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What do humans, macaques and guinea pigs have in common? A similar reaction of the brain to speech sounds. University of Pittsburgh Research

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The sounds of speech trigger similar responses and stimulate the same part of the brain in humans, macaques and guinea pigs, researchers at the University of Pittsburgh said. Recent research, published in the scientific journal eNeuro, may reveal more secrets about auditory processing deficits.

The brain’s responses to sound are called frequency-following responses (FFR). Scientists can record them with small electrodes placed on the scalp. They are most often used to quickly assess a child’s hearing ability and detect many potential speech and language disorders such as dyslexia and autism. However, this method has a serious disadvantage – it lacks detail.

FFR – what it is and what they are used for

“These tests can only tell us something is wrong – but we don’t know what exactly it is,” said research co-author Bharath Chandrasekaran of the School of Health Sciences and Rehabilitation, under the University of Pittsburgh. ‘Understanding the source and mechanism of FFR formation would allow the development of specific markers of speech disorders, which would be essential to improve clinical diagnosis of auditory processing deficits,’ he added.

FFRs – which the brain interprets and responds to – have the potential to complement hearing screening in newborns. If the baby’s brain responds to the sound being played, the neural pathway from the ear to the cortex is developed and functional.

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FFRs are also used to identify problems with interpreting environmental sounds, including speech. The closer the FFR profile is to that of the sound source, the greater the brain’s ability to process auditory processing. In turn, the greater the differences, the greater the risk of being diagnosed with an auditory deficit.

Reaction to a syllable from the Mandarin language

Until recently, scientists believed that FFRs are formed deep in the brainstem – the innermost structures near the base of the skull. They claimed that they spread outward, reaching the surface of the brain and even the scalp.

Meanwhile, by combining data from sensors placed on the scalp with records from electrodes placed inside the skull, researchers proved the theory wrong. They found that FFRs are generated not only in the brainstem, but also in the auditory cortex of the brain – the part of the temporal lobe that is responsible for processing sounds. Interestingly, the pattern of FFR generation is similar in all mammals.

The scientists took the syllable “yi” from the Mandarin language. They worked out four different tones of it and studied the brain response of English-speaking humans (who did not know the language), macaques and guinea pigs. It turned out that in both animal species the range of hearing and sensitivity was very similar to the results obtained in humans.

‘Identifying the similarities between animal and human FFRs will allow us to study sound-processing neural circuits in greater detail,’ said one of the authors of the Nike study, Gnanatej Gurindapalli. ‘This research will pave the way for new models of auditory processing in both typical and impaired auditory systems, and for diagnosing auditory deficits using simple, effective and non-invasive tools,’ he said.

Scientists say about 5-10 percent of Americans may be diagnosed with communication disorders. A better understanding of how hearing deficits manifest in the brain could offer hope for faster, more accurate and non-invasive diagnosis.

PAP / Maria Samczuk, Anna Zajkowska

Main photo source: Shutterstock



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