Psychopathy and Vagus Nerve, a possible connection?

[Biomiast]

Hi zlyja,

Great blog you have found there. I think septum is very important for the neurological aspect of the psychopathology. Also I have found another page that summarizes deficiencies found in psychopaths:

1. Disconnected uncinate fasciculus , between the limbic system and the frontal lobes (and see this recent report, this white matter tract feeds right into the reward circuits),

2. Ginormous striatum hugry for dopamine (and see this recent report, psychopaths supersize the dopamine response to amphetamines, indicating hypersensitivity to rewards);

3. Brain midline problem, the cavum septum pellucidum reported above, possibly indicating limited introspective ability.

That about covers it — the unbridled rages with no frontal lobe cooling off (because of the white matter disconnnect), the hunger for power because of the big striatum – and not a hunger for love because that wiring is disconnected, and the lack of compassion, based on the brain midline malformation.

http://neurologicalcorrelates.com/wordpress/2010/09/06/neurological-correlates-is-3-almost-plus-the-trifecta-of-the-psychopaths-brain/

Does anybody know to whom this blog belongs to? His/her writing has a similar flavor to Sott.

So in summary, they have a disconnect between limbic system and frontol lobes which makes them uncontrolled or makes them fixed towards their goal without inhibition, they have a big striatum so they seek dopamine surges, and respond to dopamine much higher. Since dopamine is about anticipation of reward, we can say that this is yet another example of how they are fixed for a certain reward they want, regardless of negative stimuli which they are unable to process. They also have a septum missing along with oxytocin receptors which is associated with bonding and compassion.

When I start to think about it, it feels like this is a machine designed for a specific purpose.

The author of this blog talks a lot about retinoid toxicity as a possible cause of psychopathy.

http://neurologicalcorrelates.com/wordpress/2009/09/04/unified-field-theory-of-psychopath-brain-development-retinoid-toxicity/

[zlyja]

Yep, it's a really great blog. The author is anonymous, but I think he either is a graduate student or has a master's in neuroscience; I'm not sure.

I think that the author is a great source for getting a more down-to-Earth explanation of the biology of psychopathy, but some things that he says I think are unlikely, like how he speculates that a high-fat diet or maternal smoking may contribute to the development of aggression.

For instance, I think his theory about problems with the hedgehog protein during fetal development (http://neurologicalcorrelates.com/wordpress/2009/12/14/manic-monday-your-brain-on-hedgehog/) is very interesting, and I'll try to summarize it. Basically, hedgehog protein needs to bind with cholesterol in order to grow your cells, form myelin, and help the skull and brain develop properly. Then, the author mentions that some forms of oxysterols are needed to activate the Liver X Receptor, which is responsible for lipid homeostasis and signaling the cleanup of dead cells from the body. Oxysterols themselves "cause cells to suicide" and, if LXR and oxysterols are chronically activated, they can both cause "pancreatic b-cell death -- which may be why people get type 2 diabetes". The author speculates that this cycle may be because of too much fat and cholesterol in the diet, but I think it's more likely that free radicals are to blame for the oxidization of cholesterol than due to processing it constantly.

Anyways, this is relevant because oxysterols and LXR promote the growth of the ventral midbrain, which is responsible for dopamine-related reward circuitry. Also, hedgehog protein is responsible for making axons grow in the right direction; a deficiency of this protein in psychopaths could explain frayed white matter, as well as any problems in myelin sheathing. In the author's own words:

Taken together, where hedgehog is key in craniofacial and brain midline gestational development (see the teratogenic papers above), and where the very thing that inhibits hedgehog activity — oxysterol — promotes midbrain neurogenesis, it looks like there’s a serious sequence of events that has to happen gestationally so that the dopamine system functions properly. For instance, with an alcohol spike — which would, apparently, decouple the cholesterol from the hedgehog protein, thereby disabling the hedgehog protein, the ventral midbrain dopaminergic axons could be wired improperly. Combine that with oxysterols being not great for blood vessels, and you have a double whammy in utero: the placental arteries going bad, plus the blood that does get through has ethanol in it — so it decouples the hedgehog from cholesterol once it gets to the fetus. Bad news.

