Birds do it, bees do it, even educated fleas do it, and so do humans. I’m talking, of course, about sleep. We spend roughly 33% of our time on earth in semi- hibernation, with our bodies partially paralyzed and although we can’t live without it, we are still somewhat in the dark (too obvious to be intentional) about how the whole process works.
If you ask most people, they will equate sleep with rest, a recharging of the ol’ battery. If you ask neuroscientists about sleep, they will tell you that it’s some of the brain's most important working hours, when memory is consolidated and strengthened.
In our waking state, we take in a vast amount of information through our five senses. Hebb's rule says, “ synapses that fire together, wire together.” This is known as synapse potentiation, the idea that synapses, the chemical/electrical wiring connectors in our brains, lock in memory through the frequent friending of other synapses. This in a nutshell is what happens when you experience an act of learning.
The thought is that during sleep, your brain goes over and reviews all your waking memories of learning, underscoring and reinforcing them. Your memories serve as the reference points for decision-making. Since one bad decision can prove fatal, sleep, even narrowly defined under these parameters, is essential to survival.
That’s the conventional wisdom, but what about unconventional wisdom? In science, it seems that it is often the weird stuff that eventually ends up having its day in the sun. (Or at least the stuff we like to write about.)
Enter scientists Giulio Tononi, and Chiara Cirelli from the University of Wisconsin-Madison. In a Scientific American article entitled, "Perchance to Prune", they argue conventional wisdom about sleep might be fundamentally wrong.
Tononi and Cirelli postulate that it is during sleep that synapse connections actually weaken, and that this is when the brain clears out the day's accumulation of non-essential information, sort of like deleting your internet cookies so your computer runs faster.
The brain uses about 20% of our caloric intake, and 66% of that is consumed during synaptic activity. They believe that for energy efficiency, the brain restores itself to a baseline level of synapse strength during sleep. This in turn reduces the wear and tear on neurons, and allows the brain to operate properly over a normal lifetime. They call this return to baseline activity synaptic homeostasis.
The idea is that all day long you are bombarded with a ton of information, both unintentional, like witnessing a car crash, and intentional, like reading this blog. During sleep, your brain sorts through new and past memories, and reorganizes, consolidates and prunes. Tononi and Cirelli believe that it’s not so much about replaying a memory to strengthen and reinforce it as much as it’s about cutting back the dead branches to allow the rest of the synaptic tree to thrive and perpetuate in a finite energy situation. When you brain brings itself to a synaptic baseline, you're free to start each day anew, taking in a myriad of experiences, from the vital to the meaningless.
In support of this theory, they cite the fact that to date no scientific study has been able to demonstrate actual synapse potentiation (memory acquisition) during sleep.
Just what mechanism or heuristic determines what memories get stored, eliminated, repurposed, combined and consolidated? That's something Tononi and Cirelli hope to uncover.
If their theory is correct, they purport the closest you can get to this mysterious sorting process is paying attention to your dreams. Dreaming is the memory sorting process in action. The end result of that activity is one of the key elements that helps define us. In a way, you are what you sleep.
And to think it’s all done under the cover of darkness…