[aeternum]

If it were electric fields, wouldn't we also expect the extreme EM fields generated by MRI machines, or even strong permanent magnets held near someone's skull to have some effect on memory?

A nearby lightning strike or overhead power line should also have some effect.

It would be quite amazing if the body were able to neutralize/counter such strong external electric fields.

[sleightofmind]

Good observation. I would not be surprised if the answer to your question is, Yes. An MRI does have some effect on currently active memories and thought. It seems to a non-scientist like me that it would be difficult to use the usual tools to measure this inside an MRI tube, so maybe a hard question to answer for even the experts in measuring such things.

Plenty of folks who do not consider themselves claustrophobic just completely fritz out inside an MRI tube. Could their usual ability to reason about and maintain composure be reduced by just such interference?