Fair hearing

Amy Berntson (right) is a sensory expert.

Dr Berntson, 30, has always been curious about how what we see, hear, touch and taste is processed in the brain.

“The question of how you get information from the environment into the brain has always interested me,” Dr Berntson says. “Evolutionarily our sensory systems have been tuned and pruned to do this complex job really, really fast.”

Raised in the United States, Dr Berntson completed her undergraduate degree at the University of Minnesota. Torn between Graduate School and Medical School, she decided to take a year off and do research, ending up in a German laboratory with two Australians who “I really enjoyed working with”.

Twelve months later, she followed the lead of these two Aussies, Rowland Taylor and Catherine Morgans (now both working in Portland, Oregon), to the John Curtin School of Medical Research at ANU to undertake her PhD.

This focused on tiny cells in the retina, known as photoreceptors, which transduce light intensity into electrical signals that then go to higher retina cells and through the optical nerve to the brain.

“Photoreceptors are the first stage in our complex visual system and I was looking into the limits of that initial process,” Dr Berntson said.

Although she enjoyed this research, investigating the sensory process in the brain is where her real interest lay. She came across an opportunity to work on the auditory system, based in the brain stem, in the Synapse and Hearing Laboratory led by Professor Bruce Walmsley at the John Curtin School of Medical Research.

Her current research focuses on a mutation in a gene in mouse cochlear hair cells known as dn/dn. This mutation also occurs in humans, and those born with this mutated gene are congenitally deaf — it essentially means the cochlear does not register sound and electrical impulses never reach the brain.

The way in which each of our senses receives and feeds information to the brain is essentially the same — a communication line of electrical impulses, each one triggering the next until our brain has interpreted the information.

“We’re trying to understand if someone is deaf from birth and they never hear any sound, what happens to the auditory centres in the brain stem?

“The neurons on the brain side of the cochlear still function, but they’re just sitting there waiting — waiting for something, any sound, to get through.

“We’re pretty sure this part of the brain in a deaf person does not get used for other brain processes. So what is their role in a person who is deaf?

“And if sound does eventually get through to a brain that has never ‘heard’ before, say through a cochlear implant, how is the brain going to process that sound information? Is it going to be different to one which has been ‘hearing’ sound since birth?”

The dn/dn mutation, which has only recently been cloned in humans, causes the degeneration of the inner hairs of the cochlear, which is the hub of sound in a person who can hear. The mutation causes total deafness.

“A cochlear implant basically turns sound vibration into an electrical signal in someone who is deaf,” Dr Berntson says. “The implant winds through the cochlear and directly stimulates the spinal ganglion cells [the next receptors in the auditory process]. This totally bypasses dead or dying hair cells.”

Her work means she travels often, both to other laboratories in Australia and around the world and to large neuroscience conferences.

But she is always happy to come back to her adopted home, Canberra, because it is suited to her interests outside work — mountain biking, rollerblading, rock climbing, swimming and having a garden full of healthy tomato and pumpkin vines.

“I love it here [in Canberra],” Dr Berntson says.

“I grew up in a big city and it was centred around busyness and driving everywhere, so Canberra is really great.”

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