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]