Perception is a weird thing. We tend to think of our sensory organs—eyes, ears, nose, skin, tongue—as windows to the outside world. But they're not windows, they're sensors and that makes a big difference. Our senses don't let in an unfiltered reality, but rather process incoming data and send signals to the brain which then constructs an experience that should, in theory, accurately represent the outside world. When you see a flower, you're really seeing a reconstruction of a flower that your quantum meat-computer put together based on incoming optical data. When things go wrong on this path from optical sensor (eyeball) to quantum meat-computer (brain) and bogus data is interpreted as real, we see things that aren't there: hallucinations. A new study has found that the mammalian brain is far more susceptible to bogus data than previously thought, and it raises an intriguing mystery. Based on the results of this study, there's enough noise in our systems of perception that we should constantly be hallucinating, and it is a mystery that we have any sort of agreed upon reality at all.
Karl Deisseroth, a neuroscientist and psychiatrist at Stanford University who lead the study says:
"Back in 2012, we had described the ability to control the activity of individually selected neurons in an awake, alert animal. Now, for the first time, we've been able to advance this capability to control multiple individually specified cells at once, and make an animal perceive something specific that in fact is not really there -- and behave accordingly."
The study, published in the journal Science, consisted of cutting windows into mice's brain and hitting the brain with lasers to induce hallucinations. Which is weird and cruel, but hey that's science for you. You have to crack a few brains to make a hallucinatory mouse-omelet. The researchers found that although mouse brains have millions of neurons, they only needed to hit approximately 20 individual neurons with the laser to make the mouse see a pattern that wasn't there.
The induced hallucinations themselves were fairly simple. The researchers trained the mice to react differently to being shown vertical lines or horizontal lines projected on a wall. When shown vertical lines the mice were trained to lick a water bottle. The mice were shown "real" projections of these horizontal or vertical lines, and the researchers recorded which neurons fired in response to the specific pattern. They then targeted those specific neurons with lasers, and the mice reacted in the same exact way as they had been trained, as if they were seeing the patterns actually projected onto the wall. When the neurons that reacted to the vertical pattern were activated, the mice licked the water bottle and when the horizontal neurons were targeted, they did not. According to Deisseroth:
"A mouse brain has millions of neurons; a human brain has many billions. If just 20 or so can create a perception, then why are we not hallucinating all the time, due to spurious random activity? Our study shows that the mammalian cortex is somehow poised to be responsive to an amazingly low number of cells without causing spurious perceptions in response to noise."
It's less than comforting to think that our brains have to be so finely tuned to keep us from constantly hallucinating. Finely tuned machines have a way of breaking catastrophically—it's easier to keep a broken 4-cylinder Toyota on the road than it is a broken Lamborghini. Even less comforting is this: according to the press release, this research was funded in part by the Defense Advanced Research Projects Agency. So, yeah, there's that too. Sleep tight.