Here are some thoughts on the viability of Brain Computer Interfaces. I know nothing, and am just doing my usual reality checks and initial exploration of random ideas, so please let me know if I’m making any dumb assumptions.
They seem to prefer devices in the blood vessels, due to the low invasiveness. The two specific form factors mentioned are stents and neural dust. Whatever was chosen would have to fit in the larger blood vessels, or flow freely through all of them. Just for fun, let’s choose the second, much narrower constraint, and play with some numbers.
Wikipedia says white blood cells can be up to 30 μm in diameter. (Also, apparently there are multiple kinds of white blood cells. TIL.) I’d guess that we wouldn’t want our neural dust to be any larger than that if we want to be able to give it to someone and be able to reverse the procedure later without any surgery. The injection should be fine, but if you wanted to filter these things back out of your blood, you’d have to do something like giving blood, but with a magnet or something to filter out the neural dust. So, what could we cram into 30 μm?
Well, my first hit when searching “transistors per square mm” is an article titled “Intel Now Packs 100 Million Transistors in Each Square Millimeter”, so let’s go with that. I realize Elon’s ~10 year time horizon would give us another ~6 Moore’s law doublings, but if they did an entire run of a special chip just for this, then maybe they don’t want to pay top dollar for state of the art equipent, so let’s stick with 100m/mm^2. That’d give us on the order of 10k-100k transistors to work with, if we filled the entire area with transistors and nothing else.
But, looking at most electronics, they are more than just a chip. Arduinos and cellphones and motherboards may be built around a chip, but the chip itself has a relatively small footprint on the larger PCB. So, I’m probably missing something which would be incredibly obvious to someone with more hardware experience. (Is all the other stuff just for interfacing with other components and power supplies? In principle, could most of it be done within the chip, if you were willing to do a dedicated manufacturing run just for that one divice, rather than making more modular and flexible chips which can be encorporate into a range of devices?)
If we assume it’d be powered and transmit data electromagnetically, it’d also need an antenna, and an induction coil. I have a hunch that both of these suffer from issues with the square-cube law, so maybe that’s a bad idea. The neural dust article mentioned that the (mm scale) devices both reported information and received power ultrasonically, so maybe the square-cube law is the reason. (If not, we might also run into the diffraction limit, and not have any wavelengths of light which were short enough to effect antenas that size, but still long enough to penetrate the skull without ionizing atoms.)
I like the idea of ultrasonic stuff because acoustic waves travel through tissue without depositing much energy. So, you get around the absorption problem photons have, and don’t have to literally x-ray anyone’s brain. Also, cranial ultrasounds are already a thing for infants, although they have to switch to transcranial Doppler for adults, because our skulls have hardened. Nearby pieces of neural dust would be monitoring the same neurons, and so would give off their signals at about the same time, boosting the signal but maybe smearing it out a little in time.
So, let’s play with some numbers for piezoelectric devices instead. (I assume that’s what their ultrasonic neural dust must be using, at least. They are switching between electricity and motion somehow, and piezoelectrichttps are the name for the solid state way of doing that. I can’t picture them having tiny speakers with electromagnets on flexible speaker cones. The Wikipedia page on transducers doesn’t mention other options.)
Quartz crystals are already used for timing in electronics, so maybe the semiconductor industry already has the ability to make transducers if they wanted to. (I’d be surprised if they didn’t, since quartz is just ccrystaline silicon dioxide. Maybe they can’t get the atomic lattice into the right orientation consistently, though.) If you couldn’t transmit and receive simultaneously without interfering, you’d need a tiny capacitor to store energy for at least 1 cycle. I don’t know how small quartz crystals could be made, or whether size is even the limiting factor. Maybe sufficiently small piezoelectric can’t even put out strong enough pulses to be detectable on an ultrasound, or require too much power to be safely delivered ultrasonically? I don’t know, but I’d have to play with a bunch of numbers to get a good feel.