I think that the author is onto something with the alcohol. I think it's also worth considering that alcohol consumption was born from the dawn of agriculture; with all of those grains and fruit, they had to do something to preserve them, and making alcoholic beverages is a pleasurable way of not letting your harvest go to waste. And we all know how the war-prone Egyptians, Romans, Vikings, etc. loved their alcohol. Not to mention that alcohol promotes free radical damage, damaging precious cholesterol and fats. Of course, I think that the SAD without alcohol or a diet too low in cholesterol could have the same effects on a baby.

Unfortunately, I don't see how that has much to do with the vagus nerve.

As far as the retinoic acid (vitamin A) overload theory goes, I think it's compelling, but I don't understand how one could get enough of it to cause a problem. As far as I know, you would have to eat about 400g of beef liver (over 100,000 UI vitamin A) or use way too much Retin-A to have that kind of problem. On a side note, this (http://www.springerlink.com/content/3kj561b0ax7tr0p9/) paper mentions that chicks treated with all-trans-retinoic acid have irregular patterning of the vagus nerve in their hearts, which may or may not be important.

Also, maybe you've seen this by now, but the author also says (http://neurologicalcorrelates.com/wordpress/2011/07/25/psychopath-white-matter-abnormal-mostly-on-the-right-hand-side/) that psychopaths tend to have less white matter on the right lobes of their brains, where the VENs are supposed to be. Quite interesting stuff!

[Biomiast]

We seem to get side-tracked with the topic at hand. zylja, I looked at some of the connections like hedgehog but couldn't find any research done on them. Yet, your reasoning makes sense, it is something to be studied by scientists, but there will be some time before they get to this part. Getting back to low arousal, there is a lengthy quote, I bolded the important parts.

Basically it argues that while low heart rate is associated with psychopathy, in psychopaths, vagus nerve activity is not increased, it is decreased. Since this should be the opposite with the low resting heart rate, authors list other mechanisms that is associated with low resting heart rate and list some of the possible causes for psychopathy. Reduced noradrenergic functioning and Reduced right hemisphere functioning seems to be good candidates since they can be measured analytically and they seem to fit in with the data at hand.

What are the mechanisms whereby low resting heart rate predisposes to antisocial behavior? Low arousal, stimulation seeking, fearlessness, increased vagal tone/vagal passive coping, reduced noradrenergic functioning, and reduced right hemisphere functioning represent several of the possible processes which, either by themselves or in combination, may predispose a child to aggression. Physiological explanations of the heart rate–antisocial relationship consist of arousal theory, vagal tone, norepinephrine, and right hemisphere dysfunction.

Low arousal. The most obvious and simple physiological explanation is that heart rate is a measure of autonomic arousal, and that low physiological arousal in general is a predisposition to antisocial and criminal behavior (Eysenck, 1987; Raine et al., 1990). In support of this relatively simple theory, which also invokes stimulation-seeking (see below), there is growing evidence that other measures of autonomic and central nervous system functioning, including resting EEG (Raine et al., 1990), skin conductance activity (Fowles, 1993; Raine et al., 1990), and cortisol (McBurnett et al., 1991; Susman& Petersen, 1992; van Goozen et al., 1998) are related to antisocial and conduct disordered behavior in children.

On the other hand there appears to be no unitary arousal system, as intercorrelations between these different measures of arousal are low or even nonexistent in the general population (e.g., Raine et al., 1990). However, it is conceivable that an extreme(antisocial) group within this general population does have low arousal on multiple arousal measures. Some evidence does exist for underarousal on at least two separate physiological measures of arousal in antisocial child and adolescent samples (e.g., van Goozen et al., 1998; Raine et al., 1990).

Stimulation seeking theory. Stimulation-seeking theory argues that low arousal represents an unpleasant physiological state; antisocial individuals seek stimulation in order to increase their arousal levels to an optimal or normal level (Eysenck, 1997; Quay, 1965; Raine et al., 1997a). Antisocial behavior is thus viewed as a form of stimulation-seeking, in that committing a burglary, assault, or robbery could be stimulating for some individuals. In support of this theory, El-Sheik, Ballard, and Cummings (1994) found that preschool boys who chose to watch videotapes depicting intense anger had lower heart rates than controls, and also that low resting heart rate was associated with externalizing problems. This indicates some support for the view that low heart rate characterizes both stimulation-seeking and antisocial behavior. Similarly, resting heart rate at age 3 years has been found to characterize stimulation-seeking behavior at 3 years, as well as aggressive behavior at 11 years (Raine et al., 1997a, 1998a).

