From: gts (gts@optexinc.com)
Date: Wed Aug 28 2002 - 16:32:16 MDT
Rafal,
I had promised a detailed reply to your message in which you reference
the work of Pat Levitt. However after perusing the abstracts on his
website and searching for more articles in the Medline database by him
and others I can find nothing that would contradict anything I've
written here. If I've missed something I'm sure you will show me. :)
> The Knutson article you quote is at variance with a number of
> other publications in falling to find cortical activation
> during reward generation...
Perhaps you've misunderstood me. I have never doubted that certain types
of reward involve cortical activation. For example I have little doubt
that cortical activation is integral to the rewarding feeling that comes
from understanding a complex problem. However the question before us is
"At what location in the brain does the actual experience of reward
arise?" I find it implausible that the experience itself arises from
activity in the cortex.
I think such cortical activation is merely one of many possible triggers
for the pleasurable experience of reward, all of which culminate in
dopaminergic activity in the mesolimbic system.
> ...I say there are many subtle variations of pleasure, almost
> certainly modulated by non-limbic structures.
I agree.
> To put it crudely, the NAc
> doesn't feel happy, the cortex (with NAc's help) does.
Here I disagree. I would say that the NAC feels happy when it is flooded
with dopamine. There are indeed subtle variations in happiness or reward
but these variations are due to the variations in the neurological
pathways all of which lead ultimately to the release of dopamine in the
mesolimbic system.
Consider nicotine as a proxy for any kind of reward stimulus. Studies
show that the rewarding experience that smokers feel when smoking a
cigarette is mediated by dopaminergic activity in the NAC. Addicted
individuals become dependant on that dopamine fix. The drug bupropion
(Wellbutrin, Zyban) is effective for the treatment of nicotine addiction
because it blocks re-uptake of dopamine in the NAC, thus reducing
nicotine cravings.
It seems that all rewarding experiences are activated in the same
manner. As I indicated in a previous post, in men the mere sight of an
attractive woman will flood the NAC with dopamine whereas the sight of a
man or unattractive woman will not.
(Curiously, in women this reward experience in the NAC is triggered by
attractive women as well as by attractive men. This explains why they
put photographs of beautiful women on the cover of Cosmopolitan
magazine. :-)
-gts
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