I don’t really know where to start, when discussing monitoring neuron firings. Could it be done electromagnetically, since they should make an instantaneous electromagnetic field? Or would the signal be too weak near a blood vessel? Apparently each neuron firing changes the concentration of Na, K, Cl, and Ca in the surrounding blood. Could one of these be monitored? Maybe spectrally, with a tiny LED of the appropriate wavelength, and a photo detector? I think such things are miniturizeable in principle, but I’m not sure we can make them with existing semiconductor manufacturing techniques, so the R&D would be expensive. We probably don’t have anything which emits at the exact wavelength we need for spectroscopy though, and even if we did, I bet the LED would need voltage levels which would be hard to deliver without adding a voltage transformer or whatever the DC equivalent is.
Or, can we dump all the fancy electronics all together? Could we do something as simple as a clay particle (tiny rock) coated with a dispersent or other Surfactant, so that changes in the surrounding chemistry cause the collapse of the double layer), making the clay particles to flocculate together? Would such clumps of clay particles be large enough and have high enough density to show up on an ultrasound or other divice? Obviously this wouldn’t let us force a neuron to fire, but it might be a cheap way of detecting them.
Maybe the electronics could be added later, if modifying surface charge and chemistry is enough to make a neuron fire. Neurotransmitrers affect neuron firings somehow, if I usnderstand correctly, so maybe chain a bunch of neurotransmitters to some neural dust as functional groups on the end of polymer chains, then change surface charge to make the chains scrunch up or fan out?
I only know just enough about any of this to get myself into trouble, so if it doesn’t look like I know what I’m talking about, I probably don’t.
(Sorry to spam comments. I’m separating questions out to keep the discussion tidy.)
I would do it by using genetically modified human cells like macrophages, which sit inside blood vessels and register electric activities of the surrounding. It may send information by dumping its log as a DNA chain back into bloodstream. Downstreams such DNA chains will be sorted and read, but it would create time delays.
This way of converting cells into DNA machines will lead eventually to bionanorobots, which will be able to everything original nanobots were intended to do, including neural dust.
Another option is to deliver genetic vectors with genes into some astrocytes, and create inside them some small transmission element, like fluorescent protein reacting on changes of surrounding electric field.
The best solution would be receptor binding drug, like antidepressant (which is legal to deliver into the brain), which also able to transmit information about where and how it has bounded, maybe helping high resolution non-invasive scans.
Here are some thoughts on the viability of Brain Computer Interfaces. I know nothing, and am just doing my usual reality checks and initial exploration of random ideas, so please let me know if I’m making any dumb assumptions.
They seem to prefer devices in the blood vessels, due to the low invasiveness. The two specific form factors mentioned are stents and neural dust. Whatever was chosen would have to fit in the larger blood vessels, or flow freely through all of them. Just for fun, let’s choose the second, much narrower constraint, and play with some numbers.
Wikipedia says white blood cells can be up to 30 μm in diameter. (Also, apparently there are multiple kinds of white blood cells. TIL.) I’d guess that we wouldn’t want our neural dust to be any larger than that if we want to be able to give it to someone and be able to reverse the procedure later without any surgery. The injection should be fine, but if you wanted to filter these things back out of your blood, you’d have to do something like giving blood, but with a magnet or something to filter out the neural dust. So, what could we cram into 30 μm?
Well, my first hit when searching “transistors per square mm” is an article titled “Intel Now Packs 100 Million Transistors in Each Square Millimeter”, so let’s go with that. I realize Elon’s ~10 year time horizon would give us another ~6 Moore’s law doublings, but if they did an entire run of a special chip just for this, then maybe they don’t want to pay top dollar for state of the art equipent, so let’s stick with 100m/mm^2. That’d give us on the order of 10k-100k transistors to work with, if we filled the entire area with transistors and nothing else.
But, looking at most electronics, they are more than just a chip. Arduinos and cellphones and motherboards may be built around a chip, but the chip itself has a relatively small footprint on the larger PCB. So, I’m probably missing something which would be incredibly obvious to someone with more hardware experience. (Is all the other stuff just for interfacing with other components and power supplies? In principle, could most of it be done within the chip, if you were willing to do a dedicated manufacturing run just for that one divice, rather than making more modular and flexible chips which can be encorporate into a range of devices?)
