Medical News
Mind
27 June 2019
Even at rest our brains are working hardWestend61/Getty
By Jessica HamzelouOur brains never really switch off. When we rest, neurons fire to replay recent experiences – and this seems to improve our ability to make decisions.
This replay happens in a region called the hippocampus, which is known to be important for memory. Past research has shown that, when rats navigate a maze, the activity of neurons in the hippocampus follows a pattern. This pattern is then replayed – speeded up by a factor of 20 – when the rats sleep or rest.
Rats also seem to use this replay to make decisions. When making its way through a maze, a rat will pause at a junction, replay memories, and then continue down one arm, says Nicolas Schuck at the Max Planck Institute for Human Development in Berlin.
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Human minds
But what about humans? To find out if our minds replay memories to aid decision making, Schuck and Yael Niv at Princeton University in New Jersey looked at the brain activity of 33 volunteers while they performed a task in an fMRI brain scanner.
In the task, the volunteers were shown a series of images, each of which contained a semi-transparent human face laid over a picture of a house, so that both were visible. They were asked to start focusing on faces in consecutive images, judging each as young or old. After a series of faces in the same age category the volunteers were suddenly presented with a face in the alternative age category. This was a signal for them to switch their attention to the houses in the images, and judge them as young or old. Again, they would see a series of houses in the same age category and then encounter a house in the opposite age category, which was a signal to switch focus back to the faces, and so on.
By looking at the activity in the hippocampus, Schuck and Niv could see that the volunteers’ brains seemed to play out patterns of activity during the house/face judging task, and then replay them later, during a rest break.
Neural activity
The pair found that the more replay there was during the rest break, the better a brain region called the orbitofrontal cortex could create a distinct pattern of neural activity related to the specific experience of carrying out the task. This suggests that more replay helps build a better representation of the world around us.
People who had better representations also went on to perform better in the task, measured in terms of the accuracy with which they judged the age of the houses or faces. This suggests they seem to be better at decision-making, says Niv.
“We know it’s best to learn a little bit at a time and let it sink in,” she says. “We now have a neural measurement of what that sinking means… let the hippocampus play it back to the orbitofrontal cortex and other areas of the brain that are listening, and learn from it.”
Journal reference: Science, DOI: 10.1126/science.aaw5181
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