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Deep-brain stimulation is different than cortical microstimulation. DBS is injected into the basal ganglia and excites an area of the brain that's effectively
by frisco 16y ago
Deep-brain stimulation is different than cortical microstimulation. DBS is injected into the basal ganglia and excites an area of the brain that's effectively atrophied. This can be done relatively safely for things like Parkinsons, even though it's definitely not your first choice of treatment. It's still somewhat cooking the brain, however; in the cases where DBS is used that just doesn't outweigh the benefits. Cortical stimulation into primary sensory cortex is a totally different animal, and tends to cause seizures much more frequently. The brain is kind of wired to seize, when you look at it, and it's amazing it doesn't more often. Also, you can't map receptive fields -- which specific areas of cortex correspond to what sensation in what part of the body -- if your patient is an amputee, and there's no "master map" that's precise enough since it varies between individuals widely. Further, DBS is just designed to grossly "drive" an area of the brain; in ICMS you'd want to precisely excite a few cells to create a sensation. ICMS in practice just floods its surroundings with current in a rather blunt way. Optogenetics are a solution but have their own problems (i.e., requires genetic transfection) that make them unacceptable for use in humans today.
This part is easy, isn't it? People integrate tools into their body image innately and easily.
Yes -- but as a patient lives with a prosthetic full time, as opposed for a few hours at a time like in most monkey studies, the brain will adapt to the prosthetic and the neural representations shift. You need to be able to deal with this and understand what that learning looks like, which we can sort of do right now, but no one's really done a long-term-continuously-living-with-a-prosthetic study. You generally don't try to solve complete unknowns like that for the first time in humans. Humans would be a poor platform, anyway, since you can't observe and record from them 24/7 in a controlled environment.
- joeyo 16y ago> Also, you can't map receptive fields -- which specific > areas of cortex correspond to what sensation in what part > of the body -- if your patient is an amputee, and there's > no "master map" that's precise enough since it varies > between individuals widely. This is a very good point but I don't think it's an insurmountable problem. After amputation or deafferentation the "unused" parts of the cortical map get taken over by adjacent representation areas. However, after hand transplantation cortex recovers some of it's normal organization[1]. So it's at least possible that cortical stimulation could lead to the same result. 1. Frey et al. Chronically deafferented sensory cortex recovers a grossly typical organization after allogenic hand transplantation. Curr. Biol. (2008) vol. 18 (19) pp. 1530-4
- erikpukinskis 16y agothe brain will adapt to the prosthetic and the neural representations shift. You need to be able to deal with this Why? Sounds like the brain is dealing with it pretty well on its own. If the brain is good at one thing, it's taking note of, and adapting to, useful relationships in the structures it finds itself embedded in (affordances). I think if you can get some kind of probe or grid of probes into an area that has even a vague chance of getting some activation during physical therapy sessions, then there's a pretty good chance the patient will be able to get from there to skilled motor control through practice.