Proceedings of a Workshop on Statistics on Networks (CD-ROM) (2007) / Chapter Skim
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Data and Measurement--Current Developments in a Cortically Controlled Brain-Machine Interface--Nicho Hatsopoulos, University of Chicago
Data and Measurement--Current Developments in a Cortically Controlled Brain-Machine Interface--Nicho Hatsopoulos, University of Chicago
Pages 188-206
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From page 188... ...
Data and Measurement 188
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From page 189... ...
Typical of the motor cortex, it starts firing maybe 200 or 300 milliseconds before the moving begins, and it is believed to be intimately involved in driving the arm, driving the motor neurons in the spinal cord that ultimately activate the muscles and move the arm. This same approach has been used in the sensory domain as well.
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From page 190... ...
We put in multiple sensors, multiple electrodes in a particular area of the brain, the motor cortex, record multiple single neurons, their action potential, and based on the activity on a single trial, tried to predict what the animal was going to do. We don't have the luxury of trial averaging, we just have a snapshot of activity at a certain moment in time and try to predict what the animal is doing.
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From page 191... ...
First, by putting this in a spinal cord injury patient, could we extract human signals from a human cortex? That hadn't been shown before, at least with this particular device.
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From page 192... ...
Figure 4 shows examples of raster plots from three channels while we had the patient imagine opening and closing his hand. You can see all three of these neurons tend to fire when he imagines closing the hand, and then stop firing when he imagines opening the hand.
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From page 193... ...
[A video clip was shown at the workshop.] When the technician asks the patient to think about moving the whole arm either to the left or to the right or relax, the top raster plot displays a big burst of spiking as the patient imagines moving his arm to the left.
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From page 194... ...
Over multiple trials they generate the kind of mess shown in the lower left. To get at the discrete mode of operation we use a much more common task, which is called a center-out task, where basically the monkey reaches from a center target to one of eight targets positioned radically away from the center, and keep repeating, doing the same task over to one target.
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From page 195... ...
For the most part we have implanted in the arm area of the primary motor cortex. Since I moved to Chicago I have been doing these dual array implants, and am now doing triple array implants, but I will be showing you these dual array implants where we have a second array implanted in the pre-motor cortex in the dorsal part of the pre-motor cortex, which is believed to be involved in this early planning or target selection process.
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From page 196... ...
The pre-motor cortex signals will be fed into a discrete decoder to predict which target the animal is going to go to. If the monkey incorrectly predicts, based on his brain activity, which target he is going to go to we then switch to a continuous mode based on signals in the motor cortex.
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From page 197... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensembles." Journal of Neurophysiology 92:11651174.
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From page 198... ...
Figure 10 shows the results from a monkey playing that random walk task; he is jumping around and you can see he is oscillating; he is doing harmonic oscillation. M-1 activity predicts better than pre-motor cortex.
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From page 199... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensemble." Journal of Neurophysiology 92:11651174.
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From page 200... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensembles." Journal of Neurophysiology 92:11651174.
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From page 201... ...
Yet we have shown in real time applications with patients and with our monkeys that it is irrelevant whether or not we were restricting the hand. The fact is the animal and the patient can control the cursor remarkably well so this is the continuous mode.
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From page 202... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensembles." Journal of Neurophysiology 92:11651174.
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From page 203... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensembles." Journal of Neurophysiology 92:11651174.
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From page 204... ...
. "Decoding continuous and discrete motor behavior from motor and premotor cortical ensembles." Journal of Neurophysiology 92:11651174.
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From page 205... ...
They basically have to associate certain global brain signal brain patterns with certain movements or certain targets, and it takes a lot of training to get them to do that. With this device, it is invasive, that is the draw back, but the pro to this approach is we are extracting signals from the motor area, the area that was intentionally used in the normal intact system to control the arm, and this requires no training at all.
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From page 206... ...
Basically in about 10 to 15 percent of cell pairs, we find evidence of synchronization, anywhere from a millisecond to 20 milliseconds. If you plot a cross-correlation histogram, we find some widths that are very narrow, maybe three millisecond widths, and other ranging all the way up to 20 milliseconds.
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