Just because something is in our long-term memory, that doesn't necessarily mean it'll be there forever. This is one reason why we can study for (and pass) a test, only to forget everything the next day when it's no longer relevant. Now, research may have revealed how we might get our lost memories back — through a process that could one day help Alzheimer's patients, too, says io9.
In the study, published last month in the open access journal eLife, researchers started by using serotonin to strengthen new connections between neurons from the marine slug Aplysia californica. Essentially, this sparked the physical changes needed for a long-term memory to take hold. The cells, however, were then treated with a protein inhibitor, which prevented those changes and therefore kept the memories from actually forming. Surprisingly, the UCLA researchers' results showed that although the synapses had been damaged, there were still traces of the memories left.
Next, in a separate experiment looking at actual Aplysia (not just a petri dish of their neurons), the researchers trained the slugs to retract their tails defensively when given a mild shock. After getting the same inhibition treatment as the first study's slug cells, these slugs lost the tail-retraction response. Then, after just a few additional shock re-training sessions — fewer than were required to form the initial long-term memory — the slugs remembered the tail response.
These results suggest that we don't necessarily need all of those initial memory synapses to be in place in order to retrieve our lost memories. Which leads the authors to say that those "stable synapses" may not be quite as essential to long-term memories as we thought they were — and that, way down the line, this could lead to Alzheimer's patients getting their memories back. This concept runs against a lot of our contemporary thinking about how learning and memory are actually kept in the brain.
As you might guess, Aplysia are a long way from humans. Their relatively simple nervous system — made up of only about 20,000 neurons — makes them great for research, but not exactly the easiest species to generalize to others. So, we'll take this as just the first of many exciting steps towards being able to recite our school-play roles from memory once again.