In the last edition of Science. Zhang et al. examine the decision-making mechanisms of fruit flies (Drosophila). They used mutant flies to see if dopaminergic systems are necessary for saliency, or value-based, decision-making. Value-based decision-making is contrasted with perceptual, or simple, decision-making. In the former, decision in made only by integrating sensory cues: in the latter, some value is added to available options. Values are especially important when there are conflicting evidence of ambiguous stimuli.
As many researches show, dopaminergic (DA) systems are an important--maybe the most important--valuation mechanism. They link stimuli to expected value. Flies, bees, monkeys and humans all rely on DA neuromodulation to make decisions. Fruit flies provides an interesting opportunity for neuroeconomics: it allows scientists to create genetic mutants (in this case, flies whose DA system shuts off over 30° C.) and analyse their behavior. Zhang and its collaborators discovered that flies without DA activity are able to make decision when they face a well-known situation, where it is easy to choose, but are inefficient when they face conflicting stimuli. Hence, when valuation is needed, DA is required: no DA, no valuation, no value-based decision-making.
Conceptually, the study shows how the concept of value-based and perceptual decision-making can be separated. The 'simple heuristics' and ecological rationality program made a strong case for simple decision-making: you just "see" the best option, e.g. which city is bigger: Munich or Dortmund? Since the size of a city is correlated with its exposition in media, it is easy to answer by using a simple heuristics (choose the most familiar). In this case, there is no need to evaluate options. But when you have to choose where you want to live, values are important. In this case you heed preference ranking, and preferences seems inherently tied to DA activity.