Science 325, 1258–1261 (2009)

When adult rats are trained to associate a sound with an electric shock, they will often fear that sound for a lifetime. Young rats, however, can erase the fear memory when it is no longer relevant.

Andreas Lüthi, Cyril Herry and their colleagues at the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland, found that the reason for the shift may be the development of the perineuronal net, an extracellular protein lattice that surrounds a subset of neurons as rats mature. When the authors used an enzyme to dissolve the perineuronal net in the amygdala, a crucial brain region for forming fear memories, they found that adult rats could wipe away the memory of the shock as if they were young.