The brain stores memories relative to time and place of origin

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Study participants were shown randomly-captured photos from the previous month while in an fMRI machine, and asked to recall the associated memories(Credit: Joe Camoriano)

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Where and when you form new memories affects where they are stored in the brain's hippocampus, which is the memory center in our brain, researchers at Ohio State University found in a new study. They saw evidence that a particular part of the hippocampus stores memories relative to time over durations of at least a month and space over distances of up to 30 km (18.6 mi).

The researchers enlisted nine female volunteers to wear a smartphone around their neck for a month, with an app that automatically took photos throughout the day. At the end of the month, the participants were hooked up to an fMRI scanner and shown 120 of the approximately 5,400 photos produced by their camera. The researchers measured brain activity while the women tried to remember the event depicted in each picture and answer questions about where, when, or both where and when it occurred.

The farther apart the events were in space and time, the more different the activity patterns in the left anterior hippocampus brain were. The researchers believe this supports an emerging view among neuroscientists that the anterior hippocampus is kind of like an indexing system for autobiographical memories.

The measured brain activity indicates that a general impression or "gist" of a memory gets deposited in the left anterior (front) of the hippocampus, "Then there is a process that moves out through the rest of the hippocampus and spreads out through the cortex as we relive the entirety of the memory," says study co-lead Per Sederberg.

Three of the photos taken automatically by the lifeblogging app during the study(Credit: Per Sederberg)

That said, the entirely-female, small sample group stops the researchers from being able to conclusively argue that all people's memories are encoded and decoded in space and time in this way. The researchers hope to repeat the experiment with better, more diverse sampling and also higher-resolution scans that might open the door to analysis of how memories within events are represented relative to each other.

They also believe that this work could reveal new insights into dementia. "People with Alzheimer’s may forget experiences and people because they are not able to effectively target their old memories. They can’t retrieve memories because they can’t get the right general cue to get to that memory," Sederberg says.

There's a very long road ahead before neuroscientists fully solve the mystery of how memories are formed and accessed, especially when the memories are very far apart in time and space (like perhaps a six-month cross-continental road trip from 20 years ago).

"We've got a decade or more of work ahead of us," says Sederberg. "This is just the first step."

A paper describing the research was published in the journal Proceedings of the National Academy of Sciences.

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