California's "singing" fish have a surprising relationship to mammals, study finds

What did one California singing fish say to the other? We’re not entirely sure either, but if anyone might be able to translate, it would be the researchers at Cornell University. In a new study of the species — better known as midshipman fish because their spots look like little sailor uniforms — scientists found the aquatic crooners are using the same part of their brains as mammals use when talking to one another. 

Whether on the prowl for mates or fending of competitors, male midshipman fish (Porichthys notatus) become quite the chatterboxes. The species are known to grunt, growl and even hum — the latter of which might even sound like a foghorn or a single note played on a French horn, according to Cornell University professor and study senior author Andrew Bass. And when it comes to piping up or figuring out what patterns to sing, it’s the midbrain section of the fish’s brains which plays a central role. Just like in humans. 

Interestingly, it wasn’t the fish that initially drew Bass into the water for research, but the birds. He was inspired by the seminal studies of bird vocalizations in the 1990s, in particular one on the midbrains of finches.

“Honestly, it was my reading of that work when I was a graduate student that got me excited about the possibility,” he told Salon. “I thought, ‘we all know that fish have a similar part of the brain. Maybe something could happen there.’”

So far, midbrain activity has been under-explored when it comes to how it enables different species of animals — humans included — to communicate vocally, whether through fishy hums or human sentences. But the study, published earlier this month in the journal Nature Communications, explores how these midbrain-sparked vocal patterns among the fish could help us understand vocal control and expression among humans and other vertebrates.

“It’s only been in the past few years, where the midbrain has gotten more attention from neuroscientists studying social communication,” Bass said in an earlier statement. “It is a major node connected to your cortex, basal ganglia, amygdala and hypothalamus. In this way it acts as a gateway for these sources of executive functions to reach other brain regions more directly activating muscles that underlie behavioral actions.”

Analyzing the aquatically loquacious may also give us clues about whether midbrain injuries in humans may be linked to a person being mute or uncommunicative, according to Bass. 

“The midbrain is an amazing part of the brain because it points to how essential it is – if you are a vertebrate – to have the ability to produce sound communication signals. Period,” Bass said.

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Bass’ dive into the neuroscience of acoustic communication couldn’t come at a better time. The topic of vocalizations across species — especially as it might reveal the origin of human speech — has been sorely understudied. While this places a burden of work on future research, it also means it is an exciting time for the field. 

In November, scientists at the University of Zurich joined an international team of researchers to produce a landmark study on acoustic communication among 53 different species, including turtles and other amphibians. 

"New research is needed to better understand the usage of these sounds by these animals, together with their social behavior and cognitive functions," lead researcher Gabriel Jorgewich-Cohen pointed out to Salon in November 2022. 

"Studies focused on vocal behavior during the transition from water (fish) to land (tetrapods) can also help to clarify if this behavior appeared 400 [million years before the present], like we suggest, or if this is actually a much older behavior that we may share with some lineages of bony fish."

One of the reasons fish brains can be so helpful in understanding humans’ is that they’re generally just easier for scientists to dig into. If you think of the shape of a typical human brain — a bit like a helmet — our midbrains sit down deep in the meat of it, at the top of the brainstem. But fish brains are more like Al Gore’s internet — a tube. That means scientists can get much easier access to the different key parts for study.  

When studying the midbrain activity of midshipman fish, Bass’ research team found that the male fish’s noises during foraging, nest-guarding duty and courtship each had their own distinct patterns that were observable in the fish’s activated periaqueductal gray (PAG) neurons. 

The flurry of electrical activity in the fish’s PAG neurons then triggers a brain response that makes the fish’s sound-related muscles start moving and more signal patterning starts happening in the midbrain. 

These signals “have frequency and amplitude components, and the fish string together sounds in different ways,” Bass said. “Maybe those sounds mean aggression or serve as a mating function – like you’re trying to attract a mate to a nest, which male midshipman do with their hum.”

Researchers also noted that PAG lesions, in particular, case mutism in humans — indicating the essential role the area plays in vocal communication. 

“Like mammals, the vocally active PAG region (of some fish’s brains) receives neuromodulator inputs. Inactivation of this region with lidocaine or dopamine effectively silences forebrain-evoked vocal output. Together, these studies suggest a critical role for a midbrain PAG region in vocal motor control between mammalian and non-mammalian vertebrate clades,” researchers said in the study. 

To model the acoustic patterns, though, researchers looked across the vocalizations of more than just fish and humans. Estrildid finch songs, Japanese quail calls, squirrel monkey caws and even the ultrasonic vocalizations of house mice were used for comparison in the study. Remarkably, despite the animals’ widely diverse types of vocal organs, researchers still found shared patterns of vocal-acoustic features. 

“Our findings now show that fish and mammals share functionally comparable periaqueductal gray nodes that can influence the acoustic structure of social context-specific vocal signals,” Bass said in his statement.

In explaining the significance of his work to our future understanding of the human brain, Bass compared the activity across the three main regions of our brains to the sweeping music of an orchestra. 

From our more instinctual and emotional limbic system in our forebrains, the music of our motivation moves into the midbrain where systems and patterns begin to light up, until the activity moves into our hindbrains and our muscles kick into action. Our goal with humans, he said, is to learn how that music is conducted across the brain’s systems. 

“There's no one part of your brain that really controls your behavior. It's really many different regions that have to be coordinated together in different manners,” he said. “We study the fish’s in part because their behaviors are simpler. And thereby we believe that we can really get at the fundamental characteristics that allow their brains to perform successful behaviors.”

It’s not just that the fish’s brains are tube-like and easier to fit an electrode or two into than our clunky helmet-shaped head meat. It’s not just that midshipman fish are easier to capture than actual sailors. It’s that the blood-and-electricity basics of human thought and behavior are still so profoundly complex and mysterious, that we need a foundational scientific understanding of how simpler brain systems work if we’re going to take advantage of technological progress in the neurosciences of tomorrow. 

“We can only hope the work that we’ve done will help others who study more complex brains found in mammals, for example, including primates and humans. The day is going to come — because of improvements in technology, microscopy and optical techniques — when we’re going to be able to see what these parts of the brain are doing in our own brains, when we’re doing different things,” Bass said. “I feel like the work we’re doing really helps set the foundation for that future kind of work. In the big picture, that’s what I believe.”