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But when it comes light and the brain, nothing is more mind-blowing than optogenetics: The use of microscopic flashes of light -- along with light-sensitive proteins -- to control the behavior of living neurons and neural networks. Since the earliest optogenetic experiments in 2002, researchers have used targeted light bursts to isolate neural pathways involved in decision-making, to spontaneously trigger feelings of reward, and even to turn memories on and off at the flip of a switch. Scientists are also optimistic that optogenetics may soon be used to treat diseases like Parkinson's and epilepsy, as well as problems like blindness and depression.

And a new study hints that optogenetic treatments for depression may arrive even sooner than expected. A team led by Stanford's Karl Deisseroth used optogenetic techniques to pinpoint specific groups of neurons involved in depressive symptoms -- then turn those symptoms on and off at will.

As the journal Neuron reports, the scientists started by inserting fiber-optic cables into the brains of some stressed-out mice -- specifically, into each mouse's ventral tegmental area (VTA), a brain region known to play a central role in motivation and reward. Since the mice had already suffered through a day of annoyances at the hands of these scientists, they tended to lie around looking fed up -- until the researchers sent flashes of light into their VTA neurons. Suddenly, the little guys caught a second wind and started looking for escape routes from their cages. But that only lasted until the scientists optogenetically inhibited the mice's VTA pleasure circuits -- at which point the mice went right back to sulking.

Interestingly, the scientists also found that activating a mouse's reward circuits tended to increase that mouse's preference for plain water over sugar water -- while inducing depression tended to reverse that preference. I couldn't help but recall my craving for Trader Joe's chocolate chip cookies during my months in that fog-shrouded apartment.

Though you (hopefully) don't have a fiber-optic cable running into your brain, you can still use light to modify your neurons' behavior. A dose of midday sun -- or a Viva-Lite bulb -- can help alleviate depressive symptoms; and as most of us know all too well, a late night spent in front of your computer monitor can disrupt your brain's preparations for sleep. Simple facts like these are really pretty amazing when you take a second to think about them -- they demonstrate that even your inmost thoughts are tangled in ceaseless feedback loops with the world around you. And that's enough to make anyone's brain light up with curiosity.

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