Very similar to squirrels, black-capped chickadees disguise their meals, retaining monitor of many hundreds of little treasures wedged into cracks or holes in tree bark. When a hen returns to one among 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 might 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 review in animals, says Selmaan Chettih, a neuroscientist at Columbia College. “You possibly can’t simply ask a mouse what reminiscences it fashioned in the present day.” However chickadees’ very exact conduct gives 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 check the birds’ episodic reminiscence, Chettih and his colleagues constructed a particular area fabricated 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 had been caching and retrieving their seeds, a selected subset of neurons representing 7 p.c or much less of the complete 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 attainable bar codes are a sort of engram, the proposed bodily manifestations of a reminiscence (SN: 1/24/18). Such bar codes are in all probability used throughout many species, contemplating how comparable hippocampus physiology is between animals separated by a whole bunch of tens of millions 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 referred to as place cells, which encode info on an animal’s location. Place cells have been broadly 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 Know-how in Japan who was not concerned with the research. “While you recall some particular occasion that occurred prior to now, 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, shocking the researchers. However the findings recommend an added nuance to this understanding of reminiscence, Chettih says, the place the hippocampus creates a separate “index” that binds collectively all of the completely 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 attainable 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 completely 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.
