What is hunger, and how does it guide behavior?

To answer this, and other related questions, at the level of both neurobiological mechanisms and psychological constructs, we are utilizing neuron-specific recombinase driver mice in conjunction with recombinase-dependent AAVs expressing various genetically encoded “tools” to selectively (in a neuron cell type-specific fashion): a) map connectivity between neurons to establish their “wiring diagrams”, b) manipulate neuron firing rates in vivo to determine their roles in regulating behavior and physiology, and c) measure neuron activity in vivo to establish their responses to discrete behavioral and physiologic perturbations. Specific approaches utilized include, electrophysiology, optogenetics, chemogenetics, rabies mapping, ChR2-assisted circuit mapping, in vivo assessments of neuronal activity, and single neuron transcriptomics. Such efforts are discovering the neural circuits that control hunger and the mechanisms by which “hunger” guides behavior, and also the ways in which the brain controls other related homeostatic drives, the autonomic nervous system and the neuroendocrine system. For more information, see the following review: Lowell BB, New Neuroscience of Homeostasis and Drives for Food, Water, and Salt. N Engl J Med 380: 459-471, 2019.