Mixing Memory

Anyone who's ever taken a bite of a Reese's Peanut butter Eggs that are only sold during the Easter season knows that chocolate is a mood enhancer, but in case you thought it might just be the wonderful taste, there is actual empirical evidence that chocolate can elevate your mood. Specifically, eating chocolate appears to make individuals suffering from atypical depression and seasonal affective disorder (SAD) feel better. As a result, chocolate and carbohydrate cravings are common in atypical depression and SAD, perhaps as a form of self-medication¹. Several hypotheses have been offered to explain this effect, the most well-known of which argues that eating chocolate helps to regulate serotonin levels. Since a low serotonin level is one cause of depression, it stands to reason that depressed individuals would crave foods that might increase their serotonin levels. Other explanations include (from the summary of the paper, linked below):

• corrects a deficiency in the regulation of mood


• is highly pleasurable


• is addictive


• is a means of coping during a negative mood.

An article by Parker et al. in the June issue of the Journal of Affective Disorders the various proposed explanations for the effects of chocolate on mood². You can read a summary of the paper here. Parker et al. find each of the proposed explanations wanting. For example, the serotonin hypothesis suffers from two major problems. The first, and most obvious, is that the potential increase in serotonin level resulting from eating chocolate wouldn't occur fast enough to explain the immediate elevation in mood. The second is that chocolate's protein content is too high for the body to be able to get the building blocks of serotonin from it. Furthermore, they find in their review that while chocolate can produce a short-term elevation of mood, when people eat too much chocolate (as they often do when they are craving it), their mood soon drops below it's pre-eating level. So, chocolate doesn't make a very good anti-depressant, and it's not really clear why it produces temporary elevations in mood for some people.

On a related note, one of the papers cited in the Parker et al. review is particularly interesting, not so much because of the results, but because of the methods. Small et al³ had hungry participants eat squares of chocolate until they were full, and then keep eating. As they ate the chocolate, they rated how pleasurable the chocolate was, and underwent PET scans each time their ratings dropped 2 points on a 20 point scale (from -10, awful, to +10, delicious). The purpose of the study was to observe differences in brain activity for approach motivations (when they are hungry and want chocolate) and avoidance motivations (when they're so full they feel like they're going to puke), and they found such differences. If you're interested, when eating chocolate was still pleasurable, increased blood flow was observed in the caudomedial orbitofrontal cortex, subcallosal region, insula, striatum, and , while unpleasurable eating resulted in increased activity in the parahippocampal gyrus, caudolateral orbitofrontal cortex, and prefrontal regions, which the authors argue confirms "that there are two separate motivational systems: one orchestrating approach and another avoidance behaviours." That's interesting and all, but who cares? Forcing people to eat chocolate until they say that "eating more would make me sick" is torture in the name of science on par with forcing smokers to go hours without cigarettes, and then having them light one up and hold it, but preventing them from smoking it while they perform experimental tasks.

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¹Wurtman, R.J., Wurtman, J.J., 1989. Carbohydrates and depression. Scientific American, 260, 68-75.
²Parker, G., Parker, I., & Brotchie, H. (2006). Mood state effects of chocolate. Journal of Affective Disorders, 92(2-3), 141-148.
³Small, D.M., Zatorre, R.J., Dagher, A., Evans, A.C., Jones-Gotman, M., 2001. Changes in brain activity related to eating chocolate. From pleasure to aversion. Brain, 124, 1720-1733.