Researchers who analyzed brain activity in sleeping volunteers who had learned to navigate through a computer-generated virtual town have discovered evidence that spatial memories are consolidated during deep sleep.
Also, the researchers say that they have shown for the first time that the activity level in the brain's learning center, the hippocampus, correlates with the improvement in memory performance when the subjects are tested the next day.
According to Philippe Peigneux and his colleagues, "A growing body of experimental evidence shows the influence of sleep on the consolidation of recent memory traces. The underlying hypothesis posits that the information that is acquired during wakefulness is actively altered, restructured, and strengthened during sleep."
However, they said, exploring this consolidation process was difficult because of the complexities of both sleep and memory. For example, sleep consists of two major stages -- rapid eye movement (REM) sleep and non rapid eye movement (NREM) sleep. Evidence from animal studies of learning and sleep indicated that spatial memories seem to be replayed in the hippocampus during the deep "slow wave sleep" (SWS) during the NREM sleep stage.
Peigneux and his colleagues explored the memory consolidation process by asking volunteers to learn the layout of a virtual town that the researchers adapted from a popular computer game. They then tested the subjects on their knowledge of the town by challenging them to quickly find routes through the town to specific locations.
The researchers divided the subjects into three experimental groups: