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To add to ericjang's comments elsewhere in this thread, here are my thoughts on the two most popular BCI (although I'm used to seeing BMI -- brain-machine inter

To add to ericjang's comments elsewhere in this thread, here are my thoughts on the two most popular BCI (although I'm used to seeing BMI -- brain-machine interface) technologies: * Optogenetics advantages: don't need to insert things into tissue. Disadvantages: requires genetic engineering that is not approved for human use. Difficulty reaching deep brain targets. To image many neurons, might need to pump lots of light into an area, causing heat and cell death. Bulky. * Microelectrode arrays (https://en.wikipedia.org/wiki/Multielectrode_array https://en.wikipedia.org/wiki/Multielectrode_array) like the Utah or Michigan array advantages: direct electrical recordings, relatively compact. Disadvantages: low density, invasiveness. It is worth noting that most behavioral studies are done with MEAs are due to their convenience/form factor. It is also important to note that these two technologies measure different things: an MEA can record extracellular voltages, so it's a relatively direct measurement of neural activity, compared to optogenetics, which relies on ion channels fluorescing, which is not exactly what most people really want to measure. A word about invasiveness: when you insert large (>1um) things into tissue, you elicit a foreign body response, starting with inflammation and ending with scar tissue or gliosis. The issue with invasive probes like MEAs is that even if you manage to avoid major blood vessels and you control bleeding and inflammation, ultimately scar tissue forms around your probes. Scar tissue is a much worse electrical interface than plain tissue, and thus the effectiveness of your BCI/BMI implant diminishes. Disclosure: I run a company (Paradromics, www.paradromics.com) developing next-generation microwire technology for brain-machine interfaces. Also, my strength is in software so while the gist of what I'm saying is probably mostly correct, I can't give details as well as others can.

djoshea 10y ago
Just to add clarification points, the term optogenetics is generally supposed to refer to any gene transfection that involves optical access, but in practice there are two separate categories: * optogenetic stimulation: using light-activated ion channels to modulate neural activity * optical imaging: using genetically targeted fluorescent proteins (mainly GCaMP) to observe the activity of neurons This article is more the second kind, and the novel aspect is that this technology couples dopamine release to calcium rises, enabling imaging of the calcium signal to be used as a proxy for the neurotransmitter's release. It's more likely to be quite useful for investigating specific scientific questions about neurotransmitter signaling than a general purpose readout for BMI. Multielectrode arrays pick up spikes or action potentials from individual neurons directly, so you get high temporal resolution but from a sparse sample of cells. This sample turns out to be enough to do a lot of interesting things, such as controlling a mouse cursor or a robotic arm. This is already in clinical trials at a few sites, including (my lab at) Stanford. Imaging approaches are really powerful, but the signals are often slower. This has to do with the kinetics of the proteins themselves and the signal that is being detected (calcium is slower than voltage transients). But you get to see the activity of lots of neurons. There are voltage sensitive channels that you can image, although the signal to noise ratio isn't nearly as high as yet. It's not immediately clear how this could be used for a BMI in humans, mainly because you would absolutely need optical access to the brain to image, so you'd either be opening up a window or implanting some kind of imaging sensor. The less invasive approaches you were hinting at are mostly in the first category (stimulation), where for longer wavelengths of light you wouldn't need something as invasive.

djoshea 10y ago

Just to add clarification points, the term optogenetics is generally supposed to refer to any gene transfection that involves optical access, but in practice there are two separate categories: * optogenetic stimulation: using light-activated ion channels to modulate neural activity * optical imaging: using genetically targeted fluorescent proteins (mainly GCaMP) to observe the activity of neurons This article is more the second kind, and the novel aspect is that this technology couples dopamine release to calcium rises, enabling imaging of the calcium signal to be used as a proxy for the neurotransmitter's release. It's more likely to be quite useful for investigating specific scientific questions about neurotransmitter signaling than a general purpose readout for BMI. Multielectrode arrays pick up spikes or action potentials from individual neurons directly, so you get high temporal resolution but from a sparse sample of cells. This sample turns out to be enough to do a lot of interesting things, such as controlling a mouse cursor or a robotic arm. This is already in clinical trials at a few sites, including (my lab at) Stanford. Imaging approaches are really powerful, but the signals are often slower. This has to do with the kinetics of the proteins themselves and the signal that is being detected (calcium is slower than voltage transients). But you get to see the activity of lots of neurons. There are voltage sensitive channels that you can image, although the signal to noise ratio isn't nearly as high as yet. It's not immediately clear how this could be used for a BMI in humans, mainly because you would absolutely need optical access to the brain to image, so you'd either be opening up a window or implanting some kind of imaging sensor. The less invasive approaches you were hinting at are mostly in the first category (stimulation), where for longer wavelengths of light you wouldn't need something as invasive.