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What is the Brain-Machine Interface
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Deep brain stimulation (DBS) has proven to be a remarkable success for the treatment of many movement disorders. The dramatic video below shows what happens to Andrew “Cyber-AJ” Johnson just seconds after he turns off his Medtronic DBS unit. AJ has Parkinson’s disease and his otherwise debilitating tremors are completely eliminated once the stimulators placed in the subthalamic nucleus (STN) of his brain kick in. The obvious question that neurohackers and transhumanists are asking, though, is: What’s so special about the subthalamic nucleus?
Researchers initially hit upon the STN as a site for stimulation when studying monkeys with artificially induced movement disorders. It was known that the drug, MPTP, caused damage to the substantia nigra, the major dopamine-producing part of the brain. The STN is actually right next door to the substantia nigra, and by virtue of its interconnectedness to the motor areas of the brain was a logical site to explore. The other thing going for the STN was that the excitatory output cells there seemed to be spontaneously active ? pacemakers, as some would have it. Neurons there were reliably hammering out spikes at 80 or 90 hertz, even when the monkeys seemed to be doing nothing at all.
The larger story however, is that there is nothing particularly special about stimulating in the STN for gross tremor relief. Both lesions, which eliminate STN activity, and stimulation, which presumably increases it, seem to have similar effects. Furthermore, putting the electrodes instead in any number of surrounding brain nuclei, or passing fiber tracts, seems to have similar beneficial effects.
As we noted in one of our articles on transcranial magnetic stimulation, when there is something seriously wrong with your brain, the stimulation need not be so precise to have a beneficial effect. For example, if your response to someone extending their hand to greet you is to hemiballastically flap both arms in what best be described as a futile attempt to get airborne, any side effects of powerful STN stimulation may be tolerable. For recreational DBS, or its prescriptionless proxy, tDCS (transcranial direct current stimulation), a slightly more informed position may be desirable.
With brain stimulation, the readily observable motor effects, and the more subtle internal emotional correlates that may accompanying it, are not always easy to extricate from one another. In 1999, two middle-aged men with Tourette’s syndrome had their thalamic nuclei implanted with stimulators to curb their motor tics. Their devices were similar, one had a Medtronic 7425 pulse generator, and the other the 7428. For whatever reason, researchers ended up doing some penile plethysmography on these guys ? strain gauges and all. Apparently one bloke was having man problems and had to turn off his device to complete his conjugal relations, while the other chap apparently had just the opposite problem, a little too much excitement.
Long story short, extrapolating stimulation effects from one brain to another is not always reliable. Medtronic, which currently monopolizes the DBS market, does provide for some customizability of the stimulation programs used, and the choice of electrode sites to be used. However, it remains to be seen how much power the end user will have in selecting the settings. Most devices have a current mode, and a voltage mode, and in addition to adjustable stimulation amplitude, common parameters which can be set include, pulse width, pulse width limits, rate, electrode polarity, ramp-up, and brain hemisphere chosen. That is actually a fair bit of control. We can only hope companies do not seek to patent specific programs or stimulation sequences ? as that perhaps would be the height of brain stimulation absurdity. (See: Do you own your genes, or can Big Pharma patent them?)
One major problem with the existing protocol for DBS of the subthalamic nucleus is that the electrodes are destructively plunged into position from the top of the brain (pictured above). There are better ways to access this area of the brain from the bottom if a little more imagination is used. Other parts of the brain might even be accessible transsphenoidally, or through the nose, as is often used to access the pituitary region in surgery. We are not advocating DBS of the pituitary in attempt to release extra growth hormone for aspiring hoopsters, just noting that paying a little attention to cranial anatomy may be useful. For example, there are various natural sinuses close to the brain which may prove to be valuable real estate as communications relays, or other electronics depots.
SinusIn particular, the frontal sinus and the ethmoidal sinus seem to be regular structures from individual to individual, and may ultimately be co-opted into service, provided hardware does interfere with their natural function. In a fashion-aware society, a premium may for some time be put on the appearance of normalcy, and therefore using every cubic centimeter of natural space may be preferable to having the odd, bulbous, protrusion on the scalp.
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