In elementary school, we learned about our five senses and their importance. We are grateful for these four senses because they all contribute to our survival and can provide our lives with so much depth and richness. The sense of smell, however, is the one that receives the least amount of praise from us of all the senses. This might be the case because much of it takes place in our subconscious in contrast to other senses. So, most individuals prefer to retain their sense of smell rather than lose access to technology.
Most people don’t realize it, but our sense of smell significantly enhances how we see the world. Different smells can alter your mood, take you back to an old memory, and perhaps even strengthen your relationship with loved ones. Your sense of smell significantly influences your health. If your sense of smell deteriorates, it may impact your physical health, daily safety, diet, and nutrition.
Additionally, Northwestern University researchers found that the secret to a healthy diet may lie in our ability to smell. The study results published in the journal PLOS Biology suggest that ingesting food also affects our perception of smell, which may influence what we eat next. According to imaging results from the study, the brain reacts to recent meal-like odors less “food-like” than it does to odors from other foods. The interaction between fragrance and food consumption might have helped humans evolve a more varied diet.
Given the close connection between olfaction and food intake, hunger and satiety may impact how we perceive odors. However, human research addressing this question heavily relies on subjective pleasantness ratings and threshold testing for single odorants. Previous studies have demonstrated that the subjective value of food odors decreases with food intake and that satiety and hormone variations that control appetite may influence olfactory sensitivity. It has not been investigated whether hunger and satiety affect olfactory perceptual judgment.
Therefore, the researchers of the PLOS study investigated how the sense of smell influences learning and appetite behavior, particularly as it relates to psychiatric conditions like obesity, addiction, and dementia. They did this using brain imaging, behavioral testing, and non-invasive brain stimulation. The team wanted to determine whether and how food intake affects our ability to sense food scents after discovering in a previous study that patients with sleep deprivation have changed brain responses to smell.
The team created a novel task for the study that involved exposing participants to a blend of a food fragrance and a non-food smell (either “pizza and pine” or “cinnamon bun and cedar” — odors that “pair well” and are distinct from each other). From pure food to pure non-food, the ratio of food and non-food odor altered in each blend. Participants were asked whether the non-food odor or the food odor predominated after introducing the mixture.
Inside an MRI scanner, participants completed the test twice: once when they were ravenous and once after consuming a meal that matched one of the two smells.
The team then calculated the amount of food odor that had to be present in the combination for each session for the participant to perceive it as predominating. The researchers discovered that when participants were hungry, they required a lower proportion of food odor to be present in a mixture for it to be perceived as dominant. For instance, a participant may need a mixture of 50% cinnamon buns to cedar when hungry but 80% full of cinnamon buns.
Participants in the study who had just consumed pizza or cinnamon rolls were less likely to detect “meal-matched” odors but not non-matched odors. Brain scans that revealed similar changes in brain activity in areas of the brain that process smells were used to further support the findings.
These results demonstrate that, in addition to scent controlling what we eat, food intake also controls our sense of smell. This feedback between food intake and the olfactory system may have evolutionary advantages.
The relationship between our nostrils, what we seek out, and what we can detect with our noses may still be quite essential, they continued, even though people don’t typically see the hunter-gatherer adaptation come out in daily decision-making. For instance, if the nose isn’t functioning properly, it may break the feedback loop, resulting in compulsive eating and obesity issues. Another connection to the olfactory system under study by scientists may be tied to sleep disruption.
In conclusion, the study’s behavioral findings show that olfactory perceptual decisions can be adaptably changed to suit the current motivational state. Additionally, the neurological data point to a plausible mechanism for this behavioral change involving odor-specific modulation of olfactory/limbic region brain activity.
Shanahan, L. K., Bhutani, S., & Kahnt, T. (2021). Olfactory perceptual decision-making is biased by Motivational State. PLOS Biology, 19(8). https://doi.org/10.1371/journal.pbio.3001374