Fearlessness theory. Fearlessness theory argues that low levels of arousal during mildly stressful psychophysiological test sessions are markers of low levels of fear (Raine, 1993, 1997). For example, particularly fearless individuals such as bomb disposal experts who have been decorated for their bravery have particularly low heart rate levels and reactivity (Cox, Hallam, O’Connor, & Rachman, 1983; O’Connor, Hallam, & Rachman, 1985), as do British paratroopers decorated in the Falklands war(McMillan & Rachman, 1987). Antisocial and violent behavior (e.g., fights and assaults) requires a degree of fearlessness to execute, and lack of fear of socializing punishments in early childhood would contribute to poor fear conditioning and lack of conscience development (Raine, 1993). Fearlessness theory receives support from the fact that low heart rate also provides the underpinning for a fearless or uninhibited temperament in infancy and childhood (Scarpa, Raine, Venables, &Mednick, 1997; Kagan, 1994).

Vagal tone. Another physiological mechanisms to account for the heart rate–antisocial relationship is increased vagal tone. Raine and Venables (1984) first suggested that the low heart rate recorded in antisocial individuals may be a function of increased vagal tone and reflect a passive coping response to mildly stressful situations (i.e., so-called ‘resting states’ prior to some other experimental manipulation). Data since then have not supported this hypothesis, favoring instead increased parasympathetic activity in antisocial individuals. For example, Mezzacappa et al. (1997) found that antisocial 15-yearold boys were characterized by low resting heart rates, but also found evidence for reduced, not increased, vagal functioning. Furthermore, Pine et al. (1996) found reduced, not increased, vagal tone was associated with aggressive behavior in children. If reduced vagal tone does prove a systematic correlate of antisocial behavior, it will indicate that the resting heart rate–antisocial relationship is driven by particularly strong sympathetic underarousal which is powerful enough to overcompensate for the lack of parasympathetic influences (low vagal tone) which would otherwise be expected to increase heart rate in antisocial children.


Reduced noradrenergic functioning. Strong underarousal of the sympathetic nervous system would support a neurochemical explanation of the heart rate–antisocial relationship based on reduced noradrenergic functioning. The monoamine norepinephrine, found in autonomic nervous system neurons and produced in the locus coeruleus, is centrally involved in attention and vigilance and forms one of the four arousal systems in the brainstem. While studies of peripheral measures of norepinephrine in antisocial children have found weak positive or null effects (Berman, Kavoussi, & Coccaro, 1997), a meta-analytic review found a significant negative effect size of .41 between reduced central (cerebrospinal fluid) measures of norepinephrine and increased antisocial behavior (Raine, 1993). Furthermore, Rogeness et al. (1990a, b) found both reduced heart rate and reduced noradrenaline in conduct disordered children.


Reduced right hemisphere functioning. Poor right hemisphere functioning could underlie the low heart rate–antisocial relationship. The right hemisphere is dominant for the control of autonomic functions, including heart rate (Lane & Jennings, 1995) and both lesion and intracarotid amobarbital studies confirm that reduced heart rate is associated with decreased right hemisphere functioning (Zamrini et al., 1990; Yokoyama, Jennings, Ackles, Hood, & Boller, 1987). In turn, although left hemisphere dysfunction has frequently been implicated in violence and crime (Raine, 1993), poor right hemisphere functioning has also been found in antisocial and violent populations as measured by functional magnetic resonance imaging (fMRI – Raine et al., 2001a), computerized tomography (CT – Hucker et al., 1988), neuropsychological tests (Day & Wong, 1996), spatial IQ measures (Raine, Yaralian, Reynolds, Venables, & Mednick, in press), EEG deficits (Evans & Park, 1997), and event-related potentials (ERPs – Drake, Pakalnis, Brown, & Hietter, 1988). Poor right hemisphere functioning (particularly the anterior regions) has been associated with deficits in the withdrawal system, a system that promotes retreat from aversive and dangerous situations (Davidson, Eckman, Saron, Senulis, & Friesen, 1990; Davidson, 1998). Furthermore, patients with right hemisphere lesions, compared to  those with left hemisphere lesions, have been shown to have reduced heart rate and skin conductance responses to films depicting negative emotions (e.g., anger) (Zoccolotti, Caltagirone, Benedetti, & Gainotti, 1986). Reduced right hemisphere functioning and a consequent weaker withdrawal system could make children less averse to dangerous, risky situations that increase the probability of antisocial behavior.

