ultimate goal is to develop technology that they — and many others like them — can take home and use day-to-day to restore the abilities they have lost .
This conversation has been edited for length and clarity .
How do you find out which movements someone with paralysis would like to make ?
We implant a small 4-by-4- millimeter microelectrode array into the brain ’ s motor cortex , in a region that we know directs the movements of the arm . This array consists
of 100 hair-thin silicon needles , each of which picks up the electrical activity of one or two neurons . Those signals are then transmitted through a wire to a computer that we can use to convert the brain activity into instructions to control a machine , or even the person ’ s own arm . We are assuming that the relevant variable here — the language we should try to interpret — is the rate at which neurons discharge , or “ fire .”
Let me explain this using the example of moving a cursor on the screen . We first generate a movie of a cursor moving : say , left and right . We show this to the person and ask them to imagine they are moving a mouse that controls that cursor , and we record the activity of the neurons in their motor cortex while they do so . For example , it might be that every time you think “ left ,” a certain neuron will fire five times — pop pop pop pop pop — and that if you think “ right ,” it will fire ten times . We can use such information to map activity to intention , telling the computer to move the cursor left when the neuron fires five times , and right when it fires ten times .
To record brain activity , scientists implant a 4x4-millimeter microelectrode array ( not drawn to scale here ) into the motor cortex . This array consists of 100 hair-thin silicon needles , each of which picks up the electrical activity of one or two neurons . Those signals are then transmitted by wire , through a “ pedestal ” that crosses the skull and skin , to a computer that decodes them to control computers , prosthetic limbs or real limbs .
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