Researchers are exploring a range of options to restore the hair cells of the ear that are lost with age, leading to deafness: "Damage to hair cells in the inner ear due to ageing and overstimulation is a major cause of deafness, affecting 10% of the worldwide population. The cell loss is irreversible because the cells have a limited capacity to regenerate. However, a new study suggests that the ependymal layer of the lateral ventricle of the brain contains stem cells which share characteristics with inner ear hair cells and which have the potential to reproduce. According to the scientists, these cells could potentially be transplanted from a person's brain into their ear, where they would undergo a functional switch to enable them to replace the damaged ones. ... The authors concluded that transplanted cells could alter their functions to work as inner ear hair cells and thus restore hearing. They suggested their findings on the flexible function of certain cells could also be extended to offer treatment for other problems affecting the nervous system."