Annotation:The role of prefrontal deficits, low autonomic arousal, and early health factors in the development of antisocial and
aggressive behavior in children, Adrian Raine Journal of Child Psychology and Psychiatry 43:4 (2002), pp 417–434

http://onlinelibrary.wiley.com/doi/10.1111/1469-7610.00034/full

[zlyja]

Apologies for venturing away from the main idea of the thread, Biomiast. I have the habit of getting interested in new details, and then forgetting completely about what I was searching for in the first place. I'll try to be more considerate of that next time.

Also, geez, I completely misinterpreted what you previously posted near the beginning of the thread, because I wasn't knowledgeable enough to understand what was being said at the time.

"Because SNS and PNS have been assumed to display coupled, reciprocal action on organ systems, increased vagal withdrawal was expected to be associated with an enhanced SNS response, producing a significant increase in heart rate and thereby stimulating fight or flight behaviors (Porges, 1995). However, we observed increased vagal withdrawal in combination with a decreased heart rate responsivity, the latter suggesting decreased SNS reactivity, although we did not measure SNS reactivity directly. This finding may be explained by research showing that the coupled activity of the two ANS branches may be either reciprocal or nonreciprocal, the latter entailing concurrent increases (coactivation) or decreases (coinhibition) in SNS and PNS activity (Berntson et al., 1991). Our finding of concurrent attenuated heart rate reactivity and increased vagal withdrawal, suggesting coinhibition, is in line with previous studies in which concurrent low levels of both PNS and SNS were found in relation to juvenile antisocial behavior"

So I was looking towards overstimulation, while the data suggested low vagal activity! I wouldn't have noticed that if you hadn't posted these excerpts, so thank you for your digging.

I just wanted to comment on this part of the article as well:

"Vagal tone. Another physiological mechanisms to account for the heart rate–antisocial relationship is increased vagal tone. Raine and Venables (1984) first suggested that the low heart rate recorded in antisocial individuals may be a function of increased vagal tone and reflect a passive coping response to mildly stressful situations (i.e., so-called ‘resting states’ prior to some other experimental manipulation). Data since then have not supported this hypothesis, favoring instead increased parasympathetic activity in antisocial individuals. For example, Mezzacappa et al. (1997) found that antisocial 15-yearold boys were characterized by low resting heart rates, but also found evidence for reduced, not increased, vagal functioning. Furthermore, Pine et al. (1996) found reduced, not increased, vagal tone was associated with aggressive behavior in children. If reduced vagal tone does prove a systematic correlate of antisocial behavior, it will indicate that the resting heart rate–antisocial relationship is driven by particularly strong sympathetic underarousal which is powerful enough to overcompensate for the lack of parasympathetic influences (low vagal tone) which would otherwise be expected to increase heart rate in antisocial children."

I wonder if by "antisocial" they are grouping people with violent behavioral issues with "traditional" calm and manipulative psychopaths. I mean, not all psychopaths exhibit aggressive behavior, which is why they tend to blend into our society so well, and not all people with aggressive tendencies completely lack empathy commonly associated with psychopathy, although they could be considered to be a subtype of psychopath, I suppose. Maybe some of the people who they label as antisocial really have aggressive behavior due to a higher SNS functioning than that of the PNS; I think it's hard to tell with the Antisocial Personality Disorder label. Also, I don't get how a low-functioning SNS can "overcompensate" for a low PNS and vagal tone. Do they mean to say that both nervous systems are underactive in psychopaths? Because I think that can be explained a bit better by what that other paper said about coactivation and coinhibition of the PNS and the SNS. I'm going to look up how exactly that's supposed to work when I have time.

The low vagal and noradrenergic functioning that this paper suggests could explain how psychopaths have little epinephrine and norepinephrine, because the stimulation of the vagus nerve is required for their release within the body, according to that SOTT article I mentioned before. Definitely worth looking into.

I think that the reduced right hemisphere functioning could definitely explain the lack of heart rate despite the low vagal tone, especially since there is so much evidence of psychopaths having structural problems on the right side of their brains. Does The Polyvagal Theory book mention anything about how physical damage to the right hemisphere could affect vagal activity? I know that there's a lot of mention about emotional trauma causing trouble within the right hemisphere, but I haven't been able to find anything regarding my inquiry yet.

