New findings on binge eating

The sense of smell, not taste, regulates the feeling of satiety

Researchers from Charité have new findings on olfaction and satiation to report. In this section, study lead PD Dr. Friedrich Johenning answers questions about the research findings.

What was the research question or scientific inquiry behind your study?
We wanted to understand how the sense of smell influences feeding behavior—especially why mammals tend to consume more during fast or binge-like meals, even beyond homeostatic need. We hypothesized that the olfactory cortex, the brain region responsible for processing smells, plays an active role in this process. The underlying concept is sensory-specific satiation: conscious sensory experience of flavor can enhance and prolong the feeling of fullness.

How did you approach the topic?
We equipped mice with miniaturized microscopes that allowed us to observe brain activity in real time as the animals moved freely and ate. This enabled us to track how olfactory sensory representations in the brain changed depending on feeding speed. In addition, we used optogenetics to selectively switch the olfactory cortex on or off with light to test its causal role in feeding.

What did you discover?
During slow feeding, the olfactory cortex responds distinctly to different flavors with the activation of flavor specific neuronal ensembles. In contrast, during binge feeding, activity in this region is broadly suppressed, a phenomenon we did not observe in the taste sensing gustatory cortex. This suppression delays the onset of satiation—mice eat longer. When we optogenetically silenced the olfactory cortex during feeding, mice ate significantly more; when we activated it, they stopped eating sooner. This demonstrates that the olfactory cortex acts as a regulatory switch for sensory-driven satiation.

^{Schematic representation of activated neurons in the olfactory cortex during a live experiment using a miniature microscope, when mice eat slowly. The mice were offered nutritionally identical food with different flavors (strawberry and chocolate) as well as a sugar solution. We observed a clearly separated representation of neurons responding to strawberry flavor (blue), chocolate flavor (orange), and the sugar solution (green). During fast eating (“binge feeding”), these neurons are suppressed. © Neuron | Johenning}

Was there anything that surprised you?
We were especially surprised to discover that this suppression is not inherited from the olfactory sensory neurons, but is instead driven by an internal value system—specifically, inhibitory neurons in the olfactory tubercle, a reward-related brain region. This means that the more valuable the food, the more the olfactory cortex is “turned down” during fast feeding, thereby reducing sensory satiation.

What’s your takeaway?
Our results show that smell is not just passively involved in eating—it is actively regulated depending on how much we like the food and how quickly we eat. This may help explain why certain eating patterns and food types lead to overconsumption. In the long term, this insight could inform new strategies for treating eating disorders and obesity.

Source
Lo H et al. Feeding-induced olfactory cortex suppression reduces satiation. Neuron 2025 Aug 15. doi: 10.1016/j.neuron.2025.07.020

Contact:
PD Dr. Friedrich Johenning
Institute for Cell Biology and Neurobiology
Neuroscience Research Center
Charité – University Medicine Berlin

Links:
Link to the original article on the Cell Press website 

Link to the Charité website of the Johenning Lab (Sensory biology of feeding