Study finds human auditory system more intricate than previously presumed

A UC Berkeley graduate student’s ongoing research on the human auditory system has given more insight into how the system is wired — that it is made of a network of volume settings that can selectively silence and amplify the sounds people make and hear.

Previously, scientists believed the auditory system was not as active when people hear themselves speak, according to Adeen Flinker, who is conducting the research. However, through his work he said he found that the system is more intricate, with subregions that are specific to what a person hears.

To conduct the study, which was published in December, Flinker said he and his fellow researchers studied patients who have epilepsy. He worked with neurologists from UC San Francisco and Johns Hopkins University, who were responsible for monitoring and treating the patients as the electrical activity in their brain was recorded.

Though more research is needed, Flinker said he hoped the findings from his study could eventually be used to aid those with malfunctioning auditory systems, such as those who suffer from schizophrenia or who have had strokes.

“People with strokes sometimes have deficits where they understand everything but can’t say anything,” he said.

But reaching this goal is still a “work in progress,” according to Flinker, who said more research needs to be done before he can draw any definite conclusions and that this study was one of many being conducted.

Edward Chang, a neurosurgeon from UCSF, was one of several doctors who collaborated with the researchers and whose patients were used as subjects. He said that as the research was conducted, his main task was data acquisition and looking after his patients and that he thought the findings on the auditory cortex and its function were “groundbreaking.”

The patients’ brain activity was recorded for only a few minutes as they performed a few simple tasks, such as repeating vowels and words, Flinker said. He then looked at the brain’s responses to auditory feedback, comparing the difference in activity from when the person was speaking to when the person was listening to someone else.

The researchers did discover a distinct suppression in cortical activities when subjects heard themselves speaking.

Robert Knight, a co-author of the study and the director of the Helen Wills Neuroscience Institute at UC Berkeley, where Flinker works, said the reason for this suppression is that people are already aware of what they’re going to say. A copy of their action, or an efference copy, is transmitted to the portion of the brain that receives sensory input.

“It’s a way to prime the brain area about self-initiated acts,” Knight said, adding that the purpose of this mechanism was energy conservation.

However, Flinker said though many regions of the cortex were suppressed, there were many that were not, which indicates a “varying degree of suppression.”

Though the research has been done by many people in different fields, Flinker said he still sees the ongoing research as an effort that will require the collaboration of many different people.

“A fundamental part of writing and planning an article is understanding what is known, what other people did, to see if you can add to that,” Flinker said. “And hopefully, that piece of information can help other researchers to make things better for our knowledge and help people with strokes and people with schizophrenia.”