From ScienceDaily: "A naturally occurring growth factor significantly boosted retention and prevented forgetting of a fear memory when injected into rats' memory circuitry during time-limited windows when memories become fragile and changeable. ... To our knowledge, this is the first demonstration of potent memory enhancement via a naturally occurring factor that readily passes through the blood-brain barrier - and thus may hold promise for treatment development ... The staying power of a memory depends on the synthesis of new proteins and structural changes in the connections between brain cells. These memory-strengthening changes occur within time-limited windows right after learning, when memories undergo consolidation, and also right after a memory is retrieved, a process called reconsolidation. Hints from other studies led the researchers to suspect that IGF-II plays a role in these processes within the brain's memory center, the hippocampus, where it is relatively highly concentrated. The little-known growth factor is part of the brain's machinery for tissue repair and regeneration; it is important during development and declines with age. ... learning boosted the expression of naturally occurring IGF-II in the hippocampus. So the researchers injected synthetic IGF-II directly into the hippocampus during windows of consolidation or reconsolidation, when memories are malleable. Remarkably, the rats' memory markedly improved - with the effects lasting at least a few weeks. An examination of the animals' brains revealed that IGF-II had strengthened the cellular connections and mechanisms underlying long-term memory - a process called long-term potentiation."