There is comfort in trusting the immutability of memory—that a favorite birthday or a baby’s first laugh are unalterably imprinted in our brains. In truth, says neurobiologist Kerrie Thomas of the University of Cardiff in Wales, the mere act of recalling an event opens it up to manipulation and reinterpretation.
Thomas is experimenting on rats, injecting the animals with bits of genetic material that block the proteins needed to form new memories and to store established ones after they are recalled. She then exposed the rats to events designed to teach them to fear a previously safe place (where they would now receive a mild electric shock). Interfering with a protein called BDNF prevented the rats from remembering which locations produced the unpleasant event. Inhibiting a second protein called Zif268 had a stranger, more subtle result: Rats were initially able to learn and remember the places to avoid but then suffered amnesia. Without Zif268, the fear memory could not be saved again.
The implication is that putting a recalled memory back into storage involves a different chemical pathway than does forging the original memory. Dual memory pathways may help the brain increase its total computational power while incorporating new information with existing data in meaningful ways. The split also means it might be possible to interfere with specific recalled memories without damaging all the others. Drugs that block Zif268 or related proteins could potentially suppress post-traumatic stress disorder, phobias, and drug addiction, in which persistent memories lead to damaging behavior, Thomas says.