Of course , there are other decisions to be made : What if a neuron fires just three times ? So you need a computer model to decide which numbers are close enough to five . And since neuronal activity is naturally noisy , the more neurons we can measure , the better our prediction will be — with the array we implant , we usually get measurements from 50 to 200 .
For the arm prosthesis , we similarly ask people to imagine making the same movement with their own arm . There were people who thought you would have to build separate models for “ flex and extend your elbow ,” “ move your wrist up and down ,”
and so on . But it turns out this isn ’ t necessary . The brain doesn ’ t think in terms of muscles or joint angles — the translation of intentions into movement happens later .
How do you find the exact spot in the motor cortex at which to implant the array ?
In fact , I don ’ t think the exact location matters that much . There is also no need for us to know exactly what each individual neuron is trying to do , as long as we can dependably predict the intended action from their combined activity . That goes against the standard old theory that there is a separate location for controlling each finger , for example . If that were the case , it would mean that if you put the array in a particular place you ’ d get great thumb control , but nothing else . I ’ ve spent my entire scientific career saying it is not true that doing something only engages a small and specific part of the brain . All our neurons form parts of large , interconnected networks .
Do people get better with experience in using the device ?
Not really . The neurons often
This video describes how brain-machine interfaces can allow people with paralysis to control cursors on computer screens and , even more challenging , move prosthetic devices or their own limbs . You ’ ll see Cathy Hutchinson use a robotic arm to bring a bottle up to her face and sip coffee from a straw — independently , for the first time in almost 15 years .
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