British researchers say they have taken a huge step forward in treating deafness after stem cells were used to restore hearing in animals for the first time.

Hearing partially improved when nerves in the ear, which pass sounds into the brain, were rebuilt in gerbils – a UK study in the journal Nature reports.

Getting the same improvement in people would be a shift from being unable to hear traffic to hearing a conversation.

However, treating humans is still a distant prospect.

British researchers say they have taken a huge step forward in treating deafness after stem cells were used to restore hearing in animals for the first time

If you want to listen to the radio or have a chat with a friend your ear has to convert sound waves in the air into electrical signals which the brain will understand.

This happens deep inside the inner ear where vibrations move tiny hairs and this movement creates an electrical signal.

However, in about one in 10 people with profound hearing loss, nerve cells which should pick up the signal are damaged. It is like dropping the baton after the first leg of a relay race.

The aim of researchers at the University of Sheffield was to replace those baton-dropping nerve cells, called spiral ganglion neurons, with new ones.

They used stem cells from a human embryo, which are capable of becoming any other type of cell in the human body from nerve to skin, muscle to kidney.

A chemical soup was added to the stem cells that converted them into cells similar to the spiral ganglion neurons. These were then delicately injected into the inner ears of 18 deaf gerbils.

Over 10 weeks the gerbils’ hearing improved. On average 45% of their hearing range was restored by the end of the study.

Dr. Marcelo Rivolta said: “It would mean going from being so deaf that you wouldn’t be able to hear a lorry or truck in the street to the point where you would be able to hear a conversation.

“It is not a complete cure, they will not be able to hear a whisper, but they would certainly be able to maintain a conversation in a room.”

About a third of the gerbils responded really well to treatment with some regaining up to 90% of their hearing, while just under a third barely responded at all.

Gerbils were used as they are able to hear a similar range of sounds to people, unlike mice which hear higher-pitched sounds.

The researchers detected the improvement in hearing by measuring brainwaves. The gerbils were also tested for only 10 weeks. If this became a treatment in humans then the effect would need to be shown over a much longer term.

There are also questions around the safety and ethics of stem cell treatments which would need to be addressed.