Place cells and addictive drugs

BilZ0r BilZ0r at TAKETHISOUThotmail.com
Wed Jun 16 20:33:21 EST 2004

gmsizemore2 at yahoo.com (Glen M. Sizemore) wrote in
news:6e2f1d09.0406161516.2f7f0435 at posting.google.com: 

> B: My idea basically stemed from the fact that people always look at 
> synaptic placsticity in the VTA or the Nucleus Accumbens when they are
> interested in drugs of abuse..
> GS: Do they look for "plasticity?" People, no doubt look at the NAcc
> after exposure to self-administered drugs (or drugs administered
> response-independently), but you almost seem to be implying that it is
> this site where "learning takes place." I think that the role of the
> NAcc is thought to be more of the place where "reinforcement signals"
> are generated. Certainly, though, changes in the NAcc after extended
> exposure to the drug might be thought to reflect the change from
> "recreational use" to "addiction."

No, they really do. Looks at TIPS, vol 26 No 4. I quote "Other recent 
studies have focused on influences by drugs of abuse on synaptic function 
and/or plasticity in the VTA".

> B:  I don't really know why, I wouldn't have 
> thought palsticity there would have explained addiction very well. I 
> always thought that plasticity in the cortex would have far more 
> interesting, i.e. when the reward coincides with a stimuli, then the 
> cortical cells which code/interpret/are activated by that stimuli will
> strengthen there synapses with other downstream neurons, increases the
> attentional weighting of the stimuli. But it would be very hard to
> find a
> neuron which is strongly activated by a particular stimuli (I assume).
> So
> I thought, place cells seem easy enough to find...
> GS: Perhaps the NAcc, and other parts of the basal ganglia and VTA
> etc., produce a diffuse release of neurotransmitter into the PFC,
> association cortices etc., and this produces LTP in the synapses
> between sensory related neurons and motor related neurons. Here, the
> "plasticity" could be "in the cortex," in the sense that that it is
> here that a crucial step is occurring, and changes in NAcc function
> (another kind of plasticity) would drive the "cortex system." I'm not
> really advocating this, I'm just pointing out the ambiguity of your
> question.

Well thats exactly how I would have expected people would have thought it 
would happen, an increase in cortical synaptic strength.
> GS: Fortunately or unfortunately, if you can drive a 20-electrode
> gizmo into a rat's head and find orderly relations between behavior
> and physiology, you can pretty much make up any silly story you want
> to, and it'll be called "science."

But of course, I've realised the flaw in my proposed experiment, 
hippocampal place cells (at least in theory) represent current positions, 
not the goal. What I would want to do, is record from prefrontal cortex 
(or perhaps supplementary motor cortex) cells which represent goals. I've 
read a couple papers about them (goal cells), one done in humans, doing 
the old taxi driver game, but there doesn't seem to be such a reliable 
way of recording them. Still... it was a nice idea

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