For a long-term memory to form in our noggins, a complex chain of cellular events needs to kick into action. It starts with chemical cues set off by a behavior or experience that make their way to specific nerve cells in the brain. Upon arrival to those cells, the chemical signals are ferried from the outer waiting area of the cell to the nucleus—a cell’s command center where the genetic blueprints are kept. In the nucleus, the molecular messenger can persuade the cell to switch on or off genes—which can strengthen nerve connections and, ultimately, lock down a memory for long-term recall.

While those general steps are clear, the details are still a bit fuzzy. For instance, researchers don’t know how exactly the molecular signals get shuttled to the command center, which generally has tight security. But a new study may finally have that answer.

In the tiny minds of fruit flies, a protein called importin-7 acts to shuttle the memory-triggering signal into the nucleus with its top-level clearance to the restricted area, researchers report in the Proceedings of the National Academy of Sciences. Because this step of long-term memory formation seems the same in everything from flies to humans, and humans have their own version of importin-7, the finding could help fill in the details of how our minds form memories, the authors suggest.

The researchers, led by neuroscientist Yi Zhong of Tsinghua University in Beijing, had an inkling of importin-7’s role after previous research flagged the protein as being important for long-term memory formation.

To test out the idea, the researchers toyed with long-term memories in flies using Pavlovian conditioning. That training involved putting 100 flies in a tight chamber wired with a copper grid that could deliver little electrical zaps. Then, the researchers blew in one of two smells. One of the smelly breezes was always followed by an electrical zap, while the other was not.

To test the flies’ memory of the shocking experience, the researchers would then move the insects to a T-shaped maze, where each arm of the maze smelled like one of the two chemicals. The researchers tallied how many of the flies remembered to avoid the arm with the smell that preceded a jolt in their training.

With genetic tweaking, the researchers dialed up and down the amount of importin-7 in the flies and then put them through the memory training and test. They found that cranking up levels of the shuttle protein strengthened the long-term memories of the flies, while turning it off weakened their memory.

Using fluorescent tags to track the memory signal, called mitogen-activated protein kinase (MAPK), researchers also found that importin-7 was critical for giving MAPK an all-access pass to the nucleus.

“The current work confirms that [importin-7] is indeed critical at the behavioral level in mediating [long-term memory] consolidation,” the authors concluded.

Proceedings of the National Academy of Sciences, 2015. DOI: 10.1073/pnas.1520401113 (About DOIs).