When I find something relevant to the discussion, I'll be sure to post it. Again, sorry about sidetracking the thread.

[Biomiast]

Apologies for venturing away from the main idea of the thread, Biomiast. I have the habit of getting interested in new details, and then forgetting completely about what I was searching for in the first place. I'll try to be more considerate of that next time.

No need for apology, we have uncovered other things associated with psychopathy. I was interested in these details also, they are extremely important. But, as I said, there is nothing on hedgehog or oxysterols linked with psychopathy, so we should get back to place where we had more data.

Also, geez, I completely misinterpreted what you previously posted near the beginning of the thread, because I wasn't knowledgeable enough to understand what was being said at the time.

No, you did not misinterpreted. The researchers who discovered the low heart rate with psychopathy associate it with active vagus nerve which is something Adrian Raine, author of the last paper I quote, proposed. Yet, during later years, they have seen that high vagal activity is not associated with psychopathy, it is the opposite. So in the paper I quoted, they are looking for other explanations on low heart rate.

I wonder if by "antisocial" they are grouping people with violent behavioral issues with "traditional" calm and manipulative psychopaths. I mean, not all psychopaths exhibit aggressive behavior, which is why they tend to blend into our society so well, and not all people with aggressive tendencies completely lack empathy commonly associated with psychopathy, although they could be considered to be a subtype of psychopath, I suppose.

This was a common problem in almost every paper I have read on the subject. Everbody has a different sample group, some are "successful" psychopaths, some or violent criminals. Nobody is sure what to do with their sample groups and they interpret their results accordingly.


After getting deep into this topic, I can see the confusion within the literature. The best way seems getting the last updated information from review articles, but I will also look into noradrenergic functioning and low vagal activity.

[Biomiast]

Noradrenergic functioning got me thinking, and as I reviewed the article, I have found an enzyme that can convert dopamine to norepinephrine.  It is called dopamine β-hydroxylase. It is significant because we know psychopaths have more dopamine and less norepinephrine and this is the enzyme that converts one to the other. There are few studies that links psychopathy and antisocial behaviour with this enzyme, but they are there. There are also contrary studies, people saying it doesn't mean anything or they talk about some other disorders like substance abuse etc.

This is an abstract, I can not reach the full article.

An attempt is made to define the P dimension of personality in terms of its constituent traits, biological correlates, genetic bases, and relation to forms of psychopathology. Factor analyses revealed a coherent P supertrait incorporating the narrower traits of impulsivity, sensation seeking, lack of socialization and responsibility, autonomy, and aggression. Biological correlates of P dimension traits and some of the related types of psychopathology include poor conditionability, augmenting of the cortical evoked potential (EP), and low levels of the monoamine regulating enzymes monoamine oxidase (MAO) and dopamine-β-hydroxylase (DBH), the serotonin metabolite (5-HIAA), norepinephrine in the cerebrospinal fluid, and cortisol. P is related to high levels of gonadal hormones in males. More than half of the variance in P psychological traits and more than 80% of the variance in the correlated enzymes MAO and DBH is determined by heredity.

http://www.sciencedirect.com/science/article/pii/0191886989900044

[Megan]

...There are few studies that links psychopathy and antisocial behaviour with this enzyme, but they are there. There are also contrary studies, people saying it doesn't mean anything or they talk about some other disorders like substance abuse etc...

One has to wonder just how much deliberate confusion is being created.

[Laura]

...There are few studies that links psychopathy and antisocial behaviour with this enzyme, but they are there. There are also contrary studies, people saying it doesn't mean anything or they talk about some other disorders like substance abuse etc...

One has to wonder just how much deliberate confusion is being created.

Yeah.  The guy cited above with his nonsense about smoking and eating meats/fats was a real loser. 

[Biomiast]

...There are few studies that links psychopathy and antisocial behaviour with this enzyme, but they are there. There are also contrary studies, people saying it doesn't mean anything or they talk about some other disorders like substance abuse etc...

One has to wonder just how much deliberate confusion is being created.

Yeah.  The guy cited above with his nonsense about smoking and eating meats/fats was a real loser.

