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The ability to discern pitch and to hear the difference between similar-sounding words relies on specialised cells within the inner ear, which can be damaged.

For the first time, scientists have discovered what controls the cells' development and pattering.

They studied the development of these cells in chickens, which unlike humans, have the capacity to regrow sound-detecting cells after suffering hearing loss.

Scientists have discovered what controls the development and pattering of cells in the inner ear. They studies their development in chickens, which can regenerate damaged cells. A coloured microgram of the hair cells that detect pitch are pictured, with stereocilia (hair-like microscopic protrusions) in blue

A study by the University of Virginia School of Medicine and the National Institute on Deafness and Communication Disorders says that if scientists understand what causes chickens' cells to redevelop they could one day replicate the process in humans to reverse hearing loss.

Jeffrey Corwin of the university said that if both a human and a hen were to be exposed to a sound loud enough to destroy the ability to hear a certain pitch, the outcomes would be very different.

'We would lose the ability to hear that sound for the rest of our lives.

'The bird also would lose the ability, but within 10 days, it would have its cells back – they would hook back up to the nerves and within a few weeks its hearing would be back and almost indistinguishable from before.'

'Eventually therapies [for humans] will come about from this regenerative approach and these new discoveries will be a critical component,' he said.

Pitch detection occurs within the cochlea, which is a small spiral structure within the inner ear.

Inside the cochlea are specialised cells, known as hair cells, which are tuned to different sound pitches based in part on their locations along the cochlea's spiral and the number and the length of their stereocilia, which are hair-like microscopic protrusions that give the cells their name.

Egg-straordinary! Experts believe that if they can understand what causes chickens' cells to redevelop, they could replicate the process in humans, which could potentially reverse hearing loss one day

High-pitched sounds are detected by cells with shorter hair bundles, located closest to where sound enters the ear, while lower-pitched sounds are detected by cells with taller hair bundles located further in. This pattern progresses through the several thousand hair cells that are essential for hearing.

Benjamin Thiede, lead author of the two papers, which are published in Nature Communications, explained: 'When you hear different sounds, not every single hair cell in the cochlea is responding - only the ones that are sensitive to the specific sound frequencies.'

Until now, scientists have not understood what orchestrates the formation of this pattern of individually distinct hair cells. But now they have solved that mystery, demonstrating that two specific molecules - Bmp7 and retinoic acid - guide cells to acquire location-specific attributes.

Bmp7 starts the initial patterning process and retinoic acid regulates how the cells' hair bundles grow to different lengths.

Dr Thiede found evidence that there are different levels of retinoic acid activity along the length of the cochlea, so he tried adding more retinoic acid in cells grown in a lab dish and found that they produced longer hair bundles.

Then he used a drug to block retinoic acid's activity and found that resulted in shorter bundles.

He noted that when chickens regenerate damaged hair cells, the new cells develop with just the right characteristics for cells in those particular locations along the cochlea.

'So the question is, are developmental signals like Bmp7 and retinoic acid involved in re-establishing the pattern of hair cells and restoring hearing to the regenerating cochlea?' he asked.

He believes the creation of signals for reactivating regeneration of the molecules is a 'tantalising' path for developing new treatments for hearing loss.