The midbrain of the vocal Plainfin midshipman fish, sometimes called the “singing fish of California”, plays an important role in initiating and patterning the trains of sounds used in vocal communication.

It turns out the midbrain of these fish can be a useful model for how mammals and other vertebrates, including humans, control vocal expressions, according to research on behavior conducted by Cornell University and published in Nature Communications.

We have evidence that this part of the brain, the midbrain, is important for voice signaling, said lead author Andrew Bass, the Horace White Professor of Neurobiology and Behavior at Cornell’s College of Arts and Sciences. It’s a region of the brain shared by all vertebrates, whether we’re talking about a fish, a bird, or a person, and it’s crucial for the pattern and selection of sound.

The Plainfin midshipman fish’s phrasing takes the form of grunts, groans, and hums when males seek mates or defend against enemies, Bass explains. To the human ear, the hum might sound like a single note from a French horn or foghorn.

Though they live offshore in northern California and the northwest Pacific during fall and winter, they head to shallow intertidal zones to spawn in late spring and summer. They are good parents and will guard hundreds of unhatched eggs that grow into free-swimming larvae sheltered under rocky shelters.

On low tide, people sitting atop the shoreline on a quiet summer evening will report the constant conversational humming of a chorus of singing male Plainfin midshipmen.

While science knew mammals and other vertebrates emit sounds and vocalize to communicate behaviors, the midbrain responsible for initiating acoustic features—like the hums in these fish or the formation of convincing phrases in humans—had largely remained unexplored.

Eric R. Schuppe, a former Cornell postdoctoral researcher in Bass’s lab who is now a postdoctoral researcher at the University of California, San Francisco, led the research.

Bass, Schuppe, and other lab members discovered the midbrain’s gray neurons are activated in distinct patterns by males during courtship calling, foraging, and nest guarding. The group confirmed the gray neurons evoke output to muscles managing sound and vocal characteristics of courtship calling as well as showing patterns in other call types.

The midbrain-modeled communication signals have frequency and amplitude components, and the fish string the sounds together in different ways, explains Bass. Perhaps those sounds mean aggression or serve a mating function, like when attempting to lure a mate to a nest—something male Plainfin midshipmen do with their humming.

The human brain has a helmet shape, and the midbrain sits at the top of the brainstem. Fish brains have a more tube-like shape, making them a more accessible model for experimental study, says Bass.

Our findings now demonstrate that fishes and mammals share functionally comparable gray nodal regions that can influence the acoustic structure of context-specific social vocal signals, he stated.

Male midshipman fish (Porichthys notatus), like the one in this video, can drone on for hours luring females to mate. A night of humming starts with a cue from melatonin, a hormone that can make people sleepy, researchers at Cornell University have found

Bass noted that in humans, this research provides clues about what happens if the human midbrain is damaged. He suggested this research can help us understand how dysfunction of the human midbrain may cause a person to not communicate or become mute.

Only in recent years have neuroscientists studying social communication paid more attention to the midbrain, Bass explains. It’s an important hub connected to the cortex, basal ganglia, amygdala, and hypothalamus. In this way, it acts as a gateway for these sources of executive functions to more directly activate muscles underlying behavioral actions.

Says Bass: The midbrain is an amazing part of the brain because it underscores how essential it is—if you’re a vertebrate—to have the ability to produce audible communication signals. And that’s the point.


Sources

Cornell University | Schuppe, E.R., Ballagh, I., Akbari, N. et al. Midbrain node for context-specific vocalisation in fish. Nat Commun 15, 189 (2024). doi.org/10.1038/s41467-023-43794-y


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