Researchers at the University of California, San Francisco, have discovered a new pathway in the human brain that processes the sounds of language. They found that auditory and speech processing occur in parallel (Cell).
For decades, scientists have thought that speech processing in the auditory cortex followed a serial pathway. It was thought that first, the primary auditory cortex processes simple acoustic information, such as frequencies of sounds. Then, an adjacent region, the superior temporal gyrus (STG), extracts more important features, like consonants and vowels, transforming sounds into meaningful words. But direct evidence for thishas been lacking.
Nine participants who underwent brain surgeries had arrays of small electrodes to cover their entire auditory cortex to collect neural signals for language and seizure mapping. The recordings were analysed to understand how the auditory cortex processes speech sounds.
When short phrases and sentences were played, the researchers found that some areas located in the STG responded as fast as the primary auditory cortex, suggesting that both areas started processing acoustic information simultaneously.
When the participants’ primary auditory cortex was stimulated with small electric currents, they experienced auditory hallucinations but were still able to clearly hear and repeat the said words. But when the STG was stimulated, the participants reported that they could hear people speaking, but couldn’t make out the words, the press release says.