Actually I have found another article about vagal activity that contradicts the guy above. It basically separates agression into two types. One is Reactive aggression(RA) and the other is Proactive aggression(PA). Basically RA is defined as is "an angry response to perceived provocation" and it is what we see in violent people that fills up the prisons. It can also be referred as hot tempered aggression.  On the other hand PA is "a pre-meditated act used to achieve some goal" and it is associated with aggression of psychopaths. It is called cold tempered aggression. What the authors have found is, both autonomic responses and vagal activity is different in children which has PA as opposed to RA. It says PA uses increased vagal activity and RA uses decreased vagal activity. To sum up the whole point:

Thus, individuals with a tendency to respond to stress with an angry or defensive response, for example, may be more likely to use RA when faced with provocation or frustration. Conversely, PA may be characterized by increased vagal or parasympathetic control of the heart (reflected in increased Heart Rate Variability) and heightened Skin Conductance level, which may reflect increased frontal lobe activity and subsequent emotional control. Nonetheless, PA is associated with hyperactivity/impulsivity, which may interfere with effortful control of aggressive impulses or learning from punishment. Thus, individuals with a tendency to value instrumental over social goals, but with low effortful control, may be more likely to use PA when presented with the possibility of instrumental gain. A focus on using aggression for instrumental gain may also reflect a risk for chronic and persistent behavioral difficulties.

http://www.vu-ams.nl/fileadmin/user_upload/publications/Scarpa_2010.pdf

This is a more recent paper, so perhaps it is more reliable?

And for the initial comments, I am pretty confused reading all these contradicting findings. Yesterday I found the paper above and I was like 

[Daenerys]

Unfortunately, I do not know of anyone studying psychopathy who is applying the model [polyvagal theory].  However, the theory might identify sluggish removal of the vagal brake and an associated dampened sensitivity to danger, all of which could be associated with a "faulty" neuroception.  Basically, the detection of features of danger in the environment and expressed in other people (i,.e., the interpretation of intention of biological movement) might be faulty or dampened.

Interestingly enough, Toxoplasma also dampens sensitivity to danger (and even increases its attraction). The same happens with "women who love psychopaths" or other wounded and traumatized individuals. Their sensitivity and awareness are dampened, and this fact makes them an easy pray for psychopaths.

After watching this documentary about Toxoplasma, I wonder if there is any connection between parasite induced and predator specific "unwiring" in amygdala (that dampens one's sensitivity to danger and predators) and undeveloped amygdala in psychopaths. It just too much of a coincidence to think that it isn't related in some way. It's like there is some sort of dynamic that puts the predator and its pray on the same "wavelink": one is a hook and the other plugin. And what is more amazing, who knows if there isn't some sort of intraspecies connection between these two types of predators. But it's obviously just speculation.

The good news that since in the case of "prey" it's an induced and not genetic or permanent condition like with psychopaths, perhaps EE and vagal nerve activation in general (apparently toxoplasma "invades" vagus nerve and affects its functions), coupled with anti-parasite treatment and high fat diet may help with canceling the effect? The same documentary mentions the idea of who knows what other parasites are out there that may also affect human behavior, so perhaps we are looking here at multilevel "predatory invasion", where bad diet makes an opening and fertile ground for parasite infection, and they in their turn make the person more susceptible for higher level predation.

By the way, one other toxoplasma related symptom that was mention in the documentary is impulsivity, which is also one of psychopathy traits. So maybe in case of toxoplasma and other parasites, Castaneda's words about predators giving us their minds should be taken quite literally!

OMG! I had this in my early 20's. The doctor called it also cat scratch syndrome though. My neck ( left lymph node) was so swollen I could not turn my head- they had to drain it twice. I have always had cats- I have four now. I have not yet watched this documentary but I am about to. Wow.

[Biomiast]

Hi to all,

Last year, I left this thread with much confusion and frustration because of conflicting research done by psychologist. Now, I have more time to deeply look at what was being done and I should come back and tidy up this thread. I will describe a model for the vagus nerve connection which was outlined before thanks to zlyja and Gawan.

First of all, I have read an article on vagal tone research which showed me that researchers use the term vagal tone with liberty and tell there is an increase in vagal tone, even when there can be other causes to explain it. For this reason, I leave out the data associated with vagal tone. I am sorry for the confusion I have created. For more information, check out this paper:

http://www.ncbi.nlm.nih.gov/pubmed/11393643

Psychopathy, which is associated with reward seeking and faulty inhibition mechanism can be explained best with the enzyme called dopamine beta hydroxylase which converts dopamine into norepinephrine. This is significant because dopamine is associated with reward and the more dopamine you have, more driven you are to reach to a reward. I posted the article before, but here it is:

http://www.sciencedirect.com/science/article/pii/0191886989900044

Another article was also showing psychopaths have much more dopamine responses to rewards:

http://www.bmedreport.com/archives/10558

This dopaminergic system has also shown to be much more active in psychopaths, as evidenced by their enlarged striatum and very active nucleus accumbens.
 
