How Tiny Monkeys Can Help Us Understand How We Process the Sound of Our Own Voices

By Jeni Baker


Dr. Steven Eliades’s marmoset studies could one day help to improve therapies for certain speech and voice problems.

Duke Head and Neck Surgery & Communication Sciences associate professor Steven J. Eliades, MD, PhD, and his research team focus on the neural basis of vocal communication.

Dr. Eliades works with a colony of 31 marmosets. The tiny, non-human primates are chatty and social, with complex brain structures, advanced motor skills and immune systems, metabolic similarities, and other characteristics that make marmosets more similar to humans than other commonly used animal models are.

Dr. Eliades and his group are working to learn more about a foundational piece of knowledge that could someday help to improve therapies for people with certain types of voice disorders and speech problems.

How Do People’s Brains Make Sense of Their Voices?

“Our current work with marmosets is primarily focused on understanding how human beings are able to process the sound of our own voices — and how we then use this information to help us control the sounds we produce,” says Dr. Eliades.

“This work is most directly relevant to voice disorders — and perhaps less so to speech — since animals lack the fine control and complex combinations that make up human speech and language.”

Dr. Eliades reports that his team’s most significant finding so far is that “the brain uses very different mechanisms to process the sound of our own voice when compared to sounds that we are just listening to,” he says.

“Mounting evidence suggests that the area responsible for initiating or controlling our vocalization sends information to our auditory sensory areas that tell those structures what we expect to hear of ourselves. We then compare this sensory prediction to what we actually hear, which allows our brain to calculate an ‘error signal,’” Dr. Eliades explains.

“There is also now evidence that the brain can use this error information to compensate and change the vocalizations we produce. Importantly, this brain circuit for vocal self-monitoring seems to be evolutionarily ancient; we see it in both marmosets and humans.”

A goal of the team’s marmoset research is to translate key findings like these into more effective therapies for people with brain-related voice disorders and speech problems.

“My hope is that understanding these brain mechanisms will lead to a number of new therapies that help the communication of patients with speech and voice disorders,” says Dr. Eliades.

“This may include novel behavioral therapies; non-invasive devices that help patients monitor their speech (or ignore the sound of their own voices); or neurotechnologies such as speech prostheses that interpret or stimulate the brain to help in communication.”

His group’s findings might also one day apply to certain stroke-related speech issues.

“Recent work by other research groups has shown that the sorts of brain circuits and behaviors we study in marmosets may also be affected in some stroke patients,” Dr. Eliades says. 

“The implications are a bit fuzzy, but some patients with classic left-hemisphere language-affecting strokes also show abnormal voice control and abnormal brain connectivity, even in the other side of the brain. Even less is known about strokes in the right hemisphere, because they often cause more subtle language deficits.”

More Marmoset Research

Dr. Eliades says he and his team plan to extend their findings to better understand some of the deeper cellular and circuit mechanisms underlying vocal self-monitoring.

“For example, if our brain is using predictions to make these sorts of error comparisons, we want to find out what happens if the error itself becomes predictable,” he says. “Because they can be related to learning and brain plasticity — and therefore rehabilitation approaches — these are the sort of questions that can lead to novel therapies.”

The group also has begun some brain-related marmoset studies that could lead to a better understanding of stroke-related problems with speech.  

“We’re starting research to look at frontal brain areas, including marmoset homologues of Broca’s area — a region of the left hemisphere of the frontal cortex that affects speech production — to better understand the evolutionary origins of human speech,” explains Dr. Eliades.

“There are some interesting disconnects between what is known about the frontal brain during animal communication and what is seen during human strokes. Understanding these differences — as well as any evolutionarily older brain circuits — may give us some novel insights and approaches for stroke treatments in the future.”

To schedule an appointment with a Duke Head and Neck Surgery & Communication Sciences expert, call 919-439-1870.

To refer a patient, call 800-633-3853 or use DukeMedLink.