[tbenst]

Neuroscience PhD student here. The skull acts as a low-pass filter. EEG recordings are typically low pass filtered at 70Hz or lower for example. This is why you can’t decode eg speech from a EEG: the neural encoding is at a higher frequency band than can be recorded. Even though the signal is much stronger, digital comms equipment is orders of magnitude higher in frequency and does not penetrate the skull well.

[est31]

What about the radio signal used for MRI imaging, is it blocked by the skull as well? Or is it just strong enough to be able to penetrate the skull?

[tbenst]

fMRIs use a crazy strong magnetic field—typically >= 3 Tesla. The signal that is measured is not electrical but rather the blood oxygen level. Effectively, this is a correlate of the metabolic expenditure of nearby neurons. Wass it is also like a low-pass filter except here it’s more like 0.5 Hz or slower. On the plus, you get much improved spatial resolution

[est31]

MRIs use two magnetic fields, a static one and a dynamic one. And they use a radio signal according to the larmor frequency to excite the spin of the atoms. I was wondering about that radio signal component.