And you may ask, a lot of people are goal driven, why are psycopaths like that remorseless monsters. The reason lies with norepinephrine. Since dopamine beta hydroxylase can not convert dopamine to epinephrine, a psycopath's brain swims with dopamine and lacks norepinephrine. And norepinephrine is an inhibitory signal telling us to stop when we see something negative, telling us to question ourselves etc. Brain's inhibition system is dependent on a brain region called locus coerolous which is composed of neurons that use norepinephrine to relay a signal to amygdala. If there is no epinephrine, there is no signal that says stop to a psychopath and you would get a machine with underdevelopped inhibitory system.

And how this all ties with the vagus nerve? Dopamine beta hydroxylase deficiency is associated with hypoglycemia which shows the connection with vagus nerve as outlined by zlyja and Gawan.

Gawan said aggressive individuals are hypoglycemic and blood sugar swings can damage vagus nerve. Zlyja found the article where it showed only myelinated vagus nerve is damaged when a person is hypogylcemic.

http://www.ncbi.nlm.nih.gov/pubmed/15549329

This ties well with what Approaching Infinity said that psychopaths' mammalian vagus is not doing its job for engaging and social behaviour because it is myelinated and it is damaged due to hypoglycemia. And, cardiac activity deceleration observed in aggressive individuals is primarily affected by reptilian vagus. And even the functioning of that vagus is faulty. When you are in panic or any other negative emotion, vagal withdrawal occurs because you are no longer calm, and you accelerate your heart to compensate the energy for the intense experience you are living. Since psychopaths are not responsive to aversive stimuli because of their norepinephrine, there is not a complete vagal withdrawal. I suppose this was what Porges meant when he said sluggish removal of vagal brake.

I wonder the reason that dopamine beta hydroxylase is associated with hypogylcemia is this over activity of vagus nerve which causes insulin secretion as Gawan said. Very interesting.

During my research, I have come up with a few hits, but these are not associated with above mechanisms, I am sharing them if it rings any bell.

First of all 5-HIAA which is a metabolite of serotonin is found less in aggressive individuals. MAO genes which are associated with reactive aggression are required to make 5-HIAA. I don't know if there is less serotonin in these individuals or if serotonin is normal, but can not be converted to 5-HIAA because of low activity MAO genes.

The other hit is a transcription factor called tailless which is associated with the formation of forebrain development. Mice that doesn't have this gene is shown to be aggressive and decrease in maternal behaviour.

http://www.ncbi.nlm.nih.gov/pubmed/12527005

http://cercor.oxfordjournals.org/content/13/9/921.full

The other hit is an enzyme called Fatty acid amide hydrolase which causes an increase in striatum and decrease in amygdala activity in psychopaths, again reward pathways are more active than inhibition pathways. This enzyme is associated with the metabolism of cannabioids which are a chemical class that is associated with social behaviour and pain.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794920/

[Laura]

Another possible clue:

Does low serum cholesterol cause psychopathy?

Strange as it may seem, low cholesterol could be a significant factor, maybe even the cause, of psychopathy.

I got to thinking about this as a result of reading an article about psychopathy in the current New Yorker,(http://www.newyorker.com/reporting/2008/11/10/081110fa_fact_seabrook) in which we learn about a psychological researcher named Kent Kiehl, who is using MRI scans to study the brains of imprisoned psychopaths.

   

To date, Kiehl has scanned ninety adult psychopathic brains with the portable scanner. The data, he says, confirm his hypothesis that psychopathy corresponds to a deficit in the paralimbic region. “If you put the pictures of the psychopaths’ brains next to the control group, it’s obvious,” he told me.

The paralimbic region of the brain is responsible for memory formation as well as mediating negative emotional states, such as guilt. (http://linkinghub.elsevier.com/retrieve/pii/S0006322300002511)

Cholesterol-lowering statins have been implicated in many serious cases of memory loss. (http://www.spacedoc.net/662_cases_memory_loss) It works like this:

   

Our brain's synapses for memory formation cannot function without sufficient cholesterol and since the LDL/cholesterol molecule is much too large to pass the blood/brain/barrier, nature had devised an alternative means of supplying the brain with necessary cholesterol.

