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Comment by toomuchtodo | Hacker News Reader

Is there anyway to get this signal non invasively (magnetic field detection or photonically)? Or are implanted electrodes table stakes for a neural interface?

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Not really, that we know of. To appreciate the complexity you could read this post[0] from Wait But Why? Your brain has approximately 40,000 neurons in the space of a cubic millimeter. Each saying something completely different. It’s incomprehensible noise unless you start dividing it up like Neuralink has. They get a few thousand probes in the size of a penny, which is a far greater level of resolution than you could probably ever expect from a wireless solution.

[0] https://waitbutwhy.com/2017/04/neuralink.html

Do you think something like fMRI would have enough resolution? Can’t pick up activity directly of course, but perhaps by picking up fluid flow differentials?

As mentioned by a sibling comment, fMRI have a sufficient spatial resolution (i.e. you can watch the activity of a few number of neuron at a time instead of grouping them by batch of hhundreds of them), but the temporal resolution is low (order of magnitude is seconds; a single action potential is 5ms).

Here's a graph that summarize the temporal/spatial tradeoff of the different BMI tech: https://www.researchgate.net/figure/The-various-neural-recor...

Noninvasive signal modality directly from the cortex are certainly possible (e.g. Ultrasound, fNIR). But they lack the spatial and temporal resolution of implanted electrodes. Intracortical brain signals are the most well understood and mature in terms of instrumentation as well. So in the short term, implanted electrodes offer the highest capacity for a BCI.

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