From: Eugene Leitl (eugene.leitl@lrz.uni-muenchen.de)
Date: Sun Oct 25 1998 - 13:19:50 MST
Dennis Roberts writes:
> As someone who routinely subjects various and sundry people to highly
> focused and intense electromagnetic energies during the course of his day
> to day activities, I have to take exception to this thread. While it is true
I think this thread is about transcranial magnetic stimulation
(essentially, a helmet consisting of a geodetic array of magnetic
coils, occasionally fired with GIANT current pulses. I think this has some
limited potential beyond the purely disruptive, if the coil kernal
geometry is tweaked, as the pulse power, and, most importantly, the
right spatiotemporal pulsing sequence. Who knows, with enough R&D the
device might find recreational uses! ;)
> that given sufficient RF input individuals can
> and do percieve direct stimulation to their nervous system ( visual
> sensations, peripheral nerves firing-muscle twitching), it seems highly
> unlikely that an unmodified brain ( one with no little glass electrodes
> imbedded in strategic areas ) could be stimulated in any sort of meaningful
> way. The best focusing that is achieveable in my admittedly non-universal
Agreed.
> experience is about 1mm. That is quite good enough for some outstanding
> diagnostic images ( yes, I'm talking about Magnetic Resonance Imaging ),
Did you know that with the right pulse sequence MRI can induce current
differentials in relatively small voxels? Way better resolution than transcranial
stimulation.
> that still means that you are stimulating a great many neurons and even that
> much focusing requires the recipient to be in a rapidly changing magnetic
> field of cosmic intensity. For those of you who have not had the (pleasure
> ?) of an MRI brain scan, I'll tell you what it feels like. IT'S LOUD!!! The
> rapid alteration in the field gradients that allow image production
Yes, the gradient coils resonate -- and with time you can really
distinguish the pulse sequences -- even without absolute pitch! ;)
> (focusing) produce sounds that are roughly equivalent to being right in
> front of the speaker at a rock concert. It's certainly not something you
> would be unaware of.
Even worse, if you lie motionless in a monotonous, loud environment
for hours (e.g. experimental fMRI scan), with time you get all kinds
of funky acustical and even optical hallucinations due to sensoric
deprivation.
ciao,
'gene
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