Daniel Polley
BOSTON—It’s long been known that transitory hearing loss in childhood can have permanent effects on a child’s development. The temporary conductive hearing problems that so many children suffer due to ear infections may interfere with their ability to learn and develop communication skills, with results that often continue long after the hearing loss has ended.
However, recent research with animal subjects suggests that short-term hearing loss may have an even more pernicious effect on children. Even when their hearing thresholds return to normal, more subtle aspects of their hearing, including the ability of their two ears to function binaurally, may always be impaired because of their “short-term” hearing loss.
In an article published September 30 in Nature Communications, Daniel Polley, PhD, a hearing scientist at Massachusetts Eye and Ear/Harvard Medical School’s Eaton-Peabody Laboratories of Auditory Physiology, and two co-authors report that temporary hearing loss in childhood may lead to persistent hearing deficits. That is because the processing of sound in the brain is shaped by early experience.
In their research, Polley and his colleagues John H. Thompson and Wei Guo induced a brief, reversible hearing loss in mice at key milestones in their cortical development. By doing so, they identified two critical periods occurring after hearing onset that regulate the maturation of coordinated binaural sound representations. Their work may eventually lead to a better understanding of when in children’s development it is most critical for them to have normal hearing.
In an interview with Massachusetts Eye and Ear Infirmary, Polley explained, “The goal of this study was to mimic the moderate, short-term hearing loss that can accompany ear infections in human infants and then study how and when the encoding of auditory signals was disrupted in the brains of developing mice.”
The scientists found that creating a temporary hearing loss one day after hearing had begun disrupted the basic alignment of sound frequency selectivity in the mouse cortex. They also found that the same manipulation initiated just a few days later interfered with the neural computation of loudness differences between the ears.
If sensory experience is degraded during these critical periods in a young child’s life, as occurs with conductive hearing loss accompanying otitis media, a common and often chronic type of ear infection, the brain’s representation of the sensory world can be distorted in a specific and enduring way, even after the physical deficit in the ear has been corrected.
Polley said, “These findings demonstrate that brief bouts of asymmetric hearing loss during very specific points in postnatal development can have a lasting effect on brain circuits that compare and integrate the sound waves that enter each ear.” He added, “Though our study was conducted in an animal model, these data support a growing body of work that underscores the importance of minimizing hearing loss or excessive environmental noise for healthy infant brain development.”
According to pediatric audiology studies and U.S. census data, approximately 12% of children (or 2.6 million children in the United States) will experience at least one bout of otitis media severe
