Summary: Researchers have mapped how the brain suppresses background noise during speech by tracing fast electrical signals between the motor and auditory cortices. These millisecond-long transmissions—called auditory corollary discharge—originate in the ventral motor cortex (precentral gyrus) and travel to the auditory cortex’s superior temporal gyrus, helping the brain distinguish self-generated speech from external sounds.
This mechanism lets people remain aware of external acoustic cues while speaking and is disrupted in conditions such as schizophrenia, where it can contribute to auditory hallucinations. The findings clarify the neural circuitry of speech processing and could guide development of noninvasive diagnostic tests and interventions for speech-related disorders.
Key Facts:
- Auditory corollary discharge signals help the brain distinguish one’s own voice from background sounds.
- These signals travel from the motor cortex to the auditory cortex in tens to hundreds of milliseconds.
- Disruption of this circuit is implicated in auditory hallucinations and may play a role in stuttering.
Source: NYU Langone
Voice experiments in people with epilepsy revealed the circuit of electrical signals that enables the auditory cortex to filter out background noise from an individual’s own voice.
Animals and humans rely on the ability to separate self-generated vocalizations from external sounds. This distinction supports threat detection, social communication, and navigation in complex environments. Comparable corollary discharge mechanisms occur in many species—for example, crickets distinguishing their mating chirps from others, songbirds coordinating vocal sequences, and bats using echoes to interpret surroundings.
In humans, when this fast back-and-forth signaling between motor and auditory regions is disrupted, people may struggle to differentiate internal from external sounds. Such disturbances are considered a hallmark of auditory hallucinations in schizophrenia, where patients report hearing voices that they cannot identify as self-generated. Similar mechanisms have been proposed in speech fluency disorders such as stuttering.
While animal studies and prior mammalian research had implicated the motor cortex in generating corollary discharge, pinpointing the exact origins and timing in the human brain proved challenging. Practical obstacles include safely recording brain activity while people are awake and speaking and the computational complexity of analyzing such high-resolution data.
To address these challenges, an interdisciplinary team at NYU Langone Health, its Neuroscience Institute, and NYU’s Tandon School of Engineering conducted detailed voice experiments with eight adults undergoing neurosurgical monitoring for epilepsy. The patients volunteered to perform word-based tasks while clinicians recorded electrocorticographic signals from intracranial electrodes placed to localize seizure foci.
Published online in the Proceedings of the National Academy of Sciences (PNAS), the study reports that the corollary discharge source localizes to the ventral portion of the motor cortex—specifically the precentral gyrus—before speech articulation. These discharge events averaged about 120 milliseconds and propagated across the precentral gyrus into the neighboring auditory cortex region, the superior temporal gyrus.
“Our study resolves a long-standing question by providing direct evidence of motor cortex circuits that generate corollary discharge in human speech,” said lead investigator Amirhossein Khalilian-Gourtani, PhD, a postdoctoral research fellow in the Department of Neurology at NYU Grossman School of Medicine. The team’s findings identify a reproducible neural source and timing for the discharge that predicts the degree of auditory cortex suppression during speech.
Senior investigator Adeen Flinker, PhD, an associate professor in the Department of Neurology at NYU Grossman School of Medicine and NYU Tandon School of Engineering, added that the results offer specific mechanistic insight into schizophrenia: disrupted corollary discharge between motor and auditory cortices could explain why some individuals cannot dissociate their own voice from external stimuli.
During the study, researchers collected more than 3,200 intracranial recordings while patients completed over 200 probes and repeated speech tasks during planned breaks in surgery. Tasks included listening to and repeating single words (for example, “balloon”), completing sentences with the same word, and describing images using the target word. Each task required subjects to maintain attention to visual and acoustic context while suppressing background cues to produce the same spoken response.
The team combined the intracranial recordings with a computational connectivity analysis based on Granger causality to map directed neural communications. This approach allowed them to identify a consistent, pre-articulation corollary discharge originating in ventral motor cortex and influencing auditory cortex suppression—a key component of normal speech motor control.
Looking ahead, investigators plan to test whether the corollary discharge circuit becomes active immediately before stimulation-induced hallucinations and to collaborate with psychiatrists on noninvasive methods to assess this signal in people with schizophrenia.
Funding: Support for the study came from National Science Foundation grant HS-1912286 and National Institutes of Health grants R01NS109367 and R01NS115929.
Key contributors from NYU Langone and NYU Tandon include Amirhossein Khalilian-Gourtani, Adeen Flinker, Ran Wang, Xupeng Chen, Leyao Yu, Patricia Dugan, Daniel Friedman, Werner Doyle, Orrin Devinsky, and Yao Wang.
About this auditory neuroscience and schizophrenia research news
Author: David March
Source: NYU Langone
Contact: David March – NYU Langone
Image: The image is credited to Neuroscience News
Original Research: Closed access. “A Corollary Discharge Circuit in Human Speech” by Amirhossein Khalilian-Gourtani et al. PNAS
Abstract
A Corollary Discharge Circuit in Human Speech
When we vocalize, the brain must distinguish self-generated sounds from external ones. Corollary discharge signals support this differentiation in animals; in humans, the precise origin and timing of these signals were previously unclear. Electrocorticographic recordings in neurosurgical patients combined with a Granger causality–based connectivity framework reveal a reproducible corollary discharge source in the ventral speech motor cortex preceding articulation. This discharge predicts the magnitude of auditory cortex suppression during speech. These results identify the human corollary discharge source and timing, with implications for speech motor control and the neural basis of auditory hallucinations in psychosis.