On a cool evening in early fall, the Memorial Union Terrace is alive with voices. The sound is ambient, swelling, punctuated with laughter. It feels good to walk through this happy hum. Taking a seat, you feel ridiculously lighthearted, your worries on hold for an hour or two, as you turn to the friend who biked here to meet you.

“So, what’s up with you?”

Humans, like songbirds, are pro-social animals. We love to gather in groups and chirp about whatever comes to mind, and there’s a biological reason that’s so: The activity triggers the natural reward system of the brain. It’s a neural process that’s been conserved for over 300 million years, since the time when birds and mammals shared a common ancestor. And while mammal brains and bird brains may look completely different from one another today, many neuroanatomical connections and neurochemicals remain the same, according to biologist Lauren Riters. Riters studies the neural regulation of vocal communication in songbirds and is particularly interested in how the brain’s natural motivation and reward systems respond to social stimuli. Her work with European starlings—a species that gathers in huge groups in the fall and holds noisy confabs that sound, even to the casual listener, like animated conversations—reveals exciting new insights into the motivation to flock and the deep rewards of singing together. The research may also lead to treatments to restore positive social interactions in humans, where they’ve gone awry.

“My lab members and I are really interested in the role that reward plays in shaping communication,” Riters says. “It became so clear to me, during the COVID-19 pandemic, how painful it is to be separated from social groups and how rewarding social interactions can be.”

For the last 20 years, the Riters lab has received funding from the National Institute of Mental Health to study the motivation to communicate in songbirds. “By studying conserved neural pathways that regulate the motivation to communicate, we provide new information on how this can go amiss,” Riters says.

Every summer, Lauren Riters and her graduate students refurbish the starlings' aviaries and begin observing them. Photo: Paulius Musteikis

European starlings may be considered non-native pests by many (including Wisconsin farmers), but they exhibit remarkable vocal communication skills in different social contexts. The birds live in a breezy outdoor aviary. Riters and her students observe their behavior year-round in both the breeding season (when the males are stridently vocal and territorial) and—with particular interest—in fall, when the birds join together in flocks and the singing takes a different form.

“We became fascinated by the song in flocks,” Riters says. “It seemed like they were singing for no reason. There aren’t too many things that animals do for no good reason. The exception to that is playful behavior.”

With no pressure to defend nests or attract a mate, could the starlings be singing their “flock song” simply because it feels good?

Using behaviorist Gordon Burghardt’s criteria for play, Riters and her team set out to discover whether fall singing—which, by the way, occurs only in flocks, unlike spring song—was a playful behavior.

“Courtship song in spring, sung only by males, is more rigid and precisely sequenced,” Riters notes. “The song that males and females are singing together in a flock in the fall is more like riffing. We say it’s a little like free-form jazz—some notes are out of order. They are a little sloppy.”

That matches with the definition of play behavior as low-stakes practice, something that occurs in non-stressful situations, hones skills or comes in handy later in life, but for the moment, is just enjoyable. But the team needed more.

Starlings perched inside their outdoor aviary Photo: Paulius Musteikis

“You can’t just ask a bird if it’s having fun,” Riters says, “and we were pretty sure that opioids were involved in what seemed like a pleasurable activity. So, we borrowed methods from psychology to ‘ask’ a bird how it’s feeling and to explore a role for opioids.”

The team administered tiny doses of fentanyl—an opioid that binds to what’s called the mu receptor in the brain and has a similar effect as the naturally occurring opioids that light up bird and human brains when they are in a “reward state”—to the starlings. The birds responded by ramping up their singing. The team then ran a “conditioned place preference” (CPP) test to ask birds if it “feels good” to sing. They trained the birds to associate a color­ful location with singing, and later, when given a choice between two locations, birds showed a strong preference for the place that they’d learned to associate with their own singing behavior. This suggests that a positive association had developed between singing and the place. The team then found that temporarily “turning off” the opioid receptors disrupted the place preference (the findings were shared in Scientific Reports in 2020 and summarized in a UW news article shortly thereafter).

The experiments offered strong evidence that flock song involves intrinsic reward for birds. Whether birds’ opioids are released because of the singing or because of the flocking is still under investigation, Riters says.

“Is there something about being in the flock that is rewarding?” she muses. “I think that’s true. It feels bad to be alone. As a human being, it felt bad to be alone during the pandemic. We wanted to be together so much that we had to introduce laws and rules to keep us from interacting. We are a social species, and we hate to be separated. And starlings are incredibly social too, especially in fall.”

Alyse Maksimoski, a PhD student in the Riters lab, studies flocking behavior. Right now, she’s trying to determine whether starlings experience a “joy of reunion” after a brief separation from the flock.

“I’m pursuing questions that are very much relevant to what people have gone through during the COVID-19 pandemic,” she notes.

European starlings often form undulating flocks — called murmurations — in late fall, after gathering in social groups for weeks to sing playfully together. Photo: Rolf Nussbaumer / Alamy

Maksimoski is exploring the possibility that when they flock, birds’ brains, like humans’ brains, light up with dopamine, which motivates behavior and directs it toward reward. Once together, they also sing like crazy.

“The more an individual experiences social cohesion, the more motivated it is to seek out social opportunities in a gregarious setting,” Maksimoski says. “I’m studying what happens when birds have brief social separation. What do they do when they get back into the flock—do they start singing? Do they exhibit a behavior that indicates joy? How does this relate to dopamine signaling?”

Maksimoski compares flocking and singing in a group to humans doing yoga in a class or gathering on the Terrace together. What remains for the team to prove is “directionality”—which comes first, the singing, or the opioids? The dopamine, or the flocking?

An interesting finding, Maksimoski says, is that when birds are central to the flock and singing at high rates, they are more motivated to seek out social opportunities. And some birds, even in flocks, seem to have different spatial needs—they want to be close, but not too close, integrated but not too integrated.

I’m studying what happens when birds have brief social separation. What do they do when they get back into the flock—do they start singing? Do they exhibit a behavior that indicates joy? How does this relate to dopamine signaling?

Alyse Maksimoski

“This is something we weren’t con­sidering,” says Maksimoski. “Most birds are gregarious, it’s true. But what if the degree of social cohesion differs? What if the need for social integration is highly individualized?”

Another PhD student in the Riters lab, Brandon Polzin, studies the role of shared neural mechanisms that underlie social behavior by examining “conserved neural structures” involved in rewarding behaviors across vertebrates.

Identifying common neural structures means researchers may extrapolate their findings more easily to humans. Polzin is also examining how glutamate, another natural neurochemical, integrates with opioid and dopamine pathways as part of what he calls “an interesting mystery.”

“In certain mental health disorders—major depressive disorder and generalized anxiety disorder—we see social commu­nication and social motivation heavily impacted, and affiliative social behavior can lose its reward value in people with these disorders.”

Being able to identify the specific neurochemical systems and the specific regions that are involved in these pro-social interactions, he says, will help scientists understand what systems could be dysregulated and could highlight what might be possible therapeutic targets in the future.

Riters says UW-Madison is a great, supportive environment for this work, with low barriers to collaborating and interacting across disciplines. She and her graduate students study animal behavior and neuroscience, but they meet with psychologists, mental health experts, colleagues in the psychiatry department and others to compare methods and insights. All this enables them to design better experiments, draw more nuanced conclusions, and move ever closer to an understanding of the brain’s complex systems of motivation and reward.

“I think what’s most exciting to me is that we can study this naturally occurring behavior in songbirds and maybe provide something that could help with mental illnesses in humans,” Riters says.

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