BRAIN activity that is 鈥渟crambled鈥� in deaf cats develops normally if they are fitted with a cochlear implant shortly after birth. The finding may explain how deaf children given implants as babies can learn to speak almost as well as hearing children.
In hearing animals, sound vibrates hair cells in the inner ear, triggering neurons to send impulses to the brain. In deaf animals, these hair cells are often defective; cochlear implants compensate by stimulating neurons directly.
To see how this artificial stimulation affects the brain, Rob Shephard at the in Melbourne, Australia, and colleagues recorded electrical activity in the cortex of 17 8-month-old cats that were deaf from birth. As they monitored the cats鈥� brains, they activated each cat鈥檚 cochlear implant.
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Ten of the cats had received the implant relatively recently and their electrical activity was 鈥渃ompletely scrambled鈥�, indicating that they did not perceive sound coherently: normal cortex activity is key to perceiving sound and, in humans, to developing speech.
In the seven cats that received implants at 8 weeks old, however, activity was similar to that in hearing cats (The Journal of Comparative Neurology, ).
Some deaf people say it is unethical to operate on deaf babies, who would otherwise learn sign language. Neurologist Jim Pickles at the University of Queensland, Australia, says the latest work 鈥渋ncreases the weight of evidence to implant children early鈥�.
