We may not be able to gun it to 88 miles per hour and suddenly arrive in a different point in time, leaving fiery ghost trails burning where we once were. But we can walk around in our own thoughts and past experiences, reviving old sounds and smells as if they were mint. Compared to visions of going back to the future, mental time travel may be the next best thing.

Understanding how the brain makes sense of the past is important for understanding how it sorts the fluid present. With diseases like Alzheimer’s and other dementias still sitting as daunting question marks with respect to both prevention and treatment, brain science is increasingly turning to backdoor methods of discovery. If researchers can’t look directly at the brain as it degenerates, maybe they can look at the parts that make up the total, and, importantly, salvage what’s left.

“If we want to help someone with Alzheimer’s disease or dementia, we want to know how the brain targets and retrieves memories of past experience,” said Sean Polyn, assistant professor of psychology at Vanderbilt University.

With the help of two graduate students, Polyn recently took to the lab to explore those curiosities more in-depth. They pooled 20 participants between 18 and 35 years old. Each was asked to remember a list of 24 words — common objects like horse, boat, and window — and told to repeat the string of words in order. All this was completed as subjects lay inside an fMRI scanner, which the researchers used to track neural activity.

The team was looking at one region in particular: the medial temporal lobe. Memory research is decidedly fickle, but the evidence that does exist suggests it’s here that long-term memories play the largest role. Polyn and his colleagues wanted to learn how it plays that role.

To do that, they created a model that simplifies the neural architecture of memory and spits out the odds that a person will retrieve the words in-order based on past performance. From that model the team can decipher which memories are “high fidelity,” meaning they are richer and packed with context, and which are isolated recollections. The more experiences that appear as high fidelity indicate the person is mentally time travelling, and therefore faces a greater chance of recalling the words on either side of the target word.

Polyn likens the process to Google. Google can’t find what you’re looking for unless the search terms pertain to the subject. That’s why you can struggle all day to recall the title to a song with which you’re intimately familiar, then suddenly hear a word that makes an association somewhere in your brain and you retrieve the memory. “It’s like you’re able to construct, neurally, these better search terms that specify, ‘I want memories from this particular moment, this past moment in time,’” he said. High-fidelity memories — the ones that let you mentally time travel — are the equivalent of telling Google you want hotels in Paris when that’s exactly what you’re after. But if the mental context isn’t there, you might as well be looking up lawnmowers in Memphis.

Alzheimer’s patients stand a lot to gain from research of this variety, Polyn says. Aside from recommendations to eat healthy, exercise, and maintain an active social life, doctors can’t offer any advice to stave off neurodegeneration. “If you’re going to have some hope of developing a treatment for someone who’s having trouble retrieving memories,” Polyn said, “you want to know what brain regions are most critically involved in that process, so you know where to look for a problem.”

The ultimate goal, he says, is to have as much of that information as possible when the moment is ripe for science to intervene. If a patient transitions from recalling high-fidelity memories to isolated recollections, that may indicate gradual memory loss or early onset Alzheimer’s. With the right tools, that could mean the difference between stopping the disease in its tracks and letting the patient get utterly engulfed.

Source: Kragel J, Morton N, Polyn S. Memory And Mental Time Travel: New Understanding Offers Clues For Solving Alzheimer's. Journal of Neuroscience. 2015.