Recent advancements in brain mapping are revolutionizing our understanding of human speech and auditory hallucinations in schizophrenia. A groundbreaking study reveals the critical role of auditory corollary discharge signals, which begin and end in two key subregions of the brain’s cortex.
These signals bridge the motor cortex, responsible for voluntary movements like speech, and the auditory cortex, which governs hearing.Evolutionary Insight into Brain SignalsAuditory corollary discharge signals play a vital role in distinguishing one’s own voice from external sounds, an evolutionary adaptation seen across species.
In animals, these electrical signals help crickets differentiate their mating chirps, enable songbirds to perform mating calls, and allow bats to navigate using sound reverberations. Similarly, in humans, these signals suppress background noise, ensuring clear communication.However, disruptions in this system may cause auditory hallucinations in individuals with schizophrenia, who struggle to discern internal voices from external sounds.
Such disturbances are also linked to speech disorders like stuttering, making this research pivotal for understanding these conditions.Breakthrough in Brain MappingThe study, led by researchers at NYU Langone Health and NYU Tandon School of Engineering, focused on the origins of auditory corollary discharge signals in the motor cortex.
By conducting experiments with eight epilepsy patients undergoing surgery, the team was able to overcome challenges in tracking brain activity during speech.The research identified the ventral motor cortex, specifically the precentral gyrus, as the starting point for these signals. From here, the signals travel to the superior temporal gyrus in the auditory cortex, lasting approximately 120 milliseconds.
These findings solve a long-standing mystery about the brain circuits involved in speech.Implications for Schizophrenia and Speech Disorders”Our study provides the first direct evidence of motor cortex circuits enabling us to remain aware of our surroundings while speaking,” said Amirhossein Khalilian-Gourtani, Ph.D., lead investigator.
The research also sheds light on the origins of auditory hallucinations in schizophrenia, suggesting they stem from disrupted signals between the motor and auditory cortices.Neuroscientist Adeen Flinker, Ph.D., noted that individuals with schizophrenia might struggle to dissociate their own voice from external stimuli, a theory supported by the study’s findings.Cutting-Edge Research TechniquesTo achieve these results, researchers recorded over 3,200 instances of brain activity during speech experiments.
Using advanced computer models, they tracked the brain’s electrical responses as patients completed tasks like repeating words, finishing sentences, and describing images.This meticulous approach allowed patients to remain engaged with their surroundings while focusing on their speech, offering unparalleled insight into the brain’s corollary discharge mechanism.A Step Forward in NeurosciencePublished in the Proceedings of the National Academy of Sciences and currently available on bioRxiv, this study marks a significant leap in neuroscience. By uncovering the intricate brain circuits involved in speech and auditory processing, researchers have laid the groundwork for better understanding and treating conditions like schizophrenia and speech disorders.
This breakthrough not only enhances our knowledge of human speech but also opens new avenues for therapeutic interventions targeting auditory hallucinations and communication challenges.
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