A new study published in the journal eNeuro has found that speech sounds elicit similar neural responses and stimulate the same brain areas in humans, macaques, and guinea pigs. These findings may help better understand and diagnose auditory processing deficits.
The brain’s responses to sounds (“frequency following responses,” or FFRs) can be recorded by small electrodes placed on the scalp, and are generally used by clinicians to quickly asses infants’ hearing capacities in order to find out whether they may develop disorders such as dyslexia or autism.
If the infants’ brains produce electrical responses to sounds played through tiny headphones, their neural pathways connecting the ears to the high-level information processing areas of the brain are functional. However, until recently, this method lacked specificity.
“These tests can only tell us that something is off – but we don’t know what that ‘off’ is,” said study co-author Bharath Chandrasekaran, a professor of Auditory Cognitive Neuroscience at the University of Pittsburg’s School of Health and Rehabilitation Sciences.
“Understanding the source and mechanism of FFR generation would allow for the development of specific markers of speech impairments, which would be instrumental in improving clinical diagnostics of auditory processing deficits.”
Until recently, scientists thought that FFRs arise deep inside the brain stem. However, by combining electroencephalographic recordings from the scalp with recordings from electrodes placed inside the skull, the researchers found that FFRs are generated also in the auditory cortex of the brain, only a few centimeters away from the skull surface. Moreover, they appeared to be similar across mammals such as humans, monkeys, and guinea pigs.
“Recognizing the similarities between animal and human FFRs will allow us to study neural circuitry of sound processing in much greater detail,” said study lead author Nike Gnanateja Gurindapalli, a postdoctoral fellow at the University of Pittsburgh. “These explorations will further pave the way for new models of auditory processing in both typical and impaired auditory systems, which can eventually be used to infer auditory deficits using simple and effective non-invasive tools in the clinic.”
Since FFRs were traditionally thought to be passively generated outside the cortex, scientists did not typically account for a person’s attention and alertness during FFR recordings. This new discovery will change the way FFRs are collected and interpreted and will open pathways for the development of better biomarkers of auditory processing deficits, leading to faster, more accurate, and non-invasive diagnostics.