>
> So the EM fields account for the experiences that accompany the brain
processes. A kind of epiphenomena.
>
> So why don't my experiences change when I'm in an MRI?
>
I haven't been through the detail - I hope to verify this in my
simulations to come.... but...
As far as I am aware MRI magnets are DC and the technique uses nuclear
spin alignment and measures re-radiated RF as the spins respond to
incident RF. The RF is very high frequency and wont have any net effect on
the neural processes, which are comparatively large scale and very slow.
Although it might heat up the material a bit and affect things that way.
Depends on power levels.
But the effects of superimposed magnetic fields I think could have
multiple effects. There's a possible effect on (a) action potential
propogation and (b) a possible effect on the field expressions responsible
for the subjective qualities.
(a) My initial feeling is that the static fields won't have any net effect
because the geometries of the field expression are symmetrical, so
propogation may be affected on either side of the axon, but the wave still
travels via the unaffected portions. But it could be more subtle in that
you could, depending on field orientation, effect localised arrestation
which might stop processing...and you'd find you couldn't do something as
well or could do something better than before. If you varied the field
strength over time and localised its affects.... as in TMS you can get
effects like this I think.
(b) Qualia generation... this is a relationship of the fields with space.
To alter them I think you'd have to have a very fast change in a specific
direction, - a magnetic gradient significant over the thickness of the
cortex or less. Not sure how you'd do this.
The effects could be very subtle - cognitive functions altered - learning
better/worse...remembering better worse... short term, long term....
But I'm pretty sure that in large scale static fields the net effect is
'common mode', and the processes are 'differential', so nothing will
happen.
I spent a lot of time in an aluminium potline where the fields stopped my
watch and killed floppy discs. Although computer hard disks were OK.
Electron gun CRTs were affected but LCD screens weren't.
Very complex situation.
>> Did you read the painting metaphor? I can't say it any clearer.
>
> I read it - makes no sense to me.
>
> Brent Meeker
>
Shame.
Cheers
colin
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Received on Sat Dec 16 2006 - 21:12:41 PST