If we assume it’d be powered and transmit data electromagnetically, it’d also need an antenna, and an induction coil. I have a hunch that both of these suffer from issues with the square-cube law, so maybe that’s a bad idea. The neural dust article mentioned that the (mm scale) devices both reported information and received power ultrasonically, so maybe the square-cube law is the reason. (If not, we might also run into the diffraction limit, and not have any wavelengths of light which were short enough to effect antenas that size, but still long enough to penetrate the skull without ionizing atoms.)
I like the idea of ultrasonic stuff because acoustic waves travel through tissue without depositing much energy. So, you get around the absorption problem photons have, and don’t have to literally x-ray anyone’s brain. Also, cranial ultrasounds are already a thing for infants, although they have to switch to transcranial Doppler for adults, because our skulls have hardened. Nearby pieces of neural dust would be monitoring the same neurons, and so would give off their signals at about the same time, boosting the signal but maybe smearing it out a little in time.
So, let’s play with some numbers for piezoelectric devices instead. (I assume that’s what their ultrasonic neural dust must be using, at least. They are switching between electricity and motion somehow, and piezoelectrichttps are the name for the solid state way of doing that. I can’t picture them having tiny speakers with electromagnets on flexible speaker cones. The Wikipedia page on transducers doesn’t mention other options.)
Quartz crystals are already used for timing in electronics, so maybe the semiconductor industry already has the ability to make transducers if they wanted to. (I’d be surprised if they didn’t, since quartz is just ccrystaline silicon dioxide. Maybe they can’t get the atomic lattice into the right orientation consistently, though.) If you couldn’t transmit and receive simultaneously without interfering, you’d need a tiny capacitor to store energy for at least 1 cycle. I don’t know how small quartz crystals could be made, or whether size is even the limiting factor. Maybe sufficiently small piezoelectric can’t even put out strong enough pulses to be detectable on an ultrasound, or require too much power to be safely delivered ultrasonically? I don’t know, but I’d have to play with a bunch of numbers to get a good feel.
I don’t really know where to start, when discussing monitoring neuron firings. Could it be done electromagnetically, since they should make an instantaneous electromagnetic field? Or would the signal be too weak near a blood vessel? Apparently each neuron firing changes the concentration of Na, K, Cl, and Ca in the surrounding blood. Could one of these be monitored? Maybe spectrally, with a tiny LED of the appropriate wavelength, and a photo detector? I think such things are miniturizeable in principle, but I’m not sure we can make them with existing semiconductor manufacturing techniques, so the R&D would be expensive. We probably don’t have anything which emits at the exact wavelength we need for spectroscopy though, and even if we did, I bet the LED would need voltage levels which would be hard to deliver without adding a voltage transformer or whatever the DC equivalent is.
Or, can we dump all the fancy electronics all together? Could we do something as simple as a clay particle (tiny rock) coated with a dispersent or other Surfactant, so that changes in the surrounding chemistry cause the collapse of the double layer), making the clay particles to flocculate together? Would such clumps of clay particles be large enough and have high enough density to show up on an ultrasound or other divice? Obviously this wouldn’t let us force a neuron to fire, but it might be a cheap way of detecting them.
Maybe the electronics could be added later, if modifying surface charge and chemistry is enough to make a neuron fire. Neurotransmitrers affect neuron firings somehow, if I usnderstand correctly, so maybe chain a bunch of neurotransmitters to some neural dust as functional groups on the end of polymer chains, then change surface charge to make the chains scrunch up or fan out?
I only know just enough about any of this to get myself into trouble, so if it doesn’t look like I know what I’m talking about, I probably don’t.
(Sorry to spam comments. I’m separating questions out to keep the discussion tidy.)
I would do it by using genetically modified human cells like macrophages, which sit inside blood vessels and register electric activities of the surrounding. It may send information by dumping its log as a DNA chain back into bloodstream. Downstreams such DNA chains will be sorted and read, but it would create time delays.
This way of converting cells into DNA machines will lead eventually to bionanorobots, which will be able to everything original nanobots were intended to do, including neural dust.
Another option is to deliver genetic vectors with genes into some astrocytes, and create inside them some small transmission element, like fluorescent protein reacting on changes of surrounding electric field.
The best solution would be receptor binding drug, like antidepressant (which is legal to deliver into the brain), which also able to transmit information about where and how it has bounded, maybe helping high resolution non-invasive scans.