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We’re learning night … and day

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28.03.2006

We already knew that sleeping helped to reinforce what we’ve learned. But today, a study at the ULg demonstrates for the first time that the brain doesn’t wait until night to structure information. Day and night, the brain doesn’t stop (re)working what we learn.

Positron Emission Tomography (PET-scan) studies carried out recently at the ULg Cyclotron Research Centre have revealed the reactivation of cerebral activity associated with learning new information in humans while they sleep. (1,2) This supports the hypothesis of the role of sleep in memorizing.

Taking advantage of the new opportunities offered by 3 Tesla’s functional Magnetic Resonance Imaging (fMRI)(*), Philippe Peigneux and his colleagues at the University of Liege published findings this week in the international journal PLoS Biology (3). Their study revealed for the first time a phenomenon that occurs during active waking that is similar to reactivation of the cerebral activity linked to learning.

To arrive at this result, every half hour, they recorded (or scanned) the cerebral activity of volunteers while they performed a ten-minute auditive attention task, during two sessions spaced out over a few weeks. At each of these sessions, during the half hour between the first two scans of the attention task, the volunteer was given something new to learn. A third scan was then performed after a half-hour rest. During one of the two sessions, the learning consisted in the volunteer memorizing a route in a virtual city he or she was exploring on a computer. This spatial navigation task is known to be dependent on the hippocampus, a cerebral structure that plays a vital role in learning, and damage to which results in inability to memorize new facts (known as anterograde amnesia). The other session was devoted to acquisition by repetition (or procedural learning) of new visuomotor sequences. For this task, it is not necessary that the subject be aware of what he or she is learning, and its success depends mainly on the integrity of the striatum and the related motor regions.

Analysis of the results demonstrated that, compared with the first scan, the cerebral activity evoked by the auditive attention task during the second and third scans was systematically modified by the kind of learning experience that took place between the first and second scans, and this happened in the cerebral regions associated with this learning. Moreover, this post-learning cerebral activity evolves differently over time depending on the type of learning, and is related to the performance level achieved by the subjects when they are tested on the quality of their memory at the end of the session. These elements indicate active processing of the newly formed mnestic traces during the post-learning waking, which could occur at the same time as other cognitive tasks.

More generally, this study from the ULg Cyclotron Research Centre demonstrates for the first time that the human brain does not simply put newly acquired information in standby until there is a period of calm or sleep to strengthen them, but rather continues to process them dynamically as soon as the learning episode has ended, even if the brain has to face an uninterrupted series of completely different cognitive activities.

Philippe Peigneux, PhD | Source: alphagalileo
Further information: biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040100
www.ulg.ac.be

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