Serotonin Depletion Prevents Aversive Learning

jjhotcakes

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If I read this study correctly, the claim is that a tryptophan-depleted diet in humans led to a reduction in serotonin (not surprising) and that using classical conditioning for aversive learning, the serotonin-depleted group didn't find the conditioning so effective. In other words, reducing serotonin reduced the aversive response. Or, put another way, we could speculate that reduced serotonin means reduced stress response.

Anyone get a different read of it?

http://journals.plos.org/plosone/articl ... ne.0042397
 

messtafarian

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I think I read the same thing, although what jumped out at me was the designation "autonomic" -- meaning that the response -- to aversive stimuli-- is the "pre-response" -- getting ready for action; in other words, racing heartbeat, dry mouth, cold sweat, etc. It's interesting because that would create potential for ameliorating things like PTSD -- but also interesting because those autonomic responses also involve adrenalin and cortisol.
 
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jjhotcakes

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messtafarian said:
I think I read the same thing, although what jumped out at me was the designation "autonomic" -- meaning that the response -- to aversive stimuli-- is the "pre-response" -- getting ready for action; in other words, racing heartbeat, dry mouth, cold sweat, etc. It's interesting because that would create potential for ameliorating things like PTSD -- but also interesting because those autonomic responses also involve adrenalin and cortisol.

@messtafarian Regarding PTSD, yes, that was the angle from which I was researching 5-ht that led to the paper. Obviously, it isn't clear from that one paper that lowering serotonin can actually have a positive effect on PTSD symptoms, but there's another study that I came across (don't have the link handy) that showed that tianeptine has been used to successfully reduce PTSD symptoms. And one of the suspected mechanisms of tianeptine is lowering free serotonin in the body.

Hugh Johnson said:
Psychopaths have issues with fear conditioning. It seems to have something to do with serotonin.
If serotonin is the 'stop signal' for the organism, is makes sense. If you have no brakes, you are not going to stop just because doing what you want hurts someone else.

@Hugh Johnson Your statement is an interesting one, and I've been investigating this a bit. I dug around for a clear consensus definition of psychopathy. Apparently there is no longer a psychopathy definition in DSM, instead it is anti-social personality disorder. After some digging around, it turns out that wikipedia has the clearest definition, which certainly fits with everything else I read. From http://en.wikipedia.org/wiki/Psychopathy

Boldness. Low fear including stress-tolerance, toleration of unfamiliarity and danger, and high self-confidence and social assertiveness. The PCL-R measures this relatively poorly and mainly through Facet 1 of Factor 1. Similar to PPI Fearless dominance. May correspond to differences in the amygdala and other neurological systems associated with fear.[1][7]
Disinhibition. Poor impulse control including problems with planning and foresight, lacking affect and urge control, demand for immediate gratification, and poor behavioral restraints. Similar to PCL-R Factor 2 and PPI Impulsive antisociality. May correspond to impairments in frontal lobe systems that are involved in such control.[1][7]
Meanness. Lacking empathy and close attachments with others, disdain of close attachments, use of cruelty to gain empowerment, exploitative tendencies, defiance of authority, and destructive excitement seeking. The PCL-R in general is related to this but in particular some elements in Factor 1. Similar to PPI Coldheartedness but also includes elements of subscales in Impulsive antisociality. Meanness may possibly be caused by either high boldness or high disinhibition combined with an adverse environment. A child with high boldness may respond poorly to punishment but may respond better to rewards and secure attachments which may not be available under adverse conditions. A child with high disinhibition may have increased problems under adverse conditions with meanness developing in response.[1][7]

So yes, "boldness"/low fear is apparently a trait of psychopathy. And yes, it may be associated with low serotonin. But I don't see how "boldness" or low fear is inherently negative. In fact, "stress-tolerance, toleration of unfamiliarity and danger, and high self-confidence and social assertiveness" sounds like the sort of thing that most people would want. It is desirable.

But I'm not sure that low serotonin really is a good explanation for psychopathy more generally. The other two points - disinhibition and meanness - aren't associated with low serotonin. Here's a study that claims that "poor impulse control" (disinhibition) is inversely associated with serotonin. And as for meanness...the classic quality of an LSD experience is the antithesis of meanness. (Peat claims that LSD is anti-serotonergic.)

So I think that it's probably too reductionist to associate psychopathy with low serotonin. I expect it's a lot more complex.

As to whether simply lowering serotonin can produce boldness and reduce fear - that isn't clear either. But the reason I posted this study was that it seemed to be a confirmation of Peat's claims that serotonin is a "stress substance".

Anyway, thanks for the comment because it was interesting to learn more about psychopathy - not exactly a warm and fuzzy sort of thing to learn more about, but interesting all the same.
 

Hugh Johnson

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>In fact, "stress-tolerance, toleration of unfamiliarity and danger, and high self-confidence and social assertiveness" sounds like the sort of thing that most people would want. It is desirable.

In our society psychopath males tend to have a lot of children, as they pursue predatory reproductive strategies. It that desirable? Depends on the perspective. For the woman who ended up as a homeless single mother, not so much. Psychopaths can also be pro-social, society does have a use for people with low empathy and high predatory aggression.

Of course it is complex, but I think it can be one of the aspect that can help explain the condition.
 

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