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Malenfant comments on [LINK]Real time mapping of neural activity in a larval zebra fish - Less Wrong
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That's really cool. I looked through their methods and (assuming I understand everything) what they did was they added a gene that codes for a fluorescent indicator that associates with calcium channels. Then they took the larval zebrafish and shot a laser at different points of the brain and measured the fluorescence, which changed when the calcium channel was active. Since calcium movement is part of how neurons fire, this let them image neuron firing. This won't work for humans unless we can somehow get this fluoresence gene into all of our neurons, make a laser that goes through our skulls without hurting us, and scale the whole method up about a billion times. Still: I'm hopeful.
Correct, though the indicator was a calcium ion sensor that looked at ion concentrations rather than directly at channel activity. A few more wrinkles (partially informed by another neuron-tracking talk I attended at the university here that used another optogenetic trick to watch neurons firing):
the time resolution was 0.8 seconds, hundreds of times longer than a single neural spike. As such, it shows the average activity level of each neuron during a fraction of that 0.8 second cycle rather than individual spikes. I have seen similar work which watched spikes propagating along individual neurons, but only by taking thousands of very short exposures of thousands of individual spikes and adding them up to produce an average. The amount of light you would need to directly image individual spikes would be directly toxic from breaking chemical bonds in important molecules.
it can find correlations between activities but not causality, with spikes actually propagating and exciting other cells.
I agree about the coolness factor. It's also a step towards uploading and a clue about how difficult it is.