April 24, 2024

Chickadees have unique neural “barcodes” for food storage memories

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Chickadee. Credit: Dmitriy Aronov

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Chickadee. Credit: Dmitriy Aronov

Black-billed tits have extraordinary memories that can recall the location of thousands of pieces of food to help them survive the winter. Now, scientists at Columbia’s Zuckerman Institute have discovered how chickadees can remember so many details: They memorize each food location using bar code-like brain cell activity. These new discoveries could shed light on how the brain creates memories for the events that make up our lives.

“We see the world through our memories of objects, places and people,” said Dmitriy Aronov, Ph.D., principal investigator at Columbia’s Zuckerman Institute and assistant professor of neuroscience at Columbia’s Vagelos College of Physicians and Surgeons.

“Memories entirely define the way we see and interact with the world. With this bird, we have a way of understanding memory in an incredibly simplified way, and by understanding its memory, we will understand something about ourselves.”

This barcode-like memory formatting, first revealed in the magazine Cellit may be a common tactic in animal brains, including those of humans.

“There are many findings in humans that are completely consistent with a barcode mechanism,” said postdoctoral researcher Selmaan Chettih, Ph.D., who co-authored the study with Emily Mackevicius, Ph.D.

Chickadees are “memory geniuses,” said Dr. Aronov, corresponding author of the study. They are masters of episodic memory – the brain’s ability to remember specific moments, like storing some food under the bark of a tree or in a hole. This can be a matter of life and death for them, as, unlike most birds that live in cold places, tits do not migrate during the winter. This means their survival depends on remembering where they hid their food during the warmer months, with some making up to 5,000 such hiding spots a day.

Chickadees storing seeds in the testing arena. Credit: Cell/Chettih et al.

Scientists have long known that these birds rely on the hippocampus – a brain structure critical for memory in all vertebrates, including humans – to store memories of their hiding places. However, no one has identified the specific neural activity in the hippocampus that encodes episodic memories such as food storage events.

“The question we’re trying to answer is, ‘What physically is a memory?'” Chettih said.

Chickadees can help scientists unravel this mystery. To explore chickadees’ prodigious memories, Dr. Aronov and his team built indoor arenas inspired by the birds’ natural habitats.

“Scientists have been amazed at these birds’ memories for decades, but what has been a mystery is what goes on in their brains to support those memories,” said Dr. “We now have neural recording and behavior tracking tools at hand. our willingness to advance our knowledge of how these birds are able to perform these feats of memory.”

In typical experiments, a black-capped tit instinctively hides sunflower seeds in holes in arenas while researchers monitor activity in the hippocampus. Meanwhile, six cameras also record the birds as they fly, with an artificial intelligence system automatically tracking them as they store and retrieve seeds.

Chick seed cache with 3D postural tracking. Credit: Cell/Chettih et al.

Scientists unexpectedly discovered that each time a chickadee saved a seed, hippocampal neurons fired in a unique pattern. These fleeting patterns were reactivated when the birds retrieved that specific cache of food.

“These are very striking patterns of activity, but they are very brief – only about a second long on average,” said Dr. Chettih. “If you didn’t know exactly when and why they happened, it would be very easy to miss.”

As the researchers reflected on their data, the idea of ​​neural barcodes as unique labels for different events began to make sense, they said.

These barcode patterns exist independently of the activity of hippocampal neurons, called place cells, which encode memories of locations. Each barcode remains distinct, even when dealing with caches hidden in the same location but at different times, or neighboring caches made in quick succession.

“Many studies of the hippocampus have focused on place cells, and the Nobel Prize was awarded for their discovery in 2014,” said Dr.

“So the assumption in the field was that episodic memory must have something to do with changes in place cells. We found that place cells don’t actually change when birds form new memories. Instead, during food storage, there are patterns additional activity beyond that seen with local cells.”

In the future, researchers want to see if chickadees activate barcodes when searching for caches in remote locations.

“This is what we would expect if they planned to retrieve a cached item before actually doing so,” Chettih said. “We want to identify those moments when a bird is thinking about a location but hasn’t gotten there yet, and see if activating a barcode can prompt a bird to head to a hiding spot.”

The researchers are also eager to learn whether the barcoding tactic they discovered in chickadees is widely used among other animals, including humans. This research could help illuminate a central part of the human experience.

“If you think about how people define themselves, who they think they are, their sense of identity, then episodic memories of specific events are fundamental to that,” Dr. Chettih said. “That’s what we’re trying to understand.”

More information:
Barcoding episodic memories in the hippocampus of a bird that stores food, Cell (2024). DOI: 10.1016/j.cell.2024.02.032. www.cell.com/cell/fulltext/S0092-8674(24)00235-6

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