Brainwaves reveal whether young ears can hear

​Babies without language cannot communicate what they hear in a hearing test. However, with new technology, physicians can now measure a baby’s brain activity and find out whether the sound is reaching a baby’s ears.

A weak t-t-t-t-t-t-sound fills the room for a few seconds, but the patient does not seem to notice anything. Even if she did, she – the almost one-year-old Agnes – would not be able to answer meaningfully whether she had heard the sound.

"The very problem of examining the hearing of very young children is that it's not possible to have a conversation with them on a sound, whether or not to turn the sound up a bit or slightly down. Obviously, a baby cannot answer such questions," explained Jesper Borchorst Yde, a consultant at the Department of Otorhinolaryngology, Head and Neck Surgery & Audiology at Rigshospitalet.


The problem is that the earlier you can help a hearing-impaired patient, the better the prospects for the patient. In short, the brain needs to hear as early and as well as possible in order to develop the auditory sense.

“Therefore, whether a patient needs a hearing aid, what kind and how to adjust it does matter. It’s important to know whether the individual patient is moderately hearing impaired, severely hearing impaired or completely deaf,” said Jesper Borchorst Yde.

Fortunately, while she is quietly playing with her small teething toy, Agnes' brain reveals just what Jesper needs to know. We will explain how later.

One of Rigshospitalet's most expensive rooms

Not only one, but two doors have to be closed from each side when patients are being examined at the department at Gentofte Hospital. A copper web has been installed in the walls and doors, and special shutters can be closed from the inside so that nothing that could possibly disturb the hearing tests can get through.

"It is in fact a very expensive room. It can be used for surgery under anaesthesia, it's been screened for electromagnetic signals, and it's soundproof so that our tests are not disturbed," said Jesper Borchorst Yde, who joked that the department will never be relocated because it is too expensive to build new soundproof rooms.

In order to be able to assess the hearing of young children, physicians have so far been using speech and language therapists who are trained in observing what young children can hear. 

"They observe whether the child is turning her head or changing her facial expression when there is a sound. However, when speech and language therapists adjust a hearing aid on a young child, it can be difficult to assess whether the aid has been correctly adjusted to suit the exact needs of the child. Therefore, there's long been a desire to be able to make exact measurements," said Jesper Borchorst Yde.

Brainwaves reveal if there is any hearing

This desire has now been satisfied. Because in the middle of the room is a new CAEP device. Even though it looks more like a PlayStation, it can improve treatment of hearing-impaired children. Via electrodes on the child's forehead, the small machine can measure signals that reveal whether the child's brain is reacting to a sound. 

"When a tiny sound is played, the brain reacts if the sound is heard, and the machine translates this reaction into a small graph on a computer screen. The graph looks like a small mountain landscape, and on the basis of the graph, we can interpret what and how much the child can hear," said Jesper Borchorst Yde. 

This method requires nothing other than electrodes on the child's forehead and that the child is awake. So even though little Agnes does not do much other than chew on her teething toy, her brain tells us whether or not the little girl can hear. This can help a patient like Agnes receive personalised treatment.

Best possible solution

"We can better monitor how the hearing develops from a very young age and thereby better assess whether the child can settle for a hearing aid instead of surgery to insert an electrode into the inner ear. This new measuring technology enables us to choose the best solutions on a more informed basis," said Jesper Borchorst Yde.

The technology is still in its infancy in Denmark.

"There's no red/green light that shows us immediately exactly what we have to do. The results must be interpreted and monitored over a long period, but they provide a pattern according to which we can adjust the choice of treatment over time," the consultant said.

In this process, it is also important to collect and process data to develop a benchmark and research base with Danish patients.

"As more patients receive this treatment, we'll gain experience and results which, in the long term, can be used to improve treatments even more," said Jesper Borchorst Yde who expects to apply the technology on 50-100 patients a year. 
Fact box: The brain reacts when the ears hear
With CAEP technology (Cortical Auditory Evoked Potential), physicians at Rigshospitalet can measure brain activity and thereby whether the patient can hear sounds.
This will particularly benefit very young children who cannot answer for themselves in an ordinary hearing test.
Tiny sounds are played to the patient, and if the brain registers the sound, it will send out brainwaves that can be read in a graph.
CAEP technology thereby guides physicians to find the best treatment and help for the hearing-impaired and the deaf.
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