While attempting to learn a new task, taking short breaks can go a long way in making it sound simple and easy, according to a new study conducted by Massachusetts Institute researchers.
Scientists David Foster and Matthew Wilson, working at the Massachusetts Institute of Technology in Cambridge, found that rats' brains 'replay' their experiences in reverse when the animals pause briefly to rest.
They suggest that eliminating such breaks could actually interfere with learning, and perhaps even explain why hyperactive children often have learning difficulties, reported the online edition of Nature.
The researchers inserted a pincushion of fine wires into the animals' skulls and monitored the electrical activity of around 100 individual brain cells in the hippocampus, a brain region involved in learning and memory.
They placed each wired-up rat in a straight 1.5-metre run. They recorded brain-cell activity as the rats scurried up and down, pausing at each end to eat, groom and scratch their whiskers.
As the rats ran along the track, the nerve cells fired in a very specific sequence. This is not surprising, because certain cells in this region are known to be triggered when an animal passes through a particular spot in a space.
But researchers were taken aback by what they saw when the rats were resting. Then, the same brain cells replayed the sequence of electrical firing over and over, but in reverse and speeded up.
"It's absolutely original; no one has ever seen this before at all," says Edvard Moser, who studies memory at the Norwegian University of Science and Technology in Trondheim.
This instant replay could help the animals to learn about a recent place and what parts of it are most important, the investigators propose. The re-run could coincide with a burst of the reward chemical dopamine, which is released in the brain when the animal finds food.
By playing the pattern of activity backwards, those brain cells nearest the food fire first and at the same time as the dopamine signal. The idea is that this might etch the position of the food into the rats' brains. "It's saying, 'this is the place I want to be'," says Foster.
If this idea proves true in people, it could have many implications for human learning. It suggests that those idle times, perhaps spent gazing into space, are actually crucial for our brains to replay, and learn from, recent experiences.