Summary: Speaking demands a tightly timed sequence of muscle commands. Long assumed to be organized mainly by Broca’s area, new research identifies the middle precentral gyrus (mPrCG) as a central hub for planning and executing those speech sequences.
Using direct brain recordings and brief electrical stimulation during surgery, researchers found that mPrCG activity rises with the complexity of syllable sequences and that disrupting this region produces speech errors. These findings reshape our understanding of speech-motor control and have potential implications for treating speech disorders and developing communication aids for people with paralysis.
Key Facts:
- The middle precentral gyrus (mPrCG) coordinates the ordering of speech sounds into words—a role previously ascribed largely to Broca’s area.
- Neural activity in the mPrCG increases in proportion to the phonemic and syllabic complexity of spoken sequences.
- Direct stimulation of the mPrCG disrupts complex speech sequences and produces errors resembling apraxia of speech.
Source: UCSF
Speaking clearly requires extraordinary coordination. Before a single syllable leaves your mouth, your brain translates intent into a precise, time-ordered set of motor commands that control dozens of muscles across the vocal tract. This process—speech-motor sequencing—ensures the right sounds occur in the right order and rhythm.
For more than a century, Broca’s area in the frontal lobe has been credited with much of this planning and coordination. However, new evidence from the University of California, San Francisco shows that a broader network of cortical regions is involved, with the mPrCG playing a central role.
The mPrCG lies in a region once thought to be primarily related to laryngeal control—adjusting pitch and tone. The new work suggests it does far more: it helps assemble individual speech sounds into fluent syllable and word sequences.
“This area of cortex plays a richer and more essential role than previously recognized,” said Edward Chang, MD, Chair of Neurosurgery at UCSF and senior author on the study. “It helps string speech sounds together into words, which is fundamental to fluent pronunciation.”
Published July 16 in Nature Human Behaviour, the study combines high-density cortical recordings and targeted stimulation in human patients to chart how the brain prepares and executes speech sequences. The results could inform how clinicians approach speech disorders, guide preservation of language function during neurosurgery, and advance neuroprosthetic systems that restore communication.
Beyond Broca’s area
Broca’s area, named after 19th-century physiologist Pierre Paul Broca, has long been associated with language production and comprehension. Yet over years of clinical observation and research, Chang and colleagues noticed speech-planning signals arising outside that classical region—particularly in the mPrCG.
A pivotal observation came from a patient who developed apraxia of speech—a disorder in which individuals know what they want to say but cannot coordinate the movements to say it—after surgical removal of a tumor in the mPrCG. Similar operations in Broca’s area did not produce the same deficit, suggesting a distinct and critical role for the mPrCG.
To investigate systematically, the research team studied 14 patients undergoing intracranial monitoring for epilepsy. Each patient had a thin electrode mesh placed on the cortical surface, allowing researchers to record neural activity during speech tasks without altering standard clinical care.
Participants read sequences of syllables and words on a screen and then produced them aloud after a short delay. Tasks ranged from simple repeated syllables like “ba-ba-ba” to more complex sequences such as “ba-da-ga” with multiple distinct sounds.
The recordings showed that mPrCG activity was not only present during production and auditory feedback but also sustained across the target presentation, delay, and execution phases. Crucially, sustained mPrCG activity scaled with sequence complexity and predicted how quickly participants initiated speech after the delay.
“The mPrCG works harder when sequences are more complex and then helps signal the muscles to carry out the plan,” explained Jessie Liu, PhD, a coauthor. “That pattern indicates the mPrCG is instrumental in organizing and launching speech sequences.”
Linking intention to action
The team also applied brief electrocortical stimulation to the mPrCG in five participants while they attempted preset syllable sequences. Stimulation had little effect on simple sequences, but with more complex sequences it produced speech errors mirroring apraxia—further supporting the mPrCG’s role in sequencing.
These results position the mPrCG as a critical node that translates linguistic intent into coordinated motor actions, acting as a bridge between higher-level language planning and the muscle commands needed for fluent speech.
“This shifts our view of speech production toward a distributed network centered on the mPrCG,” said Lingyun Zhao, PhD, a postdoctoral scholar on the project. “Understanding how this region contributes to sequencing gives us new avenues to study and treat speech impairments.”
Funding: This research was supported by the NIH (R01-DC012379) and philanthropic contributions.
About this language and neuroscience research news
Author: Robin Marks ([email protected])
Source: UCSF
Contact: Robin Marks – UCSF
Image: Image credit: Neuroscience News
Original Research: Closed access. “Speech sequencing in the human precentral gyrus” by Edward Chang et al., Nature Human Behaviour.
Abstract
Speech sequencing in the human precentral gyrus
Fluent speech requires assembling and preparing ordered motor plans for target speech sounds—a process termed speech-motor sequencing. Using high-density cortical recordings from 14 participants, the study measured neural responses while subjects produced utterances that varied in phonemic and syllabic complexity after reading a target and waiting through a delay period.
Researchers observed phasic activations linked to production and auditory feedback as well as sustained neural activity that persisted through target presentation, the delay, and execution phases. Sustained activity in the middle precentral gyrus correlated with sequence complexity and predicted reaction time. Electrocortical stimulation of this area produced speech disfluencies resembling apraxia. Together, the findings indicate that speech-motor sequencing is supported by a distributed cortical network with the mPrCG playing a central role.