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Rewiring happens after you stop
After a bout of intense focus, the circuits highlighted by acetylcholine strengthen during sleep that night and the following nights, and others are lost. Acetylcholine marks those synapses neurochemically and metabolically, so they are more biased to change. After a poor night's sleep, the learning can still happen on the next night or the one after. Without deep sleep, those changes probably won't come.
A paper in Cell Reports tested a hard spatial memory task: remembering a sequence of lights, from a few up to 15 or 16. People who took a 20 minute Non Sleep Deep Rest protocol, or a shallow nap lying down with eyes closed and no sensory input, right after the task learned significantly more than people who had only a good night's sleep.
Walking, running, and cycling work as another kind of rest. Self-generated optic flow, with the world floating past the retina, shuts down areas like the amygdala that release epinephrine and create alertness. Letting the mind drift after deliberate effort is one way to speed learning.
Why does sleep strengthen new learning?
During deep sleep, the hippocampus replays patterns of activity from the day, and the cortex takes on the memory as a lasting trace. Matthew Wilson's lab at MIT recorded this replay in rats in 1994, finding that cells active in a maze fired in the same order during later sleep. Slow oscillations in the cortex coordinate this transfer. Sleep spindles, brief bursts of activity, are linked to how well it works.
What does optic flow do to the brain?
Optic flow is the pattern of motion across the retina as we move through the world. Researchers have found that it engages areas that track movement and position, and that moving through an environment can ease activity in threat circuits. Walking, running, and cycling all produce it. The amygdala, which helps drive alertness, is part of those circuits.
How long is a nap's effect on memory?
Studies by Sara Mednick at the University of California, Riverside found that naps containing slow wave sleep improved performance on a visual learning task. Even a short rest period can boost memory for material studied just beforehand, according to work by Michaela Dewar and colleagues at Heriot-Watt University. Their volunteers rested in a quiet room for ten minutes after hearing stories and recalled more later. The rest period quieted new input and gave the brain time to consolidate.
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