Livewired Brain #2: Dream Theory

In an earlier blog, we saw how the brain changes both its hardware and software. And how quickly it can do that. In Livewired, David Eagleman elaborates on his theory for an age-old question: Why do we dream?

 

The basis of his theory is the speed at which the brain can rewire itself. (Remember, from the last blog, blindfolded people started using their “sight” areas of the brain for “touch” activities within 40-60 minutes). If that is how fast the brain can rewire itself, well, the visual cortex has a major problem unlike the sound, or touch areas of the brain. How does the visual cortex prevent itself from being taken over by the other parts of the brain, given that the world is dark half the time, thanks to that pesky thing called rotation? (Electricity is a very recent invention, in evolutionary terms).

 

The answer his team has proposed?

“By keeping the occipital cortex active during the night. We suggest that dreaming exists to keep the visual cortex from being taken over by neighboring areas.”

 

Ok, that’s a possibility, but a good theory should align and explain other facts, preferably facts that it wasn’t designed to explain. How does this theory fare on those fronts? Eagleman explores.

 

Well, for one, we dream visually, i.e., our dreams are “pictorial and filmic”. That certainly aligns with the aim of keeping the visual cortex “busy” at night. How about blind people? It turns out blind-from-birth people have non-visual dreams. After all, if no part of the brain was ever “assigned” for sight, those signals to the brain that correspond to dreaming would be interpreted based on what that visual cortex is being used for in blind people. Usually touch. And yes, blind-from-birth people have tactile dreams, not visual ones.

 

We can’t remember most of our dreams. This too aligns with the theory. If the purpose is only to prevent the visual cortex from being taken over, well, why waste energy on “writing” the dream into memory?

 

Eagleman next looks at other species. But first, a quick reminder that the time of dreaming is called REM sleep (Rapid Eye Movement). Species born helpless (like humans, platypuses, ferrets) need a lot of rewiring of the brain, and all these species have a lot more REM sleep than those species that hit the ground running at birth (the brains of those species are obviously more mature at birth, but also they have limited ability to adapt or learn).

“In our interpretation, when a highly plastic brain drops into the world, it needs to constantly fight to keep things balanced. When a brain arrives mostly solidified, there is less need for it to engage in nighttime fighting.”

 

And lastly, the older we get, the less plastic our brains become. And that correlates with the fact that older folks dream less than younger ones who in turn dream far less than babies.

 

To sign off on the theory, like any good scientist, he makes a couple of (half-serious, half-joking) predictions based on his theory. First, if we ever find life on another planet which is locked into place (i.e., one side always facing its sun/star), well, species on the sun-facing side shouldn’t have any use of dreaming. Second, if the night time on any such planet is shorter than the time it takes to rewire the brain, then any species on those planets wouldn’t need to dream either.

“Thousands of years hence, we might finally know whether we dreamers are in the universal minority.”