while observing a tetraplegic study participant who has had a microelectrode array — a device smaller than the head of a push pin covered in scads of scaleddown metal spikes — implanted in his SMG . The array can record the firing of individual neurons and transmit the data through a tangle of wires to a computer to process them .
Bjånes likens the setup of their brain-machine interface to a football game . Imagine that your brain is the football stadium , and each of the neurons is a person in that stadium . The electrodes are the microphones you lower into the stadium to listen in .
“ We hope that we place those near the coach , or maybe an announcer , or near some person in the audience that really knows what ’ s going on ,” he explains . “ And then we ’ re trying to understand what ’ s happening on the field . When we hear a roar of the crowd , is that a touchdown ? Was that a pass play ? Was that the quarterback getting sacked ? We ’ re trying to understand the rules of the game , and the more information we can get , the better our device will be .”
In the brain , the implanted devices sit in the extracellular space between neurons , where they monitor the electrochemical signals that move across synapses every time a neuron fires . If the implant picks up on the relevant neurons , the signals that the electrodes record look like audio files , reflecting a different pattern of peaks and valleys for different actions or intentions .
The Caltech team trained their brain-machine interface to recognize the brain patterns produced when a tetraplegic study participant internally “ spoke ” six words ( battlefield , cowboy , python , spoon , swimming , telephone ) and two pseudowords ( nifzig , bindip ). They found that after only 15
Researchers carried out brain-computer interface experiments with the help of a volunteer with tetraplegia who agreed to have electrodes implanted in their brain . This figure shows readings from neurons in a brain region called the supramarginal gyrus , which is strongly activated during speech . The volunteer was tested with a number of words , as well as some nonsense words . The population of neurons triggering the electrode array behaved similarly to each other between tests ( ITI , or inter-trial interval ), but displayed a lot of variability when the subject was shown words ( CUE ), spoke the words internally ( INTERNAL SPEECH ) or spoke the words out loud ( VOCALIZED SPEECH ). Each colored line indicates a different word . The pattern of variance , as indicated by the ups and downs on the vertical axis , enabled words to be distinguished from each other by the computer software .
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