We've all suffered through the last-minute exam cram—that largely futile attempt to memorize as much as possible in the final minutes before a test. No matter how hard we try to remember it all, the information often disappears the minute we read the first question. Whereas forming memories is an active and often exhausting process, losing them seems to happen quite passively as time elapses and new information overloads our busy brains. But a new study published February 19 in the journal Cell shows that forgetting is a biochemically active process not unlike memory formation.

The authors of the study, Yi Zhong and his colleagues from Tsinghua University in Beijing and Cold Spring Harbor Laboratory in Long Island, N.Y., drew their conclusions based on studies of fruit flies. They created Drosophila melanogaster in which they could turn off or turn up a protein called Rac, which plays several roles in intracellular signaling. Then they had the tiny flies perform three memory-forming tests.

In the first, the flies learned to associate one of two odors with a negative consequence (a mild electric shock to a foot). In the second, the flies had to learn a new pair of odors and their consequences—a test called interference learning because it interferes with the memory of the first test. In the final test, called reversal learning, the consequences associated with the first pair of odors were reversed.

The researchers found that inhibiting the production of Rac slowed memory decay over time and suppressed forgetting: the flies performed better for longer on the first test but worse on the interference and reversal tests. Increased Rac activity had the opposite effect—it accelerated memory decay and promoted forgetting. The effects were independent of the formation of memories, because all flies acquired the memory of the first association equally.

Remembering has obvious advantages to our survival. But what about the benefits of forgetting? We might want to eliminate a memory if it's no longer necessary, as in the interference learning test. We might also want to lose a memory that's inconsistent with our current circumstances, as in the reversal learning test. The fly study shows that memory decay and forgetting are active processes at the molecular level—separate from those that make memories and, perhaps, no less important. That's something to remember even before you cram for your next test.

Photo: ISTOCKPHOTO/Stalman