A songbirds’ vocal muscles work like those of human speakers and singers, finds a study recently published in the Journal of Neuroscience. The research on Bengalese finches showed that each of their vocal muscles can change its function to help produce different parameters of sounds, in a manner similar to that of a trained opera singer.
“Our research suggests that producing really complex song relies on the ability of the songbirds’ brains to direct complicated changes in combinations of muscles,” says Samuel Sober, a biologist at Emory University and lead author of the study. “In terms of vocal control, the bird brain appears as complicated and wonderful as the human brain.”
Pitch, for example, is important to songbird vocalization, but there is no single muscle devoted to controlling it. “They don’t just contract one muscle to change pitch,” Sober says. “They have to activate a lot of different muscles in concert, and these changes are different for different vocalizations. Depending on what syllable the bird is singing, a particular muscle might increase pitch or decrease pitch.”
Previous research has revealed some of the vocal mechanisms within the human “voice box,” or larynx. The larynx houses the vocal cords and an array of muscles that help control pitch, amplitude and timbre.
Instead of a larynx, birds have a vocal organ called the syrinx, which holds their vocal cords deeper in their bodies. While humans have one set of vocal cords, a songbird has two sets, enabling it to produce two different sounds simultaneously, in harmony with itself.
“Lots of studies look at brain activity and how it relates to behaviors, but muscles are what translates the brain’s output into behavior,” Sober says. “We wanted to understand the physics and biomechanics of what a songbird’s muscles are doing while singing.”
The researchers devised a method involving electromyography (EMG) to measure how the neural activity of the birds activates the production of a particular sound through the flexing of a particular vocal muscle.
The results showed the complex redundancy of the songbird’s vocal muscles. “It tells us how complicated the neural computations are to control this really beautiful behavior,” Sober says, adding that songbirds have a network of brain regions that non-songbirds do not.
The study was co-authored by Kyle Srivastava, a graduate student of the Emory and Georgia Tech Biomedical Engineering Doctoral Program, and Coen Elemans, a biologist from the University of Southern Denmark and a former visiting professor at Emory, funded by the Emory Institute for Quantitative Theory and Methods and the National Institutes of Health.
Source: Carol Clark – Emory University
Image Source: The image is in the public domain
Original Research: Abstract for “Multifunctional and Context-Dependent Control of Vocal Acoustics by Individual Muscles” by Kyle H. Srivastava, Coen P.H. Elemans, and Samuel J. Sober in Journal of Neuroscience. Published online October 21 2015 doi:10.1523/JNEUROSCI.3610-14.2015
Multifunctional and Context-Dependent Control of Vocal Acoustics by Individual Muscles
The relationship between muscle activity and behavioral output determines how the brain controls and modifies complex skills. In vocal control, ensembles of muscles are used to precisely tune single acoustic parameters such as fundamental frequency and sound amplitude. If individual vocal muscles were dedicated to the control of single parameters, then the brain could control each parameter independently by modulating the appropriate muscle or muscles. Alternatively, if each muscle influenced multiple parameters, a more complex control strategy would be required to selectively modulate a single parameter. Additionally, it is unknown whether the function of single muscles is fixed or varies across different vocal gestures. A fixed relationship would allow the brain to use the same changes in muscle activation to, for example, increase the fundamental frequency of different vocal gestures, whereas a context-dependent scheme would require the brain to calculate different motor modifications in each case. We tested the hypothesis that single muscles control multiple acoustic parameters and that the function of single muscles varies across gestures using three complementary approaches. First, we recorded electromyographic data from vocal muscles in singing Bengalese finches. Second, we electrically perturbed the activity of single muscles during song. Third, we developed an ex vivo technique to analyze the biomechanical and acoustic consequences of single-muscle perturbations. We found that single muscles drive changes in multiple parameters and that the function of single muscles differs across vocal gestures, suggesting that the brain uses a complex, gesture-dependent control scheme to regulate vocal output.
“Multifunctional and Context-Dependent Control of Vocal Acoustics by Individual Muscles” by Kyle H. Srivastava, Coen P.H. Elemans, and Samuel J. Sober in Journal of Neuroscience. Published online October 21 2015 doi:10.1523/JNEUROSCI.3610-14.2015