While adults might be spending the weekend trying to remember where they have hidden a hoard of Easter eggs, the black-capped chickadee has no trouble recalling where its treats are stashed. Now researchers have discovered why: the diminutive birds create a barcode-like memory each time they stash food.
Black-capped chickadees are known for tucking food away during the warmer months – with some estimates suggesting a single bird can hide up to 500,000 food itemsa year. But more remarkable still is their reliability in finding the morsels again.
Now researchers say they have unpicked the mechanism behind the feat. Writing in the journal Cell scientists in the US report how they gave chickadees sporadic access to sunflower seeds within an arena featuring more than 120 locations where food could be stashed.
The behaviour of the birds and the activity at each cache site – be it the storage of food, retrieval of food or checks on a stash – were recorded on video.
The team used an implanted probe in the brain of each bird to record the activity of neurons in its hippocampus – a brain structure crucial for memory formation.
The results show that each time a bird stashed seeds, even if it was in the same location, a different combination of neurons fired in its hippocampus, resulting in a barcode-like pattern of activity.
The same “barcode” was observed when the morsel was retrieved as for when it was cached.
The barcodes were distinct from place cells – neurons in the hippocampus known to be involved in the formation of memories involving specific locations. “The two overlapped randomly so that neurons could be neither, either, or both,” said Dr Selmaan Chettih of Columbia University’s Zuckerman Institute, first author of the study.
Indeed while place cell activity occurred every time the bird visited a cache site, the barcodes only occurred when the bird was actually storing, or retrieving, a seed. Overall, the team suggest a different mechanism is at play when the birds are making memories of specific events, as opposed to when it is making a mental map of an area.
“These results suggest that the barcode represents a specific episodic experience, unique in place and time in the chickadee’s life,” the researchers report.
Chettih added while not yet proven, it was possible the findings also applied to humans and other mammalian brains. “The message is that, when you form a memory of a specific event, your brain may generate a random label which it uses to store information associated with that event, in a way that is analogous to the way a store records information associated with each product to be retrieved when the label is scanned,” he said. “Perhaps another message is that the brains and mental abilities of these tiny, common birds can be quite remarkable.”
