The basolateral amygdala (BLA) is one site of information storage important for forming conditioned fear responses to previously neutral stimuli by pairing them with aversive stimuli. Researchers have begun to question whether the BLA may play a larger, overarching role in memory and behavior. However, the neuronal activity of the BLA during naturalistic behavior. Now, neuroscientists at the Sainsbury Wellcome Centre at University College London (UCL) observed the neuronal activity in this brain region while rats freely engaged with a variety of different ethological stimuli.

Their findings are published in Cell Reports in a paper titled, “Representation of Ethological Events by Basolateral Amygdala Neurons.”

“The accurate interpretation of ethologically relevant stimuli is crucial for survival,” the researchers wrote. “While BLA neuronal responses during fear conditioning are well studied, little is known about how BLA neurons respond during naturalistic events.”

“Traditionally, research has focused on studying the BLA in rats during trained tasks. Instead, we wanted to observe neuronal activity while rats were freely behaving to see if we could find an overarching role for the BLA during natural behavior that might tie together the previous lines of research,” explained Cristina Mazuski, PhD, lead author and research fellow in the lab of John O’Keefe, PhD, professor, cognitive neuroscience, at the Sainsbury Wellcome Centre.

Using Neuropixels, Mazuski and O’Keefe, simultaneously recorded from hundreds of neurons in the rat BLA and correlated single-cell neural activity with complex behavior to identify different classes of cells within the BLA that respond to the ethological stimuli. They identified and described two novel categories of cells in the BLA: event-specific neurons, which responded to only one of the four classes of stimuli, and panresponsive neurons, which responded equally well to most or all of the stimuli.

Strikingly, one-third of the cells showed an active memory response: not only did the neural response last throughout the entire event but it continued after the end of the event for many minutes. The authors speculated that these after-responses might be acting as a memory system telling the rest of the brain that an important event had just occurred and perhaps alerting other brain regions to store information about other aspects of the event and the circumstances surrounding it.

Commenting on these aspects of the results, O’Keefe, the senior author on the paper, said “These findings position the basolateral amygdala at the center of the social/ethological brain and open up a whole research program investigating what other naturally-occurring stimuli the rest of the (normally silent) BLA cells are interested in. They also direct our attention to the memory functions of the amygdala which have not, to date, received sufficient consideration.”

As the researchers were recording from many neurons simultaneously using Neuropixels probes, they were also able to look at the circuit connectivity. By delving into the correlated activity between different single neurons, they could infer the flow of information from more-specific neurons such as those responding to female rats or food to the less-specific panresponsive neurons.

“This initial study opens up a lot of future avenues for research. The next steps are to find out what the responses are sensitive to, how robust they are, and confirm whether they play a role in memory,” concluded Mazuski.

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