Do blind peo­ple really have a sharp­ened sense of hear­ing? What is the expla­na­tion? This arti­cle reports the work of Ger­man researchers who looked at blind people’s brains to try to answer these ques­tions. They found out that indeed, blind peo­ple can under­stand speech even if sped up beyond the max­i­mum rate that sighted peo­ple can under­stand. This seemed pos­si­ble because the brain areas devoted to vision in peo­ple with eye sight turned out to be respond­ing to speech in blind people.

10 syl­la­bles per sec­ond [is] the absolute limit of com­pre­hen­sion for sighted peo­ple. Blind peo­ple, how­ever, can com­pre­hend speech sped up to 25 syl­la­bles per second.

brain scan­ner revealed that in blind peo­ple the part of the cere­bral cor­tex that nor­mally responds to vision was respond­ing to speech.…somehow an unsighted person’s brain rewires itself to con­nect audi­tory regions of the brain to the visual cortex.

A per­fect exam­ple of neu­ro­plas­tic­ity! Do you think this hap­pens  1) only in peo­ple who are born blind, or  2) only in peo­ple who lose sight later in life,  or 3)  in both cases?

The answer is 2). Indeed, to be rewired con­nec­tions need to pre­ex­ist. This is not the case in peo­ple who are born blind since their visual cor­tex has never received any visual stim­u­la­tion. It is only in peo­ple who lose sight later in life, that the visual con­nec­tions can be rerouted to process audi­tory information.

How does it work?

The fact is that most of our senses have some inter­act­ing cir­cuitry between them, which is called cross modal­ity. […] These con­nec­tions between visual and audi­tory regions of the brain become strength­ened after los­ing sight.

Also, some regions of cere­bral cor­tex that bor­der visual and audi­tory cor­tices […] expand ter­ri­tory in blind peo­ple to make use of the idle cir­cuitry in visual cortex.

Related post: Brain Plas­tic­ity: How learn­ing changes your brain

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