It's a long way from the dull hums of the amorous midshipman fish to the strains of a Puccini aria—or, alas, even to the simplest Celine Dion melody. But the neural circuitry that led to the human love song—not to mention birdsongs, frog thrums and mating calls of all manner of vertebrates—was likely laid down hundreds of millions of years ago with the hums and grunts of the homely piscis.
By mapping the developing brain cells in newly hatched fish larvae and comparing them to other species, Cornell University professor of neurobiology and behavior, Andrew H. Bass, found that the neural network behind sound production in modern vertebrates can be traced back through evolutionary time to an era long before the first animals ventured onto dry land.
Bass used fluorescent dyes to identify distinct groups of neurons in the brains of the larvae of midshipman fish, a species known for the loud humming sounds adult males generate with their swim bladders to attract females to their nests.
Bass and his collaborators, Edwin Gilland of Howard University and Robert Baker of New York University, observed clusters of cells in the larvae's developing hindbrain as they formed connections and grew into the networks that control vocalization in mature fish.
They found that the neurons in a compartment of the hindbrain known as rhombomere 8, which are thought to control pattern generation in vocalizing vertebrates, give rise to the circuitry of the vocal motor nucleus—the system behind the fishes' hums.
Comparing that system to the neural circuitry behind vocalizations of amphibians, birds, reptiles and mammals, including primates, Bass found that while the networks vary in complexity, their fundamental attributes have stayed essentially the same throughout time, even as some animals have gone on to develop elaborate physical structures for vocal communications.
Knowing the neuroanatomy behind vocalization in such a broad range of species also provides a framework for neuroscientists and evolutionary biologists to better understand how animals have adapted sound production to social settings and survival strategies, Bass said.
The research was supported by the National Science Foundation and the National Institutes of Health. It was published in the July 18 issue of the journal Science.
—Lauren Gold/Cornell University
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