Project Summary/Abstract (Unchanged from the funded parent award) The idea that information processing depends on neuronal firing rate (rate coding) has long been a central dogma in neurobiology. However, other non-canonical coding schemes (temporal and “analog” codes) have been proposed to carry meaningful information and be more computationally powerful than rate coding. Importantly, the field has lacked powerful genetic model systems to disentangle non- canonical coding processes, and I addressed this gap by defining two neural circuits in Drosophila that can be used to study temporal and analog codes. I found that temporal coding underlies the circadian regulation of sleep in the Drosophila DN1p clock neurons, whereas analog and potentially “hybrid” (analog + spiking) codes are used to achieve axon-specific hunger processing in Drosophila DA-WED feeding neurons. As a model system to understand how spiking temporal codes impact molecular signaling and behavior, we will focus on Drosophila DN1p clock neurons having specific spiking patterns to control sleep quality through a novel form of synaptic plasticity, SPDP (Spike Pattern Dependent Plasticity). To examine the molecular process of SPDP formation, we will first characterize essential elements of the temporal structures within irregular spiking patterns in DN1ps, as well as identify their biophysical origins. Next, we will investigate molecular mechanisms that act downstream of presynaptic spiking patterns to transform electrical signals into biochemical responses. We will also leverage the power of Drosophila genetics to delineate the entire molecular pathway required for SPDP in DN1ps synapses. As a model system to understand how nonspiking neuronal codes impact signaling and behavior, we will focus on Drosophila DA-WED feeding neurons having local plasticity to control protein hunger behavior. Neural coding paradigms have generally focused on “digital” all-or-none spike-based models. In mammals, pure “analog” coding occurs in the retina, but recent work has shown that analog signaling modulates spike-based signaling (“hybrid” coding) in the hippocampus and cortex. However, the function of these codes in neural plasticity and behavior remains unclear. We recently discovered that the “protein coding” axonal branch, but not the “sugar coding” axonal branch, exhibits sub-threshold membrane potential fluctuations of DA-WED feeding neurons, following mild protein deprivation. Following severe protein deprivation, such analog signaling interacts with spiking events to generate “hybrid” processing to achieve stronger and longer-lasting protein feeding behavior. Thus, we will study the molecular processes mediating “analog” and “hybrid” signaling and how “hybrid” codes may underlie localized branch-specific plasticity. In conclusion, these studies using Drosophila DN1p clock neurons and DA-WED feeding neurons should elucidate fundamental principles for non-canonical neural codes, determine the role of these neural codes in long-lasting behaviors and plasticity, and identify their underlying molecular mechanisms.

Project Narrative (Unchanged from the funded parent award) We focus on studying non-canonical forms of coding (temporal coding and “analog” coding) to delineate the molecular, biophysical, and circuit mechanisms that underlie neural coding and behavior. We have identified 2 neural circuits in Drosophila that allow for exquisite experimental control and where the impact of temporal pattern codes or analog codes on both target neuron physiology and animal behavior can be rigorously investigated. This study will contribute to the understanding of the fundamental principles that underlie how neural codes generate neurophysiological signals and behavior.