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Electric Field Effects in the Brain?

Christian Wilms usenet at out-of-phase.de
Sat Apr 19 06:29:16 EST 2003


KP-PC <k.p.collins at worldnet.att.net%remove%> wrote:

> fMRI uses [E]M to [with a lot of help from computers] 'read' neural
> activation dynamics, so it's easy to see that fields do interact with
> the neural tissue. 

This is simply wrong. fMRI uses magnetic fields in the range of several
Tesla - far from any field occuring in the body. This field aligns the
nuclei of certain atoms (the have to be what is called NMR active). This
has no influence on the chemical nature of the involved molecules and
definetly no influence on the neurons. What fMRI 'reads' is the level of
blood oxygenation (the so called BOLD signal), which is believed to be
correlated with the activity of the brain. This is done by monitoring a
change in the magnetic resonance of hemoglobin when it is oxygenated
compared to it's non-oxygenated form.

I'm no MR-physicist so I can't go into more detail here.

Basically magnetic fields can alter processes in the brain -
transcranial magnetic stimulation (TMS) would be a keyword to look up in
this connection. I am not familiar with the details of this method, but
it appears, that strong magnetic fields are applied very focused
directly on the surface of the skull.

Chris 



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