This week’s Journal of Neuroscience featured an article from a recently emerged, yet rapidly progressing branch of neuroscience: neuroeconomics. As implied, neuroeconomics aims to elucidate neural circuits and structures responsible for making risky (and safe) economic choices. In this particular study, a group of Manhattan researches gauged risk aversion in food and water-deprived subjects who were offered (either freely or through gambling) money, food (sweet or salty snack of M&Ms or Ritz crackers without any interchange), and/or water (Fiji or Smart Water, I hope). The complex experimental design is presented below.
In brief, subjects were guaranteed to receive a small amount of a particular reward or they could gamble to receive a larger amount of the same or different reward. As anticipated in the case of monetary rewards, the subjects’ risk aversion (unwillingness to gamble) was based on both the probability of receiving a larger sum of treats and the magnitude of the sum; such that, if the probability was considerably high (50%), subjects would more often gamble for additional money regardless of the percent increase from the guaranteed earning of two bucks rather than be assured the extra two bucks. The subjects would also gamble for additional money if the percent increase from two bucks was significantly (such as 1000%) higher. Despite all the careful analyses that this paper presented, I wish that there would have been more emphasis on how these types of risk aversion behaviors change when a different type of reward was up for grabs (such as food or water) and how the extent of risk aversion (or lack of it) correlated with hunger and thirst levels. Data showing these trends were presented for the subjects in the “same-type” group, however.
The elegances of this study also reside in the mapping of brain activity during these tasks. Risk aversion associated with food rewards activated subcortical, hypothalamic areas of the brain which is not surprising given that the primary neural centers that regulate feeding (arcuate nucleus; lateral hypothalamus) reside here. Risk aversion associated with monetary and water rewards activated more neocortical regions, which is surprising particularly for risk aversion associated with water since water, unlike money, is a primary reward, meaning that it is necessary (at least, biologically) for survival, and therefore, would have been predicted to be linked to heightened activity in more subcortical, archaic regions of the brain much like food. Although, there was overlap between cortical pathways associated with monetary risk aversion and secondary pathways linked to food risk aversion.
In summary, I enjoyed reading this paper because the hypotheses under investigation align with theories that have recently emerged in the circadian field in regards to the existence of primary (food) and secondary (drugs of abuse)-sensitive oscillators that lie outside the master pacemaker, but yet entrain rhythms. I am not a proponent of these theories, but that can be saved for another post…..
Levy DJ, & Glimcher PW (2011). Comparing apples and oranges: using reward-specific and reward-general subjective value representation in the brain. The Journal of neuroscience : the official journal of the Society for Neuroscience, 31 (41), 14693-707 PMID: 21994386