High BMI Linked to Weak Smell-Eating Circuit in Brain

Summary: A new study reveals a new brain circuit linking smell and eating behavior. The weaker the connection between these regions, the higher a person’s body mass index (BMI).

This finding suggests a potential neural mechanism underlying overeating, in which disrupted circuits may fail to signal satiety, leading to excessive food consumption.


  • A newly discovered brain connection links smell and eating behavior.
  • Weaker connections correlate with higher BMI, suggesting a role in overeating.
  • This discovery could pave the way for future treatments against obesity.

Source: Northwestern University

Why are some people easily able to stop eating when they are full and others not, which can lead to obesity?

A Northwestern Medicine study found that one reason could be a recently discovered structural connection between two brain regions that appears to be involved in regulating eating behavior. These regions involve smell and behavioral motivation.

Odors play an important role in guiding motivated behaviors such as food intake and, in turn, olfactory perception is modulated by our hunger. Credit: Neuroscience News

The weaker the connection between these two brain regions, the higher a person’s body mass index (BMI), report the Northwest scientists.

Investigators discovered this connection between the olfactory tubercle, an olfactory cortical region that is part of the brain’s reward system, and a region of the midbrain called the periaqueductal gray (PAG), involved in motivated behavior in response to negative feelings like pain and threat. potentially in power suppression.

The study will be published on May 16 in the Journal of Neuroscience.

Previous research conducted at Northwestern by co-author Thorsten Kahnt, now at the National Institutes of Health, showed that the smell of food is appetizing when you’re hungry. But the smell is less appealing when you eat this food until you are full.

Odors play an important role in guiding motivated behaviors such as food intake and, in turn, olfactory perception is modulated by our hunger.

Scientists haven’t fully understood the neural underpinnings of how smell contributes to how much we eat.

“The desire to eat is linked to the appeal of the smell of food – food smells better when you are hungry than when you are full,” said corresponding author Guangyu Zhou, research assistant professor of neurology at the Feinberg School of Medicine at Northwestern University.

“But if the brain circuits that help guide this behavior are disrupted, these signals can become confused, making eating gratifying even when you’re full. If this happens, a person’s BMI could increase. And that’s what we found. When the structural connection between these two brain regions is weaker, a person’s BMI is higher on average.

Although this study does not show it directly, the study authors hypothesize that healthy brain networks connecting reward areas to behavior areas could regulate eating behavior by sending messages telling the individual what to eat no longer does him any good when he is full. It actually hurts to eat too much. It’s like a switch in the brain that turns off the desire to eat.

But people whose circuits connecting these areas are weak or disrupted might not receive these stop signals and continue eating even when they aren’t hungry, the scientists explained.

“Understanding how these fundamental processes work in the brain is an important prerequisite for future work that may lead to treatments for overeating,” said lead author Christina Zelano, associate professor of neurology at Feinberg.

How the study was carried out

This study used MRI brain data from the Human Connectome Project, a large multicenter NIH project designed to create a network map of the human brain.

Northwestern’s Zhou found correlations with BMI in the circuit between the olfactory tubercle and the midbrain region, the periaqueductal gray. For the first time in humans, Zhou also mapped the strength of the circuit across the olfactory tubercle, then replicated those findings in a smaller MRI brain data set that the scientists collected in their lab at Northwestern.

“Future studies will be needed to uncover the exact mechanisms in the brain that regulate eating behavior,” Zelano said.

Funding: The research reported in this press release was supported by Grants R01-DC-016364, R01-DC-018539, R01-DC-015426 from the National Institute on Deafness and Other Communication Diseases and by the intramural research at the National Institute on Drug Abuse. ZIA DA000642, all National Institutes of Health.

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

About this research news in neuroscience, olfaction and obesity

Author: Marla Paul
Source: Northwestern University
Contact: Marla Paul – Northwestern University
Picture: Image is credited to Neuroscience News

Original research: Closed access.
“Structural connectivity between the olfactory tubercle and the ventrolateral periaqueductal gray involved in human feeding behavior” by Thorsten Kahnt et al. Journal of Neuroscience


Structural connectivity between the olfactory tubercle and the ventrolateral periaqueductal gray involved in human feeding behavior

The olfactory tubercle (TUB), also called the tubular striatum, receives direct input from the olfactory bulb and, along with the nucleus accumbens, is one of the two major components of the ventral striatum.

As a key part of the reward system, the ventral striatum is involved in feeding behavior, but the vast majority of research on this structure has focused on the nucleus accumbens, leaving the role of the TUB in feeding behavior understudied. .

Given the importance of olfaction in food seeking and consumption, olfactory input to the striatum should contribute significantly to motivated eating behavior. Yet, the TUB is very understudied in humans, with very little understanding of its structural organization and connectivity.

In this study, we analyzed macrostructural variations between the TUB and the whole brain, and explored the relationship between structural pathways of the TUB and eating behavior, using body mass index (BMI) as an indicator in women and men.

We identified a unique structural covariance between the TUB and the periaqueductal gray (PAG), which has recently been implicated in feeding suppression. We further show that white matter integrity between the two regions is negatively correlated with BMI.

Our results highlight the potential role of the TUB–PAG pathway in the regulation of feeding behavior in humans.

Statement of Significance

Growing evidence suggests that olfaction plays an important role in human eating behavior. However, the neural underpinnings of this role remain relatively unexplored.

Here, we examined the structural connectivity of the olfactory tubercle, involved in both olfaction and reward, using magnetic resonance imaging.

We found that unique connectivity of the olfactory tubercle with the periaqueductal gray correlated with body mass index.

Our results highlight the potential role of this pathway in the regulation of human feeding behavior.

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