Neural pathways, stained neon green above, carry smell signals through the brain from the basal amygdala to the auditory cortex. Credit Shea Lab/Cold Spring Harbor Laboratory

Imagine you’re at a dinner party but can’t smell the food cooking or hear the bell. Sounds like a dream, right? What if it wasn’t?

“When we experience the world and interact with people, we use all our senses,” Cold Spring Harbor Laboratory Professor Stephen Shea says. “That’s true for animals and humans.” However, that’s not always the case in developmental disorders like autism. These conditions can affect how the brain processes incoming information, making it difficult to interpret the social cues that drive conversations, dates, and other interpersonal activities.

How such signals mix and influence each other in the brain isn’t well understood. Shea and graduate student Alexandra Nowlan traced how smell and hearing interact in mouse brains during a maternal behaviour called pup retrieval to shed light on the subject. This activity isn’t limited to mothers. Surrogates, such as stepmoms and babysitters, can also learn it.

“Pup retrieval is one of the most important things for mothers or caregivers. It requires the ability to smell and hear the pup. These things may merge somewhere in the brain if they are both important. We found a projection from a location called the basal amygdala (BA),” explains Shea.

In mice and humans, the BA is involved in learning and processing social and emotional signals. During pup retrieval, the team found that BA neurons carry smell signals to the brain’s auditory cortex (AC) hearing centre. They merge with incoming sound signals and influence the animal’s response to future sounds—like pups’ cries. Amazingly, when Shea’s team blocked maternal mice from accessing smell signals, their pup retrieval response almost completely broke down.

“We think what’s reaching the AC is being filtered through social-emotional signals from BA neurons,” Shea explains. “That processing can be impaired in autism and neurodegenerative conditions. Many brain parts participate in this behaviour and are very richly controlled.”

Shea’s lab is now exploring how these brain regions connect and interact. Their work may lead to a better understanding of how autism can affect a person’s ability to interpret social cues. But that’s just the beginning.

“The idea that we found a neural circuit that may allow emotional processes to interact with perception directly is fascinating to me,” Shea says. He’s not alone there. His research might yet provide answers to one of humanity’s oldest questions. How do our senses inform the ways we connect and experience the world?