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Food, sex and frontal dementia
A team of French researchers headed by Jean-Claude Dreher of the Centre de Neuroscience Cognitive in Lyon, France, has provided the first evidence that the orbitofrontal cortex (located in the anterior ventral part of the brain) contains distinct regions that respond to secondary rewards like money as well as more primary gratifications like erotic images.
The orbitofrontal cortex is so-called, because it’s the area of prefrontal cortex near the orbits of the eye.
This finding has been published in the Journal of Neuroscience: : G. Sescousse, J. Redouté, J-C Dreher (2010) The architecture of reward value coding in the orbitofrontal cortex. J Neurosci, 30 (39)
The paper is available here.
Guillaume Sescousse, Jérôme Redouté, and Jean-Claude Dreher.
There could be a dissociation between so-called “primary” rewards, such as food or sex, which satisfy basic vital needs and have an innate value, and more “higher order” rewards such as money or power, which are not essential for survival and whose value is assessed by association with primary rewards. I note the paper calls them “secondary” not “higher order”, but actually I feel that, as there is such a complex inter-relationship between different “secondary” rewards, “higher order” is a safer term.
To verify these hypotheses, Jean-Claude Dreher and Guillaume Sescousse conducted an original experiment in the form of a game that rewarded 18 volunteers with money or erotic images, while their cerebral activity was monitored using an fMRI functional magnetic resonance imaging scanner. The experiment showed that the rewards are indeed evaluated in partially shared cerebral regions, namely the ventral striatum, insula, mesencephalon and anterior cingulate cortex.
The researchers have also confirmed that there appears to be a dissociation between primary and secondary rewards in the orbitofrontal cortex. Its posterior region (more primitive) is specifically stimulated by erotic images (a primary reward), while its anterior region (which is more recent in man) is activated by monetary gain (a secondary reward). The more abstract and complex the reward, the more its representation stimulates the anterior regions of the orbitofrontal cortex.
The results are interesting because, arguably, they provide the first evidence of a dissociation in the brain between two types of reward, suggesting the existence of distinct regions corresponding to various gratifications. Dreher and Sescousse themselves propose that this research could lead to a better understanding of certain psychiatric disorders, including gambling addiction.
However, the most striking observation for me was the fact I have long felt that the brain reward systems go badly awry in early behavioural variant frontotemporal dementia. It has long been a mystery why such patients suddenly develop an otherwise predilection appetite for sweet foods and drinks (including chocolate and Crest lemonade), and why a minority of patients become overtly hypersexual and disinhibition.
I provided detailed descriptions of patients of Prof John Hodges at Cambridge in my paper in Brain from 1999, which has become a classic in its own right, with almost 250 international citations. It is likely that pathology in the orbitofrontal cortex is one of the earliest hallmarks of this condition, a finding that has been well embraced in the intervening decade.
I therefore welcome enormously this research contribution by , and look forward to a similar fMRI study in behavioural variant frontotemporal dementia.
Dr Shibley Rahman, PhD FRSA LLB(Hons)
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