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Songbirds offer clues to highly practiced motor skills in humans

A songbird’s melodious sound may seem effortless, but its slurs are actually the result of rigorous training undergone in youth and maintained throughout adulthood. His tune has practically “crystallized” with maturity. The same control is observed in the motor performance of top athletes and musicians. Yet subtle variations in highly practiced skills persist in songbirds and humans. Now scientists think they know why.

Their discovery, reported in the journal Nature, suggests that natural variation is a built-in mechanism designed to allow the nervous system to explore various subtle options aimed at maintaining and optimizing motor skills in the face of variables such as aging and injury. .

Although the study was conducted on the adult male Bengal finch, a perky type that uses its song to woo females, the finding has implications, scientists say, for understanding how adult humans perform and retain well-learned motor skills. More broadly, the study provides information that could inform rehabilitation strategies for patients following strokes and other nervous system damage.

“Many neuroscientists have thought that the nervous system simply lacks the ability to control movement at a very precise level,” says lead author Evren Tumer, PhD, a postdoctoral fellow in lead author Michael’s lab. Brainard, PhD, UCSF assistant professor of physiology. “After all, we are not machines. But our study suggests that subtle variation may serve a purpose and help maintain motor skills.

“If a golfer had a perfect swing and all the conditions within him and in the outside environment were static, that wouldn’t be necessary,” he says. “But there are always changes – muscles get tired or cooler, neurons die or change with age. There is always a bit of change somewhere in the system. “To stay tuned,” Brainard explains, “the nervous system needs to constantly experiment, to continually correct deviations.”

The songbird tune is a complex skill, produced in a very stereotypical fashion from one performance to the next. Juveniles learn their song over a period of months, first memorizing their father’s melody and then, weeks later, embarking on a period of vocal exploration, during which they initiate their nascent interpretations while comparing them to the memory of their father’s melody, established in their neural circuits. This process, using auditory feedback, involves continuous adjustment of the bird’s melody, resulting in a stable, almost “crystallized” song.

Adult songbirds, on the other hand, rely on auditory feedback to maintain their song, and previous studies by Brainard have shown that if birds are deaf or receive garbled auditory feedback via computer intervention, their song fidelity declines. gradually deteriorates.

However, scientists don’t know if the modulation of adult bird song can be driven, predictably, by auditory feedback. In the current study, the team examined this possibility.

They used a computerized system to monitor small, natural variations in the pitch of targeted elements of birdsong, then delivered disruptive auditory feedback to a subset of vocalizations, or “syllables.” The disturbance took the form of a short burst of white noise – a “chh!-chh-chh!” his. Higher-pitched renders received a short burst of white noise, while lower-pitched versions were left undisturbed.

The response was almost immediate. Birds receiving white noise feedback quickly changed the pitch of their vocalizations to avoid the sound. The changes were limited precisely to the targeted syllable. “It was pretty dramatic,” Tumer says. “We were able to get the bird to sing a particular syllable with a higher pitch.”

“These data provide the first evidence that you can take this really stereotypical behavior that people have assumed crystallized and change it in some predetermined way.”

Notably, when the bursts of white noise were stopped, the pitch returned to its original range, indicating that the nervous system retained a representation of the original song and that there was “some urge to go back to it.” “.

The scientists also investigated whether a more dramatic remodeling of birdsong was possible. They explored this possibility by creating conditions in which the white noise exhaust forced the birds to make progressively greater pitch changes. Under these conditions, scientists were able to gradually make large changes to the point that syllables were produced in a range that did not overlap with the base range.

“It showed that you can make very big changes to this normally stereotypical behavior, but you have to do it gradually,” says Tumer. “This could have implications for rehabilitation strategies in humans.”

In support of the current findings, previous work by the team of Brainard and others found that when male songbirds sing alone, there is greater variability in their song than when they sing to females.

The theory, says Brainard, is that birds can afford to experiment, and therefore practice their tunes, when the pressure is released. This process, he suggests, does not occur at a conscious level. Rather, it is likely driven by neurochemicals released under varying circumstances which then act on a region of the nervous system known as the basal ganglia, which is essential for learning and maintaining songs.

“You can imagine,” says Tumer, who is also a fellow at the Keck Center for Integrative Neuroscience at UCSF, “that when courting a female bird — or stepping onto the green for the Masters golf tournament — neuromodulator systems would be more engaged than if the bird was on a lonely tree branch or the athlete on a sleepy Sunday afternoon golf game with friends.

The study was funded by the National Institutes of Health, the Sloan-Swartz Foundation and the McKnight Foundation.

UCSF is a leading university dedicated to defining global health through advanced biomedical research, graduate education in the life sciences and health professions, and excellence in patient care.

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