Behind Every Scent Lies a Two-Stage Brain Mystery

Understanding the sequential brain activity in decoding smell can provide a new pathway to treat smell disorders.

A team of researchers discovered a two-phase, timed process that is involved in odor perception by the brain. The distinct mechanism by olfactory neurons first recognizing the chemical structure of a smell, and then later detecting the pleasantness and unpleasantness of the scent.

The two-stage pattern of brain activity is called as “early objective coding” and “later subjective coding” with the latter being linked with person's memory and cultural context.()

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Your brain identifies what you smell in advance you realize it. The new insight of the #smell-process could transform diagnoses and treatments for #olfactory-dysfunction. #olfactorydisorders #neurobiology #olfaction #brainresearch #sense_of_smell

The study on brain cognition during odor perception was organized by scientists led by Masako Okamoto at the University of Tokyo. The outcomes were published in the journal JNeurosci.

Such profound understanding about how brain circuitry is involved in olfactory sensation could help recast diagnoses and therapies for olfactory disorders (OD). The precision of the later activity is correlated with a heightened awareness of odor pleasantness in daily life.

Decoding Olfaction: Early Identity, Late Pleasantness

When a person first sense any smell, the signals reach the olfactory bulb, a region underside of the forebrain and above the nasal cavity. The signals are then relayed by olfactory neurons to the parts of brain for smell perception, memory, and emotion.

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Scientists observed that these electrical signals are processed in two-level mechanism depending upon the odor's physiochemical properties.

The identification information is bridged by sustained electrical activity between the stage one and stage two smell process, which was observed from EEG (Electroencephalography) frequency bands in the brain recordings.

Understanding the Sense of Smell
Researchers have demonstrated that the representation of an odor evolves after the first breath, and that an olfactory retentivity persists at the central level.

The molecular figure is recognized (discrimination) in the phase of early objective smell decoding and the determination of scent's pleasantness (hedonic value) happened in the later subjective smell decoding.

Hedonic value is the rate of person's emotional satisfaction or pleasure derived from an experience.

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Opening Pathways for Enhanced Smell Function

Summing up their research, says Okamoto, “In the very early stage after odor onset, the brain primarily encodes objective molecular features of odors to support odor discrimination at the behavioral level, and only later does it begin to represent subjective perceptual attributes, such as pleasantness.”

The researchers suggest that the different kinds of brain activity they identified may serve as a way to assess olfactory disorders or inform new strategies for enhancing olfactory function.

Reference:

Behavioral Relevance of Early Neural Coding of Low-Level Odor Features in Humans - (https://www.jneurosci.org/content/early/2025/11/07/JNEUROSCI.0203-25.2025)

Source-Eurekalert