Previous attempts to study the region's activities largely involved inserting a wire into the area, which could only reveal the signals at a limited number of spots. "This study is the first time that we could cover all of these areas simultaneously directly from the brain surface and study the transformation of sounds to words," Chang says. The participants also volunteered to have the recordings analyzed to understand how the auditory cortex processes speech sounds. For these procedures, arrays of small electrodes were placed to cover their entire auditory cortex to collect neural signals for language and seizure mapping. Over the course of seven years, Chang and his team have studied nine participants who had to undergo brain surgeries for medical reasons, such as to remove a tumor or locate a seizure focus. "So, we went into this study, hoping to find evidence for that - the transformation of the low-level representation of sounds into the high-level representation of words," says neuroscientist and neurosurgeon Edward Chang at the University of California, San Francisco. This is challenging, because the primary auditory cortex is located deep in the cleft that separates the frontal and temporal lobes of the human brain. Then, an adjacent region, called the superior temporal gyrus (STG), extracts features more important to speech, like consonants and vowels, transforming sounds into meaningful words.īut direct evidence for this theory has been lacking as it requires very detailed neurophysiological recordings from the entire auditory cortex with extremely high spatiotemporal resolution. It was thought that first, the primary auditory cortex processes the simple acoustic information, such as frequencies of sounds. For decades, scientists have thought that speech processing in the auditory cortex followed a serial pathway, similar to an assembly line in a factory. Sounds of language, upon reaching the ears, are converted into electrical signals by the cochlea and sent to a brain region called the auditory cortex on the temporal lobe.
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