Representation of Time and Motivation in the Nervous System

Abstract

Much of our conscious experience comes from objects that exist purely within the brain – abstractions – making them extremely challenging to study. But we know (or think we know) most of their fundamental building blocks: cells like neurons and glia, processes like biochemistry and electrophysiology, and their combinations and interactions. It still remains to be shown how these ideas can be stitched together to represent entities seemingly more complex and abstract than the constituent parts, and especially to experimentally verify that these apparent representations are used in the way we think. In this work, I study a number of abstractions (the passage of time, the accumulation of evidence, and the competition of several motivations), demonstrate how they arise in a relatively simple system (copulating Drosophila) to direct behavior, and propose a set of frameworks for extending these findings to more general circumstances. I find that the representation of abstractions does not come from studying single perspectives, e.g. population coding or measurements of synaptic strength, but instead from a holistic perspective of the operation of neurons. The brain simultaneously uses every stratum of its organizational structure, from the genetic up to ensembles of neurons acting in networks, to produce and transform the abstractions that control our behavior and experience.