A new study shows that the annoyance of odors is processed faster than the perceived quality

A specially created scent delivery device, along with machine learning-based analysis of the electroencephalogram recorded on the scalp, allowed University of Tokyo researchers to see when and where scents are processed in the brain. The study found that odor information in the brain was unrelated to perception during the early stages of processing, but when perception occurred later, unpleasant odors were processed faster than pleasant odors. . Problems with odor perception can be an early symptom of neurodegenerative diseases, so uncovering more of the neural bases of odor perception could help better understand these diseases in the future.

Does the smell of a hot cup of coffee help you start your day off right? Or can’t stand the loud and heady stuff? According to new research, how quickly your brain processes the smell of your morning drink may depend on whether you think that smell is pleasant or not.

A team from the University of Tokyo has created a special device capable of delivering 10 different smells precisely and quickly. The odors were administered to participants who rated their agreeableness while wearing noninvasive scalp-recorded electroencephalogram (EEG) caps, which record signals inside the brain. The team was then able to process the EEG data using machine learning-based computational analysis, to see when and where the range of odors was processed in the brain with high temporal resolution for the first time. time.

“We were surprised to be able to detect signals of odors presented from very early EEG responses, as quickly as 100 milliseconds after odor onset, suggesting that the representation of odor information in the brain happens quickly,” said PhD student Mugihiko Kato of the Graduate School of Agriculture and Life Sciences at the University of Tokyo.

The brain’s detection of the smell occurred before the smell was consciously perceived by the participant, which did not happen until several hundred milliseconds later. “Our study showed that different aspects of perception, particularly pleasantness, unpleasantness, and odor quality, emerged through different spatial and temporal cortical processing,” Kato said.

“The representation of unpleasantness in the brain emerged earlier than pleasantness and perceived quality,” said project associate professor Masako Okamoto, also from the Graduate School of Agricultural and Life Sciences. When unpleasant odors (such as rotten and rancid odors) were administered, participants’ brains could differentiate them from neutral or pleasant odors as early as 300 milliseconds after they appeared. However, the representation of pleasant odors (such as floral and fruity smells) in the brain did not occur until 500 milliseconds, around the same time that odor quality was also represented. 600 to 850 milliseconds after the onset of the odor, important areas of the brain involved in emotional, semantic (language) and memory processing then became most involved.

The early perception of unpleasant odors can be an early warning system against potential dangers. “How each sensory system recruits the central nervous system differs across sensory modalities (smell, light, sound, taste, pressure, and temperature). Elucidating when and where in the brain olfactory (smell) perception emerges helps us understand how the olfactory system works,” Okamoto said. “We also believe our study has broader methodological implications. For example, it was not known that EEG recorded from the scalp would allow us to assess odor representation from periods as early as 100 milliseconds.”

This high temporal resolution imaging of how our brain processes odors may be a stepping stone to a better understanding of the mechanisms of neurodegenerative diseases in the future, such as Parkinson’s and Alzheimer’s diseases, in which dysfunction of the Smell is an early warning sign. The team is interested in exploring several other avenues of research. “In our daily life, smells are perceived along with other sensory information like vision, and each sense influences the perception of the other,” Kato said. “Although we only presented olfactory stimuli in the current study, we believe it is important to analyze brain activity under more natural conditions, such as presenting odors with film.” Maybe Smell-O-Vision could still make a comeback?


This work was supported by the Grant-in-Aid for Scientific Research on Innovative Areas from Japan Society for the Promotion of Science to MO (18H04998 and 21H05808) and JST-Mirai program to KT (JPMJMI17DC and JPMJMI19D1).

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Materials provided by University of Tokyo. Note: Content may be edited for style and length.

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