Economic Decision Making and Neural Correlates of Subjective Value in the Nematode Worm, Caenorhabditis elegans
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Decision making is pervasive in nature. Organisms from across the phylogenetic spectrum take in information from the external world and pursue courses of action in an attempt to maximize their evolutionary fitness. When faced with several competing alternatives, an individual must decide which option to select or how to distribute their resources amongst the various alternatives. The relatively young field of neuroeconomics has sought to reconcile economics' mathematical tools and formal models of decision processes with physiological measures from the nervous system. How individuals assess the value of competing options and act on internal representations of value is now a major focus of neuroeconomics and systems-level neuroscience. However, experiments in humans and non-human primates face barriers to progress that would be ameliorated in a genetically tractable organism with a compact nervous system. The nematode worm Caenorhabditis elegans has a relatively simple nervous system and a host of genetic tools, making it an advantageous system to elucidate the neural basis of decision making. This dissertation makes several contributions towards establishing C. elegans as a model of value-based decision making. I first develop a behavioral test for C. elegans that parallels paradigms of value-based decision making in human economics. Using microfluidic environments coupled with electrophysiological measures of feeding behavior, I offer worms discrete food choices and monitor how they distribute their 'budget' (i.e., feeding) between the alternatives. By manipulating the relative price (i.e., ease of consumption) of each food, I found that worms alter their spending patterns just as a human consumer does, expanding their consumption of a food as it becomes relatively cheaper. I also found that worms maintain a transitive rank order in their choice preferences, adhering to a classical test of economic rationality. Finally, I show that sensory neuron AWC is necessary for wildtype decision making, and monitor its activity during simulated decision making. AWC is active on the timescale of decision making, but its sensitivity does not fully explain C. elegans food preferences. These results suggest that the representation of value is distributed across a network whose aggregate activity in turn drives value-based decision making in C. elegans.