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Scientists are studying how the brain forms memories. Sweenshots & Shaymone/Stocksy United
  • Our brains experience the world continuously, but memories are formed in pieces called events.
  • Scientists have discovered specific brain cells that help identify new events and aid in future recall.
  • These findings could open novel avenues of research into memory disorder and disease.

You suddenly find yourself in a new environment. The neurons in your hippocampus start firing faster.

We know this because there are depth electrodes implanted in your brain. You return to somewhere familiar, and your neuron activity slows back down.

When asked later about what you remember from this experience, what can you tell us?

Well, nothing, because you’re a rodent. Sorry.

Depth electrodes are needlelike wires that can measure activity deep within the brain as opposed to just along the surface.

Memory experiments using depth electrodes are usually performed on animals, often rodents.

That’s what makes a new study published in the journal Nature Neuroscience so unusual. It includes depth electrode recordings from human beings.

In this research, recordings were taken from individual neurons in participants’ brains as they watched film clips and formed new memories. The results help scientists better understand not only how memories are formed but also how they’re later recalled.

Jennifer Bramen, PhD, a senior research scientist at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, California, told Healthline that this type of research is rare with human participants.

“This is a well-done study using the best possible technique to answer this question, and it is also a special study because these participants are both rare and in demand,” Bramen said.

So the study is unique, but what exactly did they do? And what does it tell us?

One thing should be made clear: Participants did not have depth electrodes implanted in their brains for the sake of this study.

Depth electrodes are sometimes used as an aid in the treatment of people with drug-resistant epilepsy.

The people who participated in the study already had electrodes for this purpose implanted in their medial temporal lobes. This area of the brain includes the hippocampus and amygdala, which are believed to be involved in memory formation.

In the study, the electrodes recorded activity from individual neurons as participants watched a variety of short film clips. These clips included different types of “boundaries” or narrative jumps.

For example, a clip might depict a couple having coffee at a diner. While the clip continues uninterrupted, there’s no boundary.

Say the film cuts ahead, and now a third person is also seated with the couple. This is a soft boundary. There’s been a break in the action, but we’re obviously still watching part of the same story.

Now take that same couple having coffee, but this time the film cuts to a cheering crowd at a sporting event. This is a hard boundary. The couple and the crowd are two distinct episodes, or “events.”

Researchers found that some neurons respond whenever a boundary — soft or hard — was observed. They called these “boundary cells.”

Other neurons only responded to hard boundaries. Researchers called these “event cells.”

This is important because we can remember individual events that have happened in our lives, but our consciousness is continuous.

This study sheds some light on the physical mechanisms that allow our brains to differentiate one memory from the next, even as they’re forming.

The researchers suggested that when something unpredictable happens, your brain takes note and treats it as a new event.

Later, when you try to remember an event, the boundaries can serve as reference points for your brain based on the particular pattern of neurons that reacted when the memory formed.

And the closer to a boundary something happens, the study suggests, the better the recall.

Experts say these new findings have the potential to guide future research into memory disorder and disease.

Scientists could examine event and boundary cells when memory dysfunctions are present.

“If [the cells are] impaired, then these cells may become potential drug targets. If they are intact, then these cells may tell us ways we can help patients with memory disorders better encode new memories,” Bramen said.

James Giordano, PhD, a professor of neurology at Georgetown University Medical Center in Washington, D.C., told Healthline that a wide array of conditions might benefit from targeting these specific cells.

It could be possible to reduce symptoms of “memory impairment caused by physical and/or psycho-social trauma, as well as particular neurological disorders, including memory-related effects of stroke, and the dementia occurring in various neurodegenerative diseases,” Giordano said.

With time, it may be possible not only to treat these symptoms but to prevent them.