    Pfrieger found that the housekeeping cells of the brain, known as glial cells had taken over the role of cholesterol synthesis. It seems likely that the inhibitory effect of statin drugs on cholesterol synthesis extends to our glial cells, and this might account for the many varieties of cognitive dysfunction reported.

Furthermore, low cholesterol and violence - including homicide, suicide, and accidents - are associated, strongly enough that it's unlikely to be a coincidence. (http://psychservices.psychiatryonline.org/cgi/content/full/49/2/221) Whether the association is merely that, or whether low cholesterol is a causative factor, is another question. But given that cholesterol plays a critical role in neuronal function, including the formation of memories, it appears that a logical link between cholesterol and violence exists. Low cholesterol levels are linked to low serotonin levels in the brain, which has significant associations with violence, suicide, and depression. (http://www.advancedhealthplan.com/lowercholestrol.html)

Lastly, we have a study carried out in Finland, Total serum cholesterol level, violent criminal offences, suicidal behavior, mortality and the appearance of conduct disorder in Finnish male criminal offenders with antisocial personality disorder. ("Antisocial personality disorder" is a euphemism for psychopathy.)

   

Associations between low total serum cholesterol (TC) levels and antisocial personality disorder (ASPD), violent and suicidal behavior have been found. We investigated the associations between TC levels, violent and suicidal behavior, age of onset of the conduct disorder (CD) and the age of death among 250 Finnish male criminal offenders with ASPD. The CD had begun before the age of 10 two times more often in non-violent criminal offenders who had lower than median TC levels. The violent criminal offenders having lower than median TC levels were seven times more likely to die before the median age of death in the study material. The violent offenders having lower than median TC levels were eight times more likely to die of unnatural causes. The mean TC level of these male offenders with ASPD was lower than that of the general Finnish male population. Low TC levels are associated with childhood onset type of the CD, and premature and unnatural mortality among male offenders with ASPD. The TC level seems to be a peripheral marker with prognostic value among boys with conduct disorder and antisocial male offenders.

That's about it. Low cholesterol is strongly associated with criminality, as is psychopathy. At least one prominent researcher in the field of psychopathy believes that psychopaths have a defect in the paralimbic system, which is responsible for memory and negative emotions such as guilt. Psychopaths notoriously do not suffer from guilt. Cholesterol-lowering drugs can cause memory loss and aggression. Therefore, low serum cholesterol is implicated in psychopathy. Q.E.D.

Now the question is, just how much is heredity and how much environmental? Is the widespread and longstanding recommendation to cut the fat out of our diets and to ensure a low cholesterol level causing an increase in the number of psychopaths? (If it is, those low-fat diet folks have a lot to answer for, more than they ever would have dreamed.) Does the widespread prescribing of statins increase the fraction of psychopaths in the population? Wouldn't surprise me. (http://www.spacedoc.com/statins_aggressiveness.html)

[Megan]

...First of all, I have read an article on vagal tone research which showed me that researchers use the term vagal tone with liberty and tell there is an increase in vagal tone, even when there can be other causes to explain it. For this reason, I leave out the data associated with vagal tone...

I have wondered about the use of vagal tone as a measure as well. It comes across to me in the (limited) reading I have done as a convenient measure of we-don't-know-what. It seems to be taken as a kind of summary of the state of a large number of individual fibers in the bundle, running in two directions. I suspect, though, that there is a good reason for having all of those individual fibers and the messages that they carry or else evolution would have long ago consolidated them. I wonder if it is a bit like evaluating general health by measuring body temperature.

[Megan]

...Now the question is, just how much is heredity and how much environmental? Is the widespread and longstanding recommendation to cut the fat out of our diets and to ensure a low cholesterol level causing an increase in the number of psychopaths? (If it is, those low-fat diet folks have a lot to answer for, more than they ever would have dreamed.) Does the widespread prescribing of statins increase the fraction of psychopaths in the population? Wouldn't surprise me. (http://www.spacedoc.com/statins_aggressiveness.html)...

It might increase the fraction of old, fat, sickly psychopaths, anyway. (And I did know one of those.) But then statins are being pushed on children now, "for their health." So it's a very good question.