Chickadees have unique neural barcodes for episodic memories, researchers say| Trending Viral hub

Black-capped chickadees (Poecil atricillaus), small North American passerine birds that live in deciduous and mixed forests, have an extraordinary memory that can remember the location of thousands of morsels of food to help them survive the winter. Now, scientists from Zuckerman Institute for Mind-Brain Behavior at Columbia University have discovered how chickadees can remember so many details: they memorize the location of each food item using brain cell activity similar to a barcode.

Chettih et al.  propose that animals remember episodic memories by reactivating barcodes in the hippocampus.  Image credit: Chettih et al., doi: 10.1016/j.cell.2024.02.032.

Chety et al. propose that animals remember episodic memories by reactivating barcodes in the hippocampus. Image credit: Chettih. et al., doi: 10.1016/j.cell.2024.02.032.

“We found that each memory is marked with a unique pattern of activity in the hippocampus, the part of the brain that stores memories,” said Dr. Dmitriy Aronov, lead author of the study.

“We call these patterns ‘barcodes’ because they are extremely specific labels of individual memories; for example, barcodes from two different caches are not correlated even if those two caches are next to each other.”

“There are many findings in humans that are entirely consistent with a barcoding mechanism,” added Dr. Selmaan Chettih, first author of the study.

Scientists have known for decades that the brain’s hippocampus is necessary for episodic memory, but it had been much more difficult to understand exactly how those memories were encoded.

This is partly because in most cases it is difficult to know what an animal might be remembering at any given time.

To address this issue in the new study, Dr. Aronov and his colleagues looked at chickadees.

They realized that chickadees offered a unique opportunity to study episodic memories because birds store food and then must remember to come back for it later.

“Each cache is a well-defined, manifest, and easily observable moment in time during which a new memory is formed,” Dr. Aronov said.

“By focusing on these special moments in time, we were able to identify patterns of memory-related activity that had not been noticed before.”

The researchers had to design scenarios that allowed for detailed, automated monitoring of behavior while the chickadees stored and retrieved food.

They also had to develop technologies for dense, large-scale neural recordings in their brains while the birds moved freely.

Their brain recordings during caching revealed very sparse and transient barcode-like patterns of activation across hippocampal neurons. Each barcode involves only about 7% of the hippocampal cells.

“When a bird creates a cache, about 7% of the neurons respond to that cache. When a bird makes a different cache, a different group of 7% of neurons respond,” Dr. Aronov said.

Those neural barcodes occurred alongside the conventional activity of neurons in the brain that fire in response to particular places, appropriately called place cells.

But interestingly, the episodic memory barcodes for caching locations close to each other bore no resemblance.

“It was widely assumed that when an animal forms a new memory, the cells change location,” Dr. Aronov said.

“For example, placing cells could increase or decrease their activation near a cache location.”

“Although this was the predominant hypothesis, it was not supported by our data.”

“It appears that place cells do not represent information about hiding places and rather remain relatively stable while a chickadee stores and retrieves food in the environment.”

“Instead, episodic memories are represented by an additional pattern of activity, the barcode, that coexists with place cells.”

The authors compare the newly discovered hippocampal barcodes with computer hash codes, which are patterns assigned as unique identifiers to different events.

They suggest that barcode-like patterns could be a mechanism for the rapid formation and storage of many non-interfering memories.

“Perhaps the most important question is whether and how the brain uses barcodes to drive behavior,” Dr. Aronov said.

“It’s not clear whether chickadees activate barcodes and use those memories of food-storing events when making decisions about where to go next, for example.”

“These are questions we plan to address in future studies through more complex environments in the laboratory in which we will record brain activity as the birds choose which food caches to visit.”

“That’s what we might expect if they plan to retrieve a cached item before doing so,” Dr. Chettih said.

“We want to identify those moments when a bird is thinking about a location but isn’t there yet, and see if activating a barcode could prompt the bird to go to a cache.”

“We are also eager to know if the barcoding tactic they have discovered in chickadees is widely used among other animals, including humans. “This research can help shed light on a fundamental 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 particular events are fundamental to that. “That’s what we’re trying to understand.”

TO paper about the findings was published in the journal Cell.

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Selmaan N. Chettih et al. Barcoding episodic memories in the hippocampus of a food-caching bird. Cell, published online March 29, 2024; doi:10.1016/j.cell.2024.02.032

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