Memory System Resembles 'Beads On A String': How The Brain Sequences Events Over Time

Memory Is A Sticky Thing, Researchers Say
In studying the brain's hippocampus, researchers at New York University say they understand how the temporal sequencing of memory is unreliable. Photo courtesy of Shutterstock

Though our long-term memory begins by school age, many of us understand the subjective nature of information recall — including anyone who’s ever been involved in either a traffic accident or romantic relationship.

Now, researchers at New York University say they’ve discovered how the brain organizes the sequence of memories, which it deposits into long-term storage as discrete “bits” of memory. In the new issue of Neuron, psychologist Lila Davachi compares these memories to beads on a necklace, offering some insight into the temporal nature of how the brain stores memory.

"Our memories are known to be 'altered' versions of reality, and how time is altered has not been well understood," Davachi, an associate professor, said in a statement. "These findings pinpoint the brain activity that explains why remember some events as having occurred closer together in time and others further apart."

Though our experience in life is continuous, our memories are stored like “beads on a string,” one after another in chronological sequence — with one important caveat. For some unknown reason, the neurological process fails to record an accurate sense of timing between events, spacing some memories closer in time while others are spaced further apart.

"Temporal information is a key organizing principle of memory, so it's important to understand where this organization comes from," Davachi said.

Such understanding may lead to, not necessarily improved treatments, but a greater understanding of neurological conditions such as schizophrenia, whose pathogenic path hampers the brain’s ability to record memory in proper sequential order. In the study, Davachi conducted brain-imaging scans on participants while directing participants to work through some memory exercises. They were shown images of faces and objects along with a scenic photograph. Participants were then asked to imagine those faces and objects in another scene, a technique intended to force the brain to encode new memories in the brain’s hippocampus, a region responsible for memory.

To assess how the brain stored such memory, Davachi later showed participants two stimuli, either the object or face from the study’s first phase. They were then asked to rate the temporal distance between the two memories — the stimulus and the scene — as very close, close, far, and very far.

In the end, analysis of the functional-magnetic resonance imaging tests showed a link between activity in the hippocampus and the temporal distance with which the memories were space. With greater hippocampal activity during a session, memories were recalled as spaced closer together, whereas the inverse was true, too.

"Clearly, the hippocampus is vital in determining how we recall the temporal distances between the many memories we hold, and similarity in the brain across time results in greater temporal proximity of those memories," Davachi said.

The study was funded by the National Institute of Mental Health.

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