Chickadees can remember where they hide food thanks to unique barcodes.
In a recent study, researchers analyzed these black-capped, white-cheeked curious birds, revealing insights into how episodic memories are encoded in the brain.
Chirp, chirp, tweet
When a bird caches food it needs to remember where that is, for later. In this study, chickadees became guests in an arena with 128 small storage sites specially created for them by scientists. Using small probes connected to five chickadees, the research team followed neural recordings in their brain.
They found that chickadees activate a unique neural pattern comparable to barcodes whenever they store food in a specific location. When they return for the food, their brains light back up with the direct pattern.
Memory geniuses
The team found that each memory is tagged with a unique pattern of activity in the hippocampus, the part of the brain that stores memories. They called the patterns ‘barcodes’ because they are specific; for example, barcodes of two different caches are uncorrelated even if those two caches are right next to each other.
Each cache is a very well-defined, and easily observable moment in time during which a new memory is formed. “By focusing on these special moments in time, we were able to identify patterns of memory-related activity that had not been noticed before,” said Dmitriy Aronov, an assistant professor of Neuroscience at Columbia University’s Zuckerman Institute and co-author of the study, in a statement.
Each barcode includes 7% of the cells in the hippocampus. Why is this important? When a bird makes a cache, 7% of neurons respond. This led the team to conclude that every time a bird returns to one of many food caches, a different combination of neurons lights up.
“These are very striking patterns of activity, but they’re very brief only about a second long on average. If you didn’t know exactly when and why they happened, it would be very easy to miss them,” explained Selmaan Chettih, co-author of the study.
Since chickadees do not migrate during the winter, this is a question of life. Their survival depends on where they hide the food during the warmer season. They can make up to 5,000 stashes per day.
The question remaining is if and how their brains use these barcodes to drive behavior. According to Aronov, it isn’t clear if chickadees activate the barcodes and use those memories of food-caching events when they decide on where to go next.
Picking up answers
The study reveals a lack of evidence that barcodes are unique to chickadees. “Rather, some features of the food-caching behavior might have simply made these patterns detectable in the neural data. These behavioral features include vast numbers of memory storage and recall events that occur at well-defined locations and moments in time,” the team notes.
The team’s findings were published in the journal Cell.
Study Abstract
The hippocampus is critical for episodic memory. Although hippocampal activity represents place and other behaviorally relevant variables, it is unclear how it encodes numerous memories of specific events in life. To study episodic coding, we leveraged the specialized behavior of chickadees—food-caching birds that form memories at well-defined moments in time whenever they cache food for subsequent retrieval. Our recordings during caching revealed very sparse, transient barcode-like patterns of firing across hippocampal neurons. Each “barcode” uniquely represented a caching event and transiently reactivated during the retrieval of that specific cache. Barcodes co-occurred with the conventional activity of place cells but were uncorrelated even for nearby cache locations that had similar place codes. We propose that animals recall episodic memories by reactivating hippocampal barcodes. Similarly to computer hash codes, these patterns assign unique identifiers to different events and could be a mechanism for rapid formation and storage of many non-interfering memories.
