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Related Concept Videos

Physiology of Smell and Olfactory Pathway01:20

Physiology of Smell and Olfactory Pathway

Humans detect odors with the help of specialized cells located in the upper part of the nasal cavity, called olfactory receptor neurons (ORNs). ORNs possess hair-like structures called cilia, which are receptive to sensations from the inhaled air. When an odorant molecule binds to a specific receptor on the cell of the cilia, it leads to a series of events that ultimately cause the ORN to send electrical signals to the olfactory bulb in the brain through the olfactory nerves.
The olfactory...
Olfaction01:25

Olfaction

The sense of smell is achieved through the activities of the olfactory system. It starts when an airborne odorant enters the nasal cavity and reaches olfactory epithelium (OE). The OE is protected by a thin layer of mucus, which also serves the purpose of dissolving more complex compounds into simpler chemical odorants. The size of the OE and the density of sensory neurons varies among species; in humans, the OE is only about 9-10 cm2.
The olfactory receptors are embedded in the cilia of the...
Tactile and Chemical Senses01:27

Tactile and Chemical Senses

Tactile senses encompass touch, temperature, and pain, each mediated by specific receptors. Touch receptors detect mechanical energy or pressure against the skin. Sensory fibers from these receptors enter the spinal cord and relay information to the brain stem. Here, most fibers cross over to the opposite side of the brain. The touch information then moves to the thalamus, which projects a map of the body's surface onto the somatosensory areas of the parietal lobes in the cerebral cortex. This...
Olfactory Receptors: Location and Structure01:03

Olfactory Receptors: Location and Structure

The process of olfaction, also known as the sense of smell, is a sophisticated chemical response system. The specialized sensory neurons that facilitate this process, known as olfactory receptor neurons, are situated in an upper segment of the nasal cavity, known as the olfactory epithelium. Olfactory sensory neurons are bipolar, with their dendrites extending from the epithelium's apex into the mucus that lines the nasal cavity. Airborne molecules, when inhaled, traverse the olfactory...
Introduction to Special Senses01:26

Introduction to Special Senses

Sensory receptors play an integral part in comprehending our external and internal environments. They receive diverse stimuli, converting them into the nervous system's electrochemical signals. This conversion occurs as the stimulus alters the sensory neuron's cell membrane potential, instigating the generation of an action potential. This action potential is subsequently transmitted to the central nervous system (CNS), which integrates with other sensory data or higher cognitive functions.
Parallel Processing01:20

Parallel Processing

The brain processes sensory information rapidly due to parallel processing, which involves sending data across multiple neural pathways at the same time. This method allows the brain to manage various sensory qualities, such as shapes, colors, movements, and locations, all concurrently. For instance, when observing a forest landscape, the brain simultaneously processes the movement of leaves, the shapes of trees, the depth between them, and the various shades of green. This enables a quick and...

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Related Experiment Video

Updated: Jul 5, 2026

Constructing an Olfactometer for Rodent Olfactory Behavior Studies
08:36

Constructing an Olfactometer for Rodent Olfactory Behavior Studies

Published on: April 11, 2025

The human brain distinguishes between single odorants and binary mixtures.

Julie A Boyle1, Jelena Djordjevic, Mats J Olsson

  • 1Department of Psychology, McGill University, H3A 2T5 Montreal, QC, Canada. julie.boyle@mcgill.ca

Cerebral Cortex (New York, N.Y. : 1991)
|May 1, 2008
PubMed
Summary

The human brain processes single odors and binary odor mixtures differently, with distinct brain regions activating based on odor composition and impurity. The orbitofrontal cortex shows graded responses to impurity and acts as an on-off detector for mixtures.

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Combining a Breath-Synchronized Olfactometer with Brain Simulation to Study the Impact of Odors on Corticospinal Excitability and Effective Connectivity
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Real-time In Vitro Monitoring of Odorant Receptor Activation by an Odorant in the Vapor Phase
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Real-time In Vitro Monitoring of Odorant Receptor Activation by an Odorant in the Vapor Phase

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Constructing an Olfactometer for Rodent Olfactory Behavior Studies
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Combining a Breath-Synchronized Olfactometer with Brain Simulation to Study the Impact of Odors on Corticospinal Excitability and Effective Connectivity
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Real-time In Vitro Monitoring of Odorant Receptor Activation by an Odorant in the Vapor Phase
09:53

Real-time In Vitro Monitoring of Odorant Receptor Activation by an Odorant in the Vapor Phase

Published on: April 23, 2019

Area of Science:

  • Neuroscience
  • Olfactory processing
  • Human brain imaging

Background:

  • Rodent studies indicate differential cortical processing of single odors versus odor mixtures.
  • Understanding human olfactory perception requires investigating how the brain distinguishes between single odorants and complex mixtures.

Purpose of the Study:

  • To investigate if single odorants and binary odor mixtures activate distinct brain regions in humans.
  • To explore the neural correlates of odor mixture processing and impurity detection in the human brain.

Main Methods:

  • Positron emission tomography (PET) scans were utilized to analyze brain activity.
  • Participants were exposed to single odorants (pyridine, citral) and five binary mixtures with varying proportions.
  • Brain activation patterns were compared between single odorants and mixtures.

Main Results:

  • Binary odor mixtures and single odorants elicited differential activation in specific cortical regions, including the cingulate, parietal, superior frontal, and orbitofrontal cortices.
  • The lateral orbitofrontal cortex (OFC) exhibited increased activity correlating with increasing odorant impurity.
  • The anterior OFC showed activation for binary mixtures but deactivation for single odorants.

Conclusions:

  • Binary odor mixtures and their constituent components are processed distinctly by the human brain.
  • The lateral OFC demonstrates a graded response to odor mixture impurity.
  • The anterior OFC functions as an 'on-off' detector for binary odor mixtures.