Social status, novelty-seeking, and dopamine

Dopamine sure seems to do a lot of things these days, doesn’t it? It’s most commonly thought to be the mechanism for prediction error which is used for reward-based learning, but it is also linked to sociability, pain, and a ton of other things.

One of its mechanisms relates to social dominance. Eight years ago, Morgan et al. published a paper concerning social dominance in monkeys. They wanted to show how there is a profound environmental influence on dopamine function, so they separated monkeys into housing blocks of four apiece. Whereas before there was little difference in dopamine (D2) levels between monkeys, after three months of living together the monkeys that had become dominant showed a more than 20% increase in dopamine receptor density, with the most submissive showing no change. Unrelated to our point, but still interesting, they also showed that the submissive monkeys were much more inclined to self-administer cocaine; the dominant monkeys were much less likely to do so.

Dopamine receptor density is therefore an environmental and cultural phenomenon – at least in monkeys. What about people? It turns out we’re pretty much the same way. If you do the same PET scan on people that you did on monkeys, their dopamine level (D2/3 in the striatum) correlates (r^2 ~ 0.5) with a measure of human social status. So we’re not that different, after all. Just remember it’s not dopamine that drives dominance, but dominance that drives dopamine. Why? Who knows?

Dopamine levels in the same area are related to other aspects of behavior besides just dominance. If you perform the same measure of dopamine receptor availability but compare it to sensation-seeking, or novelty seeking, you get an altogether different type of curve. Here we instead see an inverted U-shaped curve. Using modeling, they suggest that those with the greatest need to seek sensational activities have both low receptor availability and high dopamine occupancy. I suppose the low-sensation seekers have low receptor availability and low dopamine occupancy (ie, few binding sites along with a lower volume of dopamine to bind).

Are these two phenomena related? They both look at the receptor availability of a certain population of dopamine receptors (D2/3). But just because the dopamine receptors are the same and in roughly the same place doesn’t mean the connectivity is the same. Are these all the same circuit? Does dominance affect novelty-seeking? Someone really needs to find an animal model to start testing these propositions.

Gjedde, et al., 2010. Inverted-U-shaped correlation between dopamine receptor availability in striatum and sensation seeking. Link.

Martinez, et al. 2010. Dopamine type 2/3 receptor availability in the striatum and social status in human volunteers. DOI

Morgan, et al. 2002. Social dominance in monkeys: dopamine D2 receptors and cocaine self-administration. Link.

[monkey photo from]

Taekwondo monkeys are, unsurprisingly, a recipe for disaster

Hu Luang, 32, a bystander who photographed the incident, said: “I saw one punch him in the eye – he grabbed another by the ear and it responded by grabbing his nose. They were leaping and jumping all over the place. It was better than a Bruce Lee film.”

At one point the monkey trainer grabbed a staff to hit the monkeys, only to find himself facing a stick-brandishing monkey that cracked him over the head.

Merry Christmas.

Monkey music has a whole new meaning

I don’t have much to add to this:

Previous experiments have shown that tamarin monkeys prefer silence to Mozart, and they don’t respond emotionally to human music the way people do. But when a psychologist and a musician collaborated to compose music based on the pitch, tone and tempo of tamarin calls, they discovered that the species-specific music significantly affected monkey behavior and emotional response….“If we play human music, we shouldn’t expect the monkeys to enjoy that, just like when we play the music that David composed, we don’t enjoy it too much.”

Click the above link to listen to clips of the songs they played to the monkeys. ‘Song’ has been seen in birds, whales, and gibbons (and humans), but that’s it. If you read the original research article (in Biology Letters), they mention that cotton-top tamarins and marmosets prefer slow tempos but are indifferent to human music; the question that they tried to answer was why the monkeys would be responsive to tempos and not music. When are we going to create the academic field of ‘non-human culture’?

Drunken monkeys

A recent New York Times article discussed alcohol consumption in animals. An amusing and important topic for all of us, I would highly suggest reading the comments to find out more about this delightful subject. Did you know that some pigs have been known to make alcohol by leaving some of their feed untouched, allowing it to ferment? Those clever bastards.

This leads me to something I’ve been meaning to talk about for a while: the drunken monkey hypothesis. Let’s say that you were a scientist who wanted to study why animals consumed alcohol. How would you go about this? Apparently, you would literally wander through a jungle, picking fruit up off the ground and throwing rocks at trees in order to knock it down. Then you would compare the amount of alcohol (ethanol) in the fruit.

What this group found was that the pulp of slightly overripe fruit, such as that drunkenmonkeyfound fallen from branches, had a high level of ethanol (an average of 4.5%). They suggest that this helps ward off bacterial invasion, allowing the fruit to stay fit for consumption longer and thus promoting seed dispersal by foragers. They also think that consumption of ethanol has an appetitive effect, so the animal would feel hungrier. Evidence from fruit-eating animals show that they can clear the alcohol from their systems much faster (with much more active alcohol dehydrogenase) than their non-fruit-eating brethren.

I guess the evolutionary idea is that we now associate alcohol consumption with nutritional reward. Alcoholism would then be akin to obesity: a problem of nutritional overconsumption. I’m not sure how much I agree with it; it would seem that the side-effects of alcohol would be a stronger determinant of enjoyment than the taste. But then, maybe that was the coevolutionary strategy? ie, you get drunk but you have to eat healthy first! Probably not, but entertaining nonetheless.