Nature Neurosci. doi:10.1038/nn.2498 (2010)

The making of new memories can interfere with old memories of similar events. However, elevated activity in the brain's hippocampus during new memory formation is associated with the retention of older, related memories, according to work by Brice Kuhl, Anthony Wagner and their team at Stanford University in California.

During the study, volunteers learned to associate pairs of objects while their brain activity was monitored with functional magnetic resonance imaging (fMRI). The volunteers then learned to associate a new selection of pairs, some of which featured an object contained in the original pairs. After they left the fMRI scanner, the volunteers did a memory test. Those who remembered the original pairs had exhibited more activity in their hippocampus when forming the new memories than those who did not.