A new study on white-throated sparrows suggests that a bird listening to birdsong may experience some of the same emotions as a human listening to music.
"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," said 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.
"Birdsong is a signal. 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," Maney said.
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 said.
"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," she added.
A major limitation of the study, Earp noted, is that many of the regions that respond to music in humans are cortical, and they do not have clear counterparts in birds.
The study was published in Frontiers of Evolutionary Neuroscience.