Learning requires active forgetting (removing memories) to allow for new information to come in, experiments with flies by researchers at Tsinghua University and Cold Spring Harbor Laboratory suggest.

The researchers have traced the process to a molecular pathway including a small protein known as Rac. When that mechanism is blocked, flies hold on to newly acquired memories for longer than they otherwise would.

Rac switches on when flies simply forget with the passage of time, they report. It just switches on faster when the insects either get distracted by new information or “confused” by conflicting experiences.

When Rac was blocked, new memories decayed more slowly, extending their life from a few hours to more than a day. When Rac levels were artificially increased in fly neurons, the insects’ new memories were erased more rapidly.