A bird listening to birdsong may experience some of the same emotions as a human listening to music, suggests a new study on white-throated sparrows, published in Frontiers of Evolutionary Neuroscience.
"We found that the same neural reward system is activated in female birds in the breeding state that are listening to male birdsong, and in people listening to music that they like," says Sarah Earp, who led the research as an undergraduate at Emory University.
For male birds listening to another male's song, it was a different story: They had an amygdala response that looks similar to that of people when they hear discordant, unpleasant music.
The study, co-authored by Emory neuroscientist Donna Maney, is the first to compare neural responses of listeners in the long-standing debate over whether birdsong is music.
"Scientists since the time of Darwin have wondered whether birdsong and music may serve similar purposes, or have the same evolutionary precursors," Earp notes. "But most attempts to compare the two have focused on the qualities of the sound themselves, such as melody and rhythm."
Earp's curiosity was sparked while an honors student at Emory, majoring in both neuroscience and music. She took "The Musical Brain" course developed by Paul Lennard, director of Emory's Neuroscience and Behavioral Biology program, which brought in guest lecturers from the fields of neuroscience and music.
"During one class, the guest speaker was a composer and he said that he thought that birdsong is like music, but Dr. Lennard thought it was not," Earp recalls. "It turned into this huge debate, and each of them seemed to define music differently. I thought it was interesting that you could take one question and have two conflicting answers that are both right, in a way, depending on your perspective and how you approach the question."
As a senior last year, Earp received a grant from the Scholars Program for Interdisciplinary Neuroscience Research (SPINR), and a position in the lab of Maney, who uses songbirds as a model to study the neural basis of complex learned behavior.
When Earp proposed using the lab's data to investigate the birdsong-music debate, Maney thought it was a great idea. "Birdsong is a signal," Maney says. "And the definition of a signal is that it elicits a response in the receiver. Previous studies hadn't approached the question from that angle, and it's an important one."
Earp reviewed studies that mapped human neural responses to music through brain imaging.
She also analyzed data from the Maney lab on white-throated sparrows. The lab maps brain responses in the birds by measuring Egr-1, part of a major biochemical pathway activated in cells that are responding to a stimulus.
The study used Egr-1 as a marker to map and quantify neural responses in the mesolimbic reward system in male and female white-throated sparrows listening to a male bird's song. Some of the listening birds had been treated with hormones, to push them into the breeding state, while the control group had low levels of estradiol and testosterone.
During the non-breeding season, both sexes of sparrows use song to establish and maintain dominance in relationships. During the breeding season, however, a male singing to a female is almost certainly courting her, while a male singing to another male is challenging an interloper.
For the females in the breeding state every region of the mesolimbic reward pathway that has been reported to respond to music in humans, and that has a clear avian counterpart, responded to the male birdsong. Females in the non-breeding state, however, did not show a heightened response.
And the testosterone-treated males listening to another male sing showed an amygdala response, which may correlate to the amygdala response typical of humans listening to the kind of music used in the scary scenes of horror movies.
"The neural response to birdsong appears to depend on social context, which can be the case with humans as well," Earp says. "Both birdsong and music elicit responses not only in brain regions associated directly with reward, but also in interconnected regions that are thought to regulate emotion. That suggests that they both may activate evolutionarily ancient mechanisms that are necessary for reproduction and survival."
A major limitation of the study, Earp adds, is that many of the regions that respond to music in humans are cortical, and they do not have clear counterparts in birds. "Perhaps techniques will someday be developed to image neural responses in baleen whales, whose songs are both musical and learned, and whose brain anatomy is more easily compared with humans," she says.
Earp, who played the viola in the Emory orchestra and graduated last May, is now a medical student at the Cleveland Clinic.
So what music makes her brain light up? "Stravinsky's 'Firebird' suite," Earp says.
- Sarah E. Earp, Donna L. Maney. Birdsong: Is It Music to Their Ears? Frontiers in Evolutionary Neuroscience, 2012; 4 DOI: 10.3389/fnevo.2012.00014
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