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How the Brain Regulates Vocal Pitch

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Credit: University of California, San Francisco

Whether it’s hitting a high note, delivering a punch line, or reading a bedtime story, the pitch of our voices is a vital part of human communication. Now, as part of their ongoing quest to produce a dynamic picture of neural function in real time, researchers funded by the NIH’s Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative have identified the part of the brain that controls vocal pitch [1].

This improved understanding of how the human brain regulates the pitch of sounds emanating from the voice box, or larynx, is more than cool neuroscience. It could aid in the development of new, more natural-sounding technologies to assist people who have speech disorders or who’ve had their larynxes removed due to injury or disease.

Our ability to speak is controlled in the sensorimotor cortex, part of the brain’s cerebral cortex. But how the sensorimotor complex orchestrates the physical process of human speech—from the movements of our lips to the vibrations in our larynxes—has remained unanswered until now.

While it can be awfully tricky trying to map such a complex process in the human brain, members of Edward Chang’s lab at the University of California, San Francisco’s Epilepsy Center are in an ideal position to do it. That’s because Chang, a neurosurgeon, regularly performs operations to remove seizure-inducing brain tissue from people with epilepsy.

Chang prepares for those operations by placing high-density arrays of tiny electrodes directly onto the surfaces of his patients’ brains. This method, known as electrocorticography, or ECoG, helps to identify the precise locations in the brain that trigger seizures. It’s also used to pinpoint other important brain areas, including those involved in language, to ensure they aren’t accidentally damaged during surgery.

In the first of two recent studies, this one led by graduate student Josh Chartier and published in the journal Neuron, Chang asked patients awaiting epilepsy surgery to read hundreds of carefully constructed sentences while those ECoG arrays were placed across the surfaces of their sensorimotor cortexes [2]. The study revealed for the first time how neurons coordinate the movements of nearly 100 muscles in the lips, tongue, jaws, and larynxes as people speak.

In the second study, led by graduate student Benjamin Dichter and just published in the journal Cell, the Chang team studied changes in vocal pitch by looking even deeper at the connections between the brain and larynx.  They started with the understanding that humans vary pitch, like tuning an instrument, by controlling the tension of muscles moving across vocal folds of the larynx. They also knew that our minds control these movements without us being aware of it.

Chang’s team asked 12 patient volunteers awaiting surgery to say a rather peculiar sentence: “I never said she stole my money.” They were then directed to change the meaning of the sentence by altering the pitch of their voices and emphasizing a specific word. For instance, “I never said she stole my money,” “I never said she stole my money,” and “I never said she stole my money.” (Try it now yourself—and note that you naturally tend to raise the pitch, as well as the volume, of the word being emphasized.) While the participants inflected their voices, the researchers used ECoG arrays to record neural activity across speech-processing areas of the brain.

Their studies showed neurons in the area of the sensorimotor cortex that controls the larynx activated each time the volunteers emphasized different words in a sentence. This area, called the dorsal laryngeal motor cortex, was most active when a speaker’s pitch reached its peak. Their studies also showed that a distinct group of neurons in dorsal laryngeal motor cortex control the sounds made by the larynx, while other neurons control variations in vocal pitch.

In a remarkable set of experiments in more than 80 patient volunteers, the researchers selectively stimulated neurons in the dorsal laryngeal motor cortex while recording activation of muscles in the larynx. They identified specific sites there that reliably flexed muscles in the larynx. In fact, 20 people responded to the brain stimulation by unintentionally making audible vocalizations!

The researchers also found similar brain activity when participants varied their pitch while singing. This indicates vocal pitch is controlled similarly in both speaking and singing. What’s more, those same brain areas lit up when participants listened silently to the sound of their own voices. The researchers suggest that might explain how people mimic speech, including matching another person’s pitch.

These human capacities for language, music, and song are not only fascinating, but they’re also fundamental to who we are and to our well-being. And they may have important therapeutic consequences too.  In fact, the NIH is engaged in a partnership with The Kennedy Center to explore the connections between music, health, and wellness called Sound Health. It kicked off last year with the Music and the Mind scientific workshop and concert that included opera’s extraordinary soprano Renee Fleming. The next Sound Health event is scheduled for September. You can bet that we’ll be talking about these two groundbreaking studies.

References:

[1] The Control of Vocal Pitch in Human Laryngeal Motor Cortex. Dichter BK, Breshears JD, Leonard MK, Chang EF. Cell. 2018 Jun 28;174(1):21-31.e9.

[2] Encoding of Articulatory Kinematic Trajectories in Human Speech Sensorimotor Cortex. Chartier J, Anumanchipalli GK, Johnson K, Chang EF. Neuron. 2018 Jun 6;98(5):1042-1054.e4. doi: 10.1016/j.neuron.2018.04.031.

Links:

The BRAIN Initiative (NIH)

Sound Health (NIH)

Edward Chang (University of California, San Francisco)

NIH Support: Office of the Director; National Institute of Neurological Disorders and Stroke