Sex and Money on the Brain

Back in 1991, Mark Knopfler sang

"Sex and money are my major kicks
Get me in a fight I like the dirty tricks"
Now twenty years later a team of French neuroscientists have followed up on this observation with a neuroimaging study: The Architecture of Reward Value Coding in the Human Orbitofrontal Cortex.

Sescousse et al note that people like erotic stimuli, i.e. porn, and they also like money. However, there's a difference: porn is, probably, a more "primitive" kind of rewarding stimulus, given that naked people have been around for as long as there have been people, whereas money is a recent invention.

The orbitofrontal cortex (OFC) is known to respond to all kinds of rewarding stimuli, but it's been suggested that the more primitive the reward, the more likely it is to activate the evolutionarily older posterior part of the OFC, whereas abstract stimuli, like money, activate more anterior parts of that area.

While this makes intuitive sense, it's never been directly tested. So Sescousse et al took 18 heterosexual guys, put them in an fMRI scanner, showed them porn, and gave them money. Specifically:
Two categories (high and low intensity) of erotic pictures and monetary gains were used. Nudity being the main criteria driving the reward value of erotic stimuli, we separated them into a “low intensity” group displaying women in underwear or bathing suits and a “high intensity” group displaying naked women in an inviting posture. Each erotic picture was presented only once to avoid habituation. A similar element of surprise was introduced for the monetary rewards by randomly varying the amounts at stake: the low amounts were €1-3 and the high amounts were €10-12.
You've gotta love neuroscience. Although the authors declined to provide any samples of the stimuli used.

Anyway, what happened?
As hypothesized, monetary rewards specifically recruited the anterior lateral OFC ... In contrast, erotic rewards elicited activity specifically in the posterior part of the lateral OFC straddling [fnaar fnaar] the posterior and lateral orbital gyri. These results demonstrate a double dissociation between monetary/erotic rewards and the anterior/posterior OFC ... Among erotic-specific areas, a large cluster was also present in the medial OFC, encompassing the medial orbital gyrus, the straight [how appropriate] gyrus, and the most ventral part of the superior frontal gyrus. [immature emphasis mine]
In other words, the posterior-primitive, anterior-abstract relationship did seem to hold, at least if you accept that money is more abstract than porn. (Many other areas were activated by both kinds of rewards, such as the ventral striatum, but these were less interesting as they've been identified in many previous studies.)

Overall, this is a good study, and a nice example of hypothesis-testing using fMRI, which is to be preferred to just putting people in a scanner and seeing which parts of the brain light up in a purely exploratory manner...

ResearchBlogging.orgSescousse G, Redouté J, & Dreher JC (2010). The architecture of reward value coding in the human orbitofrontal cortex. The Journal of neuroscience : the official journal of the Society for Neuroscience, 30 (39), 13095-104 PMID: 20881127

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