Neuroscientists identify role of basolateral amygdala neurons

The basolateral amygdala (BLA) is a brain area that has almost entirely been investigated in relation to fear and emotion. Researchers have just lately begun to wonder if the BLA has a wider, overarching function in memory and behavior. Despite this, little is known about the BLA's neural activity during naturalistic behavior.

Neuroscientists at UCL's Sainsbury Wellcome Centre studied neuronal activity in this brain area while rats were permitted to participate in a range of ethological stimuli to answer these questions. Food, prey, and conspecifics are examples of ethological stimuli that are important to the animal's survival and the transmission of its genes. The researchers show that the BLA has robust reactions to these types of events in a new study published today in Cell Reports.

The rats were naturally intrigued to interact with the naturalistic stimuli in this study because they were significant to them in their daily lives. Male and female rats, food, and a moving toy mouse were among the complex multisensory stimuli used. "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 behaviour that might tie together the previous lines of research," said Cristina Mazuski, Research Fellow in the O'Keefe Lab at the Sainsbury Wellcome Centre and lead author on the paper.

Mazuski and O'Keefe used Neuropixels to record from hundreds of neurons in the rat BLA at the same time and connect single-cell neural activity with complicated behavior to find several classes of cells in the BLA that react to ethological inputs. They discovered and defined two new types of cells in the BLA: event-specific neurons, which reacted to only one of the four stimulus classes, and panresponsive neurons, which responded to most or all of the stimuli equally effectively.

Surprisingly, 1/3 of the cells showed an active memory response, which lasted not only throughout the event but also for many minutes thereafter. The scientists think that these after-responses are operating as a memory system, prompting other brain areas to retain information about various components of the event and the conditions surrounding it.

Prof. O'Keefe, the paper's senior author, said about these aspects of the findings: "These findings position the basolateral amygdala at the centre of the social/ethological brain and open up a whole research programme investigating what other naturally-occuring 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."

The researchers were able to examine the circuit connections while concurrently recording from multiple neurons utilizing Neuropixels probes. They were able to deduce the flow of information from more-specific neurons, such as those responding to female rats or food, to the less-specific panresponsive neurons by looking at the correlated activity of various single 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," Cristina explains.