Sleep is known to consolidate memories. But what happens to memories if they are reactivated during sleep?

Björn Rasch at the University of Basel in Switzerland, Jan Born at the University of Lübeck in Germany, and their colleagues asked 24 volunteers to learn the locations of pairs of matching cards in an array while being presented with an odour. Half of the volunteers then slept for 40 minutes. During this period, some of the sleeping and wakeful volunteers were exposed to the odour again, to reactivate their memories. Next, the volunteers learned a second task designed to interfere with their memories from the first. They were then asked to recall the original locations of the cards.

Those exposed to the odour during sleep had a higher memory-recall rate than did those who were not exposed. Conversely, in awake volunteers reactivation of the memories with the odour increased forgetfulness.

Nature Neurosci. doi:10.1038/nn.2744 (2011)