Oct 2019 Newswise
Deafness in early childhood is known to lead to lasting changes in how sounds are processed in the brain, but new research shows that even mild-to-moderate levels of hearing loss in young children can lead to similar changes. Researchers say that the findings may have implications for how babies are screened for hearing loss and how mild-to-moderate hearing loss in children is managed by healthcare providers.
The structure and function of the auditory system, which processes sounds in the brain, develops throughout childhood in response to exposure to sounds. In profoundly deaf children, the auditory system undergoes a functional reorganisation, repurposing itself to respond more to visual stimuli, for example. However, until now relatively little was known about the effects of mild-to-moderate hearing loss during childhood.
A research team led by Dr Lorna Halliday, now at the MRC Cognition and Brain Sciences Unit, University of Cambridge, used an electroencephalogram (EEG) technique to measure the brain responses of 46 children who had been diagnosed with permanent mild-to-moderate hearing loss while they were listening to sounds. Dividing the children into two groups - younger children (8-12 years) and older children (12-16 years) - the team found that the younger children with hearing loss showed relatively typical brain responses - in other words, similar to those of children with normal hearing. However, the brain responses of older children with hearing loss were smaller than those of their normally hearing peers.
To confirm these findings, the researchers re-tested a subset of the group of younger children from the original study, six years later. In the follow-up study, the researchers confirmed that as the children with hearing loss grew older, their brain responses changed. Responses that were present when the children were younger had either disappeared or grown smaller by the time the children were older. There was no evidence that the children's hearing loss had worsened over this time, suggesting instead that a functional reorganisation was occurring.
"We know that children's brains develop in response to exposure to sounds, so it should not be too surprising that even mild-to-moderate levels of hearing loss can lead to changes in the brain," says Dr Axelle Calcus, lead author of the paper, from PSL University, Paris. "However, this does suggest that we need to identify these problems at an earlier stage than is currently the case."
"Current screening programmes for newborn babies are good at picking up moderate-to-profound levels of hearing loss, but not at detecting mild hearing loss. This means that children with mild hearing impairment might not be detected until later in childhood, if at all," says Dr Lorna Halliday from the University of Cambridge. "Children with hearing problems tend to do less well than their peers in terms of language development and academic performance. Detecting even mild degrees of hearing impairment earlier could lead to earlier intervention that would limit these brain changes, and improve children's chances of developing normal language."
HEARING LOSS STILL A CHALLENGE FOR KIDS Oct 2019 Pursuit
Children born with hearing loss are now routinely diagnosed within weeks of birth – having hearing aids and cochlear implants fitted well before school. So why are they still lagging behind their hearing peers in language? In the last 20 years, we’ve made dramatic advances in the early detection of hearing loss in newborn babies and in providing early access to hearing aids and cochlear implants. For example, since 2012 in Victoria, the median age at which hearing loss is detected in newborns is measured in just weeks; this compared to a median 20 months of age back in 1989. And in 2018, more than 2,800 Australian children were fitted with either a hearing aid or cochlear implant for the first time, many within the first year of life, and the majority prior to starting school.
Given this massive improvement in early detection and intervention it could have been expected that hearing impaired children would have quickly come to enjoy the same language and educational outcomes as their hearing peers. But, this hasn’t happened consistently for all children and we don’t know why. The big improvements in early detection have been driven by the widespread adoption in Australia of universal newborn hearing screening (UNHS), which was first rolled out in New South Wales in 2002 and 2005 in Victoria. This involves playing soft clicks into the baby’s ear while they sleep. Small recording pads on the baby’s head and neck measure the baby’s electrical responses to the sound.
But, while we have seen some improvements in language outcomes for hearing impaired children, according to a recent study, they still have much poorer outcomes compared with their hearing peers. What’s more, the same study showed that for those children with mild hearing loss, there has been no clear improvement in language outcomes. This is a major problem. Globally, up to three in every 1000 babies are born with some level of hearing loss. In Australia around 350 children a year, or the equivalent of one child every day, is diagnosed with a permanent hearing loss.
Systematic reviews of published evidence suggest we have a long way to go with understanding what works best for children with hearing loss. For example, there is no consensus on what intervention works best for developing spoken language in children with hearing loss. The evidence that does exist hasn’t been validated by experimental controls, and is somewhat focused on the outcomes of children with cochlear implants – those children who have the greatest level of hearing loss.
A baby undergoes a hearing test. Picture: Courtesy of the Victorian Infant Hearing Screening Program
Yet, the majority of hearing-impaired children have a milder degree of hearing loss. It may be then that a ‘one size fits all’ approach may not be the most effective way to assist impacted children achieve language outcomes that match their cognitive potential. Indeed, babies and young children identified with mild hearing loss have, until recently, gone undetected. Historically, prior to the introduction of UNHS, these children didn’t receive a diagnosis until much later, usually when problems arose at school. Now that we are identifying them early, we need more research to identify the best ways to help these children. Is it possible that children with mild hearing loss don’t benefit from hearing aids to the same extent as children with more severe hearing impairment?
Do we have an issue with terminology, where parents consider a ‘mild’ hearing loss as something not to be concerned about and, therefore, they may feel early intervention is less important? Is the impact of hearing aids cumulative, where each and every day the child consistently wears their device it adds to a ‘bank of benefit’ for their language development overall – helping them to reach their potential through this cumulative auditory experience?
There may be no “one-size fits all” approach to helping hearing impaired children learn language
And how do we help families persist with consistent device use, if this really helps, when their child seems to respond normally even when not wearing their hearing aids? These are just some of the many unresolved research questions around hearing loss in newborns. To help find answers to these questions, we need large observational studies representative of children with all degrees of hearing loss followed over long periods of time to capture their outcomes, as well as rigorous population-based intervention trials.
To date, these are lacking internationally. This is why the Victorian Childhood Hearing Impairment Longitudinal Databank (VicCHILD) is so important. It is a unique statewide databank of hearing-impaired children designed to help researchers all over the world understand why some children with hearing loss adapt and thrive, while others struggle. The databank has been developed over the past eight years, and has been built on a body of work going back 25 years by researchers and clinicians from the Royal Children’s Hospital, the Murdoch Children’s Research Institute and the University of Melbourne. More than 800 children and their families have now provided baseline hearing, clinical, sociodemographic, health service and quality of life data along with saliva samples – with most families consenting to have other personal data linked into the database and agreeing to be re-contacted for future research projects. The children in VicCHILD are assessed at key developmental timepoints – around two, five and 10 years of age – for their language, developmental and quality of life outcomes.