Very like squirrels, black-capped chickadees cover their meals, retaining observe of many hundreds of little treasures wedged into cracks or holes in tree bark. When a hen returns to certainly one of their many meals caches, a specific set of nerve cells within the reminiscence middle of their brains provides a quick flash of exercise. When the chickadee goes to a different stash, a unique mixture of neurons lights up.
These neural combos act like bar codes, and figuring out them could give key insights into how episodic reminiscences — accounts of particular previous occasions, like what you probably did in your birthday final 12 months or the place you’ve left your pockets — are encoded and recalled within the mind, researchers report March 29 in Cell.
This sort of reminiscence is difficult to check in animals, says Selmaan Chettih, a neuroscientist at Columbia College. “You possibly can’t simply ask a mouse what reminiscences it shaped right this moment.” However chickadees’ very exact habits offers a golden alternative for researchers. Each time a chickadee makes a cache, it represents a single, well-defined second logged within the hippocampus, a construction within the vertebrate mind important for reminiscence.
To review the birds’ episodic reminiscence, Chettih and his colleagues constructed a particular area made from 128 small, synthetic storage websites. The group inserted small probes into 5 chickadees’ brains to trace {the electrical} exercise of particular person neurons, evaluating that exercise with detailed recordings of the birds’ physique positions and behaviors.
When the birds have been caching and retrieving their seeds, a selected subset of neurons representing 7 p.c or much less of the whole hippocampus would briefly mild up with exercise, Chettih says. Every cache appeared to have its personal distinctive mixture of neurons, or neural bar code, and people bar codes differed even for particular person caches on the identical location.
It’s potential bar codes are a sort of engram, the proposed bodily manifestations of a reminiscence (SN: 1/24/18). Such bar codes are most likely used throughout many species, contemplating how related hippocampus physiology is between animals separated by a whole lot of hundreds of thousands of years of evolution, Chettih says. Nonetheless, extra analysis is required to verify this.
These bar codes appear to work in parallel with one other group of neurons within the hippocampus known as place cells, which encode data on an animal’s location. Place cells have been extensively theorized as the inspiration of episodic reminiscence.
That is partly as a result of our perceptions of reminiscence are enmeshed with location, says Kazumasa Tanaka, a neuroscientist on the Okinawa Institute of Science and Expertise in Japan who was not concerned with the research. “If you recall some particular occasion that occurred previously, that episodic reminiscence can’t be dissociated from the place that occasion occurred, or when that occasion occurred.”
Place cells didn’t change their exercise throughout caching, stunning the researchers. However the findings counsel an added nuance to this understanding of reminiscence, Chettih says, the place the hippocampus creates a separate “index” that binds collectively all of the totally different inputs making up an expertise into a definite reminiscence.
Tanaka notes that there are actually a number of candidates for indexing methods within the hippocampus, and that it’s potential that episodic reminiscence arises from a number of, concurrent coding schemes.
Chettih’s group additionally found a “seed code,” the place neurons encode the presence or absence of a seed in a cache. The potential interconnections between the three totally different neuron exercise patterns — the bar code, the place code and the seed code — intrigues Thomas McHugh, a neuroscientist on the RIKEN Middle for Mind Science in Wakō, Japan, who was not concerned with the analysis.
“Understanding how they work together might be going to inform us much more about how reminiscence works,” McHugh says.
