Where do our memories go when we forget them? Are they erased completely or do they still exist somewhere in our brains?Neuroscientist Dheeraj Roy has found evidence for the latter, which is remarkable because it means it’s possible for the memories to be retrieved.

In a just-published study, the MIT researcher and his team used a technique called optogenetics to restore memories in lab mice with Alzheimer’s disease. They tagged specific neurons associated with an experience (in one case, the mice were put in a chamber and shocked on the foot), then directed bursts of light at those cells, which reactivated forgotten memories. See the Nature study in full and listen to a podcast about the findings. For now, the memory-retrieving technique is thought to be too invasive for humans.

Roy appeared for an Ask Me Anything (AMA) session in Reddit’s Science community, where he talked about memory loss and the future implications of his groundbreaking research. He shared his personal motivator for doing the work he does.

“Watching my own grandmother gradually forget drives me to the laboratory every day with the hope that someday we will be able to help Alzheimer’s disease patients remember,” he wrote.

Some highlights from the AMA:

Nobody knows exactly what happens in your brain when you remember something.

They tested different types of memories, both fear-based spatial/environmental.

Several conclusions from the animal models may be applicable to humans.

Strong memories involving loved ones often last a lot longer than other memories.

So far, the research supports therapies and treatments targeted at early stages of Alzheimer’s disease.

See the full discussion in the original AMA.