Graded Encoding of Food Odor Value in the Drosophila Brain Jennifer Beshel and Yi Zhong
J. Neurosci. 2013;33 15693-15704
Odors are highly evocative, yet how and where in the brain odors derive meaning remains unknown. Our analysis of the Drosophila brain extends the role of a small number of hunger-sensing neurons to include food-odor value representation. In vivo two-photon calcium imaging shows the amplitude of food odor-evoked activity in neurons expressing Drosophila neuropeptide F (dNPF), the neuropeptide Y homolog, strongly correlates with food-odor attractiveness. Hunger elevates neural and behavioral responses to food odors only, although food odors that elicit attraction in the fed state also evoke heightened dNPF activity in fed flies. Inactivation of a subset of dNPF-expressing neurons or silencing dNPF receptors abolishes food-odor attractiveness, whereas genetically enhanced dNPF activity not only increases food-odor attractiveness but promotes attraction to aversive odors. Varying the amount of presented odor produces matching graded neural and behavioral curves, which can function to predict preference between odors. We thus demonstrate a possible motivationally scaled neural “value signal” accessible from uniquely identifiable cells.
“In characterizing the specificity of dNPF activity to specifically food-odor attraction behavior, we are able to support the idea that there may be discrete value-processing centers specialized to assess only a particular type of stimulus, even within the fly brain. We speculate that separate sets of neurons may responsible for, for example, sex-related value and thus mediate attraction behavior to the pheromone cVA, whereas other neuronal subsets may be responsible for attraction to other categories of odors.”
My Comment: Sex-related value and attraction behavior to the pheromone cVa is nutrient dependent because nutrients are metabolized to species-specific sex pheromones. Thus, the graded encoding of food odor value in the Drosophila brain extends well to the graded encoding of nutrient-dependent species-specific pheromones that control reproduction in species from microbes to man via conserved molecular mechanisms. There’s a model for that!