The visual cortex, the part of the brain that receives information from the eyes, has been known to respond to sound or touch in people who are blind. Researchers have now shown it may be unwittingly repurposed to process movement.
鈥淎fter the loss of vision, the visual cortex loses its primary purpose,鈥� says at the National Institute of Information and Communications Technology in Japan. 鈥淚t鈥檚 a waste of brain resources鈥� so it鈥檚 an essential characteristic of our brain that it allows the visual cortex to be reorganised for different purposes.鈥�
Ikegami and his colleagues set out to uncover if this reorganisation also involves motor control. This is ordinarily regulated by the motor cortex in the brain鈥檚 frontal lobe.
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The team studied 24 people, with an average age of 27, half of whom were blind. All the participants were blindfolded while having transcranial magnetic stimulation applied to the part of the brain where the visual cortex is located.
TMS is a non-invasive form of stimulation that uses changing magnetic fields to send an electric current to the brain, altering its activity.
The participants were asked to move their feet up and down while TMS was applied. Being blindfolded ensured that any difference in the participants鈥� movement wasn鈥檛 due to some of them being able to see their feet.
Applying TMS was found to slightly disrupt the movement of those participants who were blind, but not those with sight. This suggests the visual cortex had been reorganised in the people who were blind, with this part of the brain now being involved in foot movements, says Ikegami. The team didn鈥檛 test how other body movements may be affected by TMS.
鈥淥ur data only suggests the visual cortex may be involved in motor control,鈥� he says. 鈥淚t cannot say how much it is involved.鈥�
But at the University of Oxford is sceptical. The movement disruption may have been caused by the interruption of the brain鈥檚 rhythm control systems, which could have been partially taken over by the visual cortex among the people who were blind, she says.
Previous studies suggest the visual cortex in people who are blind can be reorganised to become activated by language and hearing, says Bridge, 鈥渂oth of which require rhythm and timing information. In this case, rather than motor function, the changes could be due to disruption of timing information in the 鈥榲isual鈥� cortex. We鈥檝e never seen the visual cortex being involved in motor activity in the literature before.鈥�
Ikegami agrees this may be true, with the mechanism behind the results being unclear. If the visual cortex is involved in the motor activity of people who are blind, it is unlikely to have anything to do with generating movement, he says.
鈥淚 believe the visual cortex does not contribute to motor command generation because if this was true we should observe immediately the muscle stopping or affected by transcranial stimulation,鈥� says Ikegami.
It is unclear if this research could one day help people who are blind. But studies like this may help to shed light on how elite athletes can become so skilled with their hand and feet movements that they rely less on visual cues, says Ikegami.
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