A network of volume settings in the brain, that can choose to silence or amplify the sounds we make and hear has been discovered in a new study.
The study from the University of California, Berkeley, tracked the electrical signals emitted from the brains of hospitalized epilepsy patients. They discovered that neurons in one part of the patients' hearing mechanism were dimmed when they talked, while neurons in other parts lit up.
Activity in the auditory cortex when we speak and listen is amplified in some regions of the brain and muted in others.
Their findings offer new clues about how we hear ourselves above the noise of our surroundings and monitor what we say.
"We used to think that the human auditory system is mostly suppressed during speech, but we found closely knit patches of cortex with very different sensitivities to our own speech that paint a more complicated picture," said Adeen Flinker.
"We found evidence of millions of neurons firing together every time you hear a sound right next to millions of neurons ignoring external sounds but firing together every time you speak," Flinker added.
Flinker theorizes that tracking our own speech is important for language development, monitoring what we say and adjusting to various noise environments.
He noted that people with schizophrenia have trouble distinguishing their own internal voices from the voices of others, suggesting that they may lack this selective auditory mechanism. The findings may be helpful in better understanding some aspects of auditory hallucinations, he said.
Researchers instructed the patients to perform such tasks as repeating words and vowels they heard, and recorded the activity. In comparing the activity of electrical signals discharged during speaking and hearing, they found that some regions of the auditory cortex showed less activity during speech, while others showed the same or higher levels.
"This shows that our brain has a complex sensitivity to our own speech that helps us distinguish between our vocalizations and those of others, and makes sure that what we say is actually what we meant to say," Flinker said.
Their findings are published today (Dec. 8, 2010) in the Journal of Neuroscience.