Summary: New research reveals how neural circuits compute risk versus reward, showing that internal hunger state can reverse the direction of information flow in the nervous system to influence decision making.
Hunger flips the neural switch on risk-taking
The hungrier the animal, the more risk it will accept to obtain food. Researchers at Yale report that when an animal must weigh danger against a valuable reward, hunger can change how its nervous system processes information: higher-order brain centers send signals back to sensory pathways to implement decisions, rather than simply receiving sensory input.
Michael Nitabach, professor of cellular and molecular physiology and professor of genetics at Yale, and colleagues examined how this reversal of information flow allows an animal to choose whether to accept a threat to reach food. Their study, led by Yale graduate student D. Dipon Ghosh, used the roundworm Caenorhabditis elegans to probe the circuit-level mechanisms that underlie such risk-reward decisions.
In the experiments, worms faced a clear trade-off: cross a hyperosmotic barrier that risks desiccation, or avoid the barrier and forgo an attractive food odor on the other side. By comparing well-fed and food-deprived animals, the team identified the neural circuitry and modulatory signals that alter threat tolerance depending on hunger state.
Top-down signaling controls sensory sensitivity
Instead of only relaying sensory signals upward through a feedforward chain, the researchers found that a specific interneuron exerts a top-down influence on primary sensory neurons. This interneuron releases an extrasynaptic aminergic signal that potentiates osmosensory neurons, increasing their sensitivity to the barrier when food is available. When worms are food-deprived, this aminergic feedback is suppressed, lowering sensory sensitivity to threat and increasing willingness to cross the dangerous barrier.
In other words, internal physiological state—hunger—modulates a neural feedback pathway that effectively reverses the typical direction of information flow. The result is a circuit architecture that can bias behavior toward either avoidance or reward-seeking depending on need.
Broader implications
Although this work was performed in C. elegans, the authors point out that similar top-down modulatory signaling exists in mammals, including humans. The study therefore offers a plausible, testable mechanism by which internal states such as hunger could alter sensory processing and decision policies in other animals. By mapping the cellular players and demonstrating how modulation shifts network dynamics, the research provides a concrete example of how internal state and multisensory inputs are integrated to guide adaptive behavior.
Institution: Yale University
Press summary adapted from: Yale press materials
Original research article: “Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegans” by D. Dipon Ghosh, Tom Sanders, Soonwook Hong, Li Yan McCurdy, Daniel L. Chase, Netta Cohen, Michael R. Koelle, and Michael N. Nitabach. Published in Neuron, online November 17, 2016. doi:10.1016/j.neuron.2016.10.030
Abstract
Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegans
Highlights
• An autocrine neuropeptide signaling motif plays a role in regulating a C. elegans multisensory decision.
• The multisensory decision is modulated by a top-down, extrasynaptic aminergic signal.
• Computational modeling exposes neuronal network dynamics that underlie the decision process.
• Food deprivation suppresses the aminergic feedback pathway, increasing tolerance for threat.
Summary
Animals must often integrate multiple sensory cues in natural contexts to balance avoidance of danger with approach to valuable resources. How internal physiological state links to threat-reward decision making has been unclear. To address this, the authors presented C. elegans with the choice to cross a hyperosmotic barrier, which poses a desiccation threat, to reach an attractive food odor. They identified a specific interneuron that controls this decision via top-down extrasynaptic aminergic potentiation of primary osmosensory neurons, enhancing their sensitivity to the barrier. Food deprivation increases the worm’s willingness to cross the dangerous barrier by suppressing this potentiation pathway. These findings define a potentially general neural circuit motif for how internal state governs threat-reward decision making.
“Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegans” by D. Dipon Ghosh et al., Neuron, published online November 17, 2016. doi:10.1016/j.neuron.2016.10.030