From: Rafal Smigrodzki (rms2g@virginia.edu)
Date: Fri Aug 23 2002 - 12:35:23 MDT
I wrote:
### Can you point me to the research showing that the release of
dopamine in NAc (a physical event) has the experiential correlate of
"pleasure"? I thought we are still far from being able to explain
conscious experiences in mechanistic terms...
--------
gts wrote:
Yes I can point you to such research.
Most current research in this area has come from researchers in the
field of addictionology. This is so because an addiction is essentially
a disease or malfunction of the neurological reward system.
<snip references>
### Thank you for the references you provided. I am roughly familiar with
some of them. Although I was never directly involved in addiction-related
research, I did spend a few years in the lab of Pat Levitt, who aside from
cortical development was also investigating the dopaminergic system and its
abnormal development after in utero cocaine exposure. All these lab meetings
come back to my mind now. Yet, neither the research I remember nor the
references you quote convince me that the limbic system's dopaminergic
activation has directly the experiential correlate of conscious pleasure.
The Knutson article you quote is at variance with a number of other
publications in falling to find cortical activation during reward
generation, which the authors acknowledge and admit their scanning protocol
was likely to miss cortical responses. Studies on rats are not relevant to
our question because we have no data about the rats' subjective experiences,
merely correlations of brain activity and behavior.
Let me reiterate from my previous post - I do not doubt that NAc is very
important in the generation of reward and the subjective experience of
pleasure, maybe even indispensable, in both physiologic and drug-mediated
cases. I do contend, however, that NAc is not *sufficient* to feel pleasure.
As the other fMRI studies show ( Thut G, Schultz W, Roelcke U, Nienhusmeier
M, Missimer J, Maguire
RP, Leenders KL (1997) Activation of the human brain by monetary
reward. NeuroReport 8:1225-1228.,....Elliott R, Friston KJ, Dolan RJ (2000)
Dissociable neural responses in
human reward systems. J Neurosci 20:6159-6165.....O'Doherty J, Kringelbach
ML, Rolls ET, Hornak J, Andrews C (2001)
Abstract reward and punishment representations in the human orbitofrontal
cortex. Nat Neurosci 4:95-102.... and others) cortical areas (some of which
receive inputs from NAc) are active during the experience of pleasure.
Lesion studies on humans concur with these results, showing that certain
cortical lesion abolish or modify these subjective phenomena.
That's why I say there are many subtle variations of pleasure, almost
certainly modulated by non-limbic structures. To put it crudely, the NAc
doesn't feel happy, the cortex (with NAc's help) does.
------
Here is an interesting research abstract in with the authors state that
"The nucleus accumbens is the engine of the reward response."
### To extend this metaphor, the engine is the NAc, but the good(s) are in
the cortical train of thoughts being pulled by it.
BTW, what is your affiliation, if I may ask?
Rafal Smigrodzki, MD-PhD
Clinical Instructor
Department of Neurology
University of Virginia, Charlottesville
email: rms2g@virginia.edu
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