Score another one for unconscious processing, which is especially prevalent during sleep. A new study in PNAS suggests that, as people sleep, their brains are forming relational memories, which require “the flexible ability to generalize across existing stores of information”.
Earlier studies found that people appear better able to remember things they have just learned if they are able to sleep soon after. In effect, they found, the brain appears to use sleep time to consolidate memories.
This study suggests that the process is still more complex, and that sleep helps people make inferences from bits of knowledge that may at first appear random, said one of the authors, Dr. Jeffrey M. Ellenbogen of Brigham and Women’s Hospital, the Harvard affiliate.
People make minor inferences all the time without sleeping first, of course, but those connections tend to be fairly straightforward. Sleep appears to play a role in helping people make “big picture” realizations, Dr. Ellenbogen said, like those involved in major scientific breakthroughs.
This elegant little study builds on a bevy of recent research. Last year, Ap Dijksterhuis published a paper in Science demonstrating that people often make better shopping decisions, at least when it comes to complex products, when they rely on their unconscious brain. Instead of consciously analyzing all of their options, consumers were most effective when they practiced “deliberation without attention,” and let their unconscious brain digest the information while they were busy doing something else, like watching television or sleeping. Dijksterhuis summarizes the implications of his research:
Use your conscious mind to acquire all the information you need for making a decision–but don’t try to analyze the information. Instead, go on holiday while your unconscious mind digests it for a day or two. Whatever your intuition then tells you is almost certainly going to be the best choice.
While a rat was running through a variety of different mazes, Wilson measured clusters of neurons in the hippocampus with multiple electrodes surgically implanted in its brain. As he’d hypothesized, Wilson found that each maze produced its own pattern of neural firing. To figure out how dreams relate to experience, Wilson recorded input from these same electrodes while the rats were sleeping. He was astonished by his results. Of the 45 rat dreams recorded by Wilson, 20 contained an exact replica of the maze they had run earlier that day. “During REM sleep, we could literally see these rat brains relive minutes of their previous experience,” Wilson says. “It was like they were watching a movie of what they had just done.”
But why would rats dream of running through a maze again? What’s the advantage of replaying the activities of the day at night? According to Wilson, dreaming is a form of mental cleaning. The brain is figuring out what information it needs to keep. Since Wilson rewarded the successful rats with food, their brains were re-encoding the route, making sure they remembered how to find their way.
The moral of these studies is simple: the unconscious brain is our own personal supercomputer. While our consciousness can only process about 40 bits of information per second, the unconscious can process several million bits per second. As a result, it plays an essential role in helping us learn new information and properly assimilate it into our existing store of knowledge. It also happens to work best at night. It’s ironic, but true: some of our best thinking is done while sleeping.