Psychologists have known for some time that during sleep the mind works like a secretary, toiling over the mass of information we take in every day, collating, organizing and storing it for future use. A study published last week in PLoS Biology shows that this kind of administrative maneuvering takes place during your waking hours as well, even as new information accumulates.
"If you acquire some information during your wakefulness, and then it is in part consolidated during sleep, then the question is, 'Where and how is the information stored during wakefulness, before sleeping?'" said Philippe Peigneux of the University of Liège in Belgium, head author of the study. "If you have to learn something now, at noon, you will also have to learn a lot of other things after that, before sleeping."
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Peigneux and his team used fMRI to map brain activity at three stages of information processing. First, to get a baseline reading, they scanned their subjects as the latter carried out a basic attention task, listening to a series of repetitive tones and counting them. Following the initial scan, the study's participants spent half an hour learning one of two sequence activities: either a spatial exercise of navigating a passageway through a computer maze or a set of finger movements to test motor memory. Immediately after the learning tasks, volunteers were scanned while they performed the original counting task. After a half-hour wait, they were then scanned again, while performing the counting task again.
Studying the final two scans, the scientists found that, even though subjects were actively performing the counting task, the parts of their brains that had worked to memorize the learning tasks were still whirring away, synthesizing that material even as newer information entered the system.
"If I take the example of the spatial navigation task, it is known to activate the hippocampal area—so the hippocampus and related areas of the brain," said Peigneux. "If we compare activity just after learning, with the activity just before learning in the same counting task, there was higher activity in the hippocampus after the learning task."
Peigneux also observed that the brain absorbed different types of learning at varying speeds. As subjects performed the navigation task, activity in the hippocampal area accelerated quickly and then stabilized during the waiting period with no marked change between the second two scans. After a subject performed the motor sequence, researchers found that the activity in the basal ganglia and premotor cortex actually decreased and then increased some time later.
"There is a different temporal dynamic [involved] in the development of different types of memories," Peigneux said. "The spatial navigation task is a very different type of memory than the motor sequence learning habits that we learn."