New Olfactory Brain Circuit Links Food Smell to Feeling Full

Summary: Researchers have discovered a previously unrecognized neural pathway in mice that connects the sense of smell with an anticipatory feeling of fullness. In lean mice, exposure to food odors rapidly activates a specific group of nerve cells in the medial septum, signaling satiety and leading to reduced food intake. This response is impaired in obese mice, suggesting that obesity may disrupt olfactory-driven appetite control.

The study, led by a team at the Max Planck Institute for Metabolism Research, maps how odor information travels from the olfactory bulb to the medial septum and how this information influences feeding behavior. The findings point to a sensory mechanism that primes satiety at the very start of a meal and reveal important differences in how lean and obese animals respond to food-related smells.

Key Findings

• New fullness circuit: A direct neural route from the olfactory bulb to glutamatergic neurons in the medial septum (MSVGLUT2) reduces feeding in lean mice when they detect food odors.
• Obesity-related impairment: Diet-induced obese mice do not show this anticipatory satiety response, indicating disrupted olfactory signaling or altered medial septum activity in obesity.
• Possible human relevance: The same population of medial septum neurons exists in the human brain, raising the possibility that olfactory-based strategies could influence appetite regulation, though human responses remain to be tested.

Using whole-brain mapping and functional recordings, the researchers tracked which brain regions activate in response to food smells. They identified a distinct population of glutamatergic neurons in the medial septum that respond selectively to food odors but not to non-food scents. These neurons show a biphasic activity pattern: a rapid, transient activation when a food odor is first detected and a prolonged inhibition after ingestion begins. Because these medial septum neurons receive direct projections from the olfactory bulb, their activation occurs within seconds of detecting a food odor and can promptly influence feeding behavior.

Behavioral experiments showed that when the olfactory bulb-to-medial septum pathway was stimulated just before eating, lean mice reduced their food intake. This suggests that odor-driven activation of the circuit creates an anticipatory signal of fullness, shortening subsequent eating episodes. The authors propose that such a mechanism could be adaptive in wild animals by minimizing time spent exposed to predators while feeding.

How excess weight changes smell-driven appetite

In contrast to lean animals, mice with diet-induced obesity failed to activate the medial septum neurons in response to food odors, and stimulating the pathway did not reduce their food intake. Prior work has shown that obesity alters olfactory system function and neuronal activity in the olfactory bulb; this new result indicates that downstream circuits, including the medial septum, can also be affected. The disruption may help explain why some individuals with obesity are less responsive to sensory cues that normally curb eating.

While the medial septum cell population identified in mice is also present in humans, it remains unclear whether the same odor-responsive mechanism operates in people. Human studies have provided mixed evidence: certain odors can reduce appetite for some individuals, while others—particularly in people with overweight or obesity—may increase intake. Clarifying whether a comparable olfactory-to-medial-septum pathway exists and functions similarly in humans will be important before considering clinical applications.

The research highlights the importance of smell in the neural regulation of appetite and obesity. By showing that odor cues can prime satiety through a defined circuit, the study suggests new avenues for preventing overeating that take sensory perception into account. Any future interventions would need to consider that olfactory modulation appears effective in lean animals but may be compromised by obesity.

About this research

Author: Maren Berghoff
Source: Max Planck Institute for Metabolism Research
Contact: Maren Berghoff – Max Planck Institute
Image credit: Neuroscience News

Original research: A study led by Sophie Steculorum and colleagues published in Nature Metabolism reports on a food-sensitive olfactory circuit that drives anticipatory satiety. The research presents open-access data characterizing how olfactory inputs engage medial septum glutamatergic neurons and how this pathway modulates feeding differently in lean versus diet-induced obese mice.

Abstract (summary): Food-related sensory perception powerfully influences feeding circuits, yet the neuronal bases and behavioral consequences are incompletely understood. This study maps odor-driven brain activity and identifies medial septum glutamatergic neurons as key mediators of an anticipatory satiety signal in male mice. MSVGLUT2 neurons are activated transiently by food odors and are inhibited after ingestion. They receive direct olfactory bulb input, and activating the olfactory bulb→medial septum pathway before eating reduces feeding in lean mice but not in diet-induced obese mice. The findings uncover a sensory circuit that integrates olfactory food cues to prime satiety at the start of a meal.