The Power of Smell

The Power of Olfaction: Discoveries About Our Sense of Smell and Chemosensation

Dr. Noam Sobel is a neurobiology professor at the Wiseman Institute of Science who studies olfaction and chemosensation.
Humans have a sense of smell as good as dogs and are adept at sensing the chemical world around them.
Humans take chemicals from other people and apply them to their own body, processing information about that person's chemicals subconsciously to determine things like stress levels and hormone levels.
Tears from others can impact our hormone levels in powerful ways.
There is a regular alternation of ease through which we breathe through one nostril or the other, which reflects an underlying dynamic of our nervous system and affects our alertness or sleepiness.
Dr. Sobel's lab discovered that we are always sensing our own odors, even though we might not notice our own smell, and we periodically smell ourselves deliberately in order to change our cognition and behavior.
The olfactory epithelium is the sensory surface of the olfactory system, with about 6-7 million receptors in humans, and probably about 350 different types of olfactory receptor subtypes.
Odorants interact with receptors in the olfactory epithelium and undergo transduction to become a neural signal that propagates via the olfactory nerve to the olfactory bulb, the first target in the brain.
Many people lose their sense of smell due to trauma, with the more common cause being a contra coup injury to the back of the head that generates a shearing motion on the crib form plate and severs the olfactory nerve.
Olfaction also involves retronasal olfaction, where odorants come up through the back of our throat and out of our nose, and plays a big part in the contribution of olfaction to food and taste.
Humans have subconscious abilities related to olfaction, including pheromones, which impact our emotions, decision-making, and who we choose to relate to or not.
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Olfactory neurons in the epithelium can regenerate, but if they are completely lost, they may not find their way back to the bulb, resulting in permanent loss of smell.
Partial loss or regrowth of olfactory neurons can result in recovery of sense of smell, as they grow along the trajectory of other axons.
The rule of thumb for recovery of sense of smell after an injury is one to one and a half years, after which the chances of recovery decrease significantly.
Alpha lipoic acid, an over-the-counter remedy, has been shown to accelerate the recovery of sense of smell, but olfactory training is a more successful approach.
Olfactory training involves smelling different odors to keep olfactory neurons active and maintain their connections to avoid degeneration.
Olfactory neurons are the only neurons that systematically regenerate in the adult mammalian brain.
Every receptor subtype in the olfactory system is responsive to a small subset of molecular shapes, called odotopes, and all receptors of one subtype converge to one or two glomeruli in the olfactory bulb.
The olfactory system projects widely to several targets in the brain, including the primary olfactory cortex, amygdala, hypothalamus, and cerebellum.
Olfactory memories are formed more easily and maintained more robustly than other sensory memories, and the first exposure to a smell generates a particularly robust representation in the brain.
The olfactory system has a direct pathway to the hippocampus, one of the primary encoding centers for memory, which is a remarkably short pathway compared to other sensory systems.
Humans have a remarkable sense of smell, and humans can improve their ability to track scents quite robustly, especially if they are deprived of vision and somatic sensation.
Olfactory training can improve one's sense of smell, and people can learn to detect odors more effectively through practice, even if they have a poor sense of smell.The Incredible Ability of the Human Sense of Smell
Humans have a remarkable sense of smell, with a detection threshold of 0.2 parts per billion for certain odors.
The ability to detect and differentiate odors is linked to the structure and function of the olfactory epithelium and bulb in the nose, which sends signals to the brain for processing and interpretation.
Humans can track odors like dogs and have been shown to effectively follow a consistent odor path in the grass.
The ability to track odors is linked to the autonomic nervous system and the balance between the sympathetic and parasympathetic components.
The alternating left-right nostril periodicity called the "nasal cycle" reflects this balance, with the high flow nostril reflecting sympathetic dominance and the low flow nostril reflecting parasympathetic dominance.
The nasal cycle can be measured and is being studied as a potential disease marker, such as for ADHD.
The nasal cycle can be influenced by breathing techniques, such as those used in yoga, but no evidence suggests that individuals can willfully switch between nostrils without manual intervention.
Researchers are studying the direction of causality between the nasal cycle and the autonomic nervous system, with ongoing experiments to better understand the relationship.
The incredible sense of smell in humans can be used for practical purposes, such as adding odorants to cooking gas to detect gas leaks.
Humans can detect odors at incredibly low concentrations, such as estro tetra enol at 10 to the negative 12 molar in the liquid phase.
The human sense of smell is linked to brain function and can improve with training, such as in the ability to distinguish between similar odors.
Understanding the mechanics of the human sense of smell has practical applications for disease diagnosis and treatment, as well as potential for enhancing olfactory abilities in certain contexts.The Link Between Olfaction, Nasal Breathing, and Brain Function
Researchers are using a cold water hand exposure paradigm to study individual differences in pain tolerance.
The exposure to cold water generates a shift in the nasal balance, potentially driven by autonomic arousal.
The nasal cycle is a different story about brain function, not shaped by the olfactory system but rather timing and driving patterns of neural activity and cognitive processing.
Nasal inhalation is timing and driving many aspects and patterns of neural activity and cognitive processing, not just olfactory information.
A study showed that people performed significantly better on a visual spatial task on inhalation versus exhalation.
Nasal inhalation is great for health, dental health, and cognition. It shapes cognition and is modulating it.
The olfactory sensory neurons are at the tops of the nostrils and are part of the brain, and loss of the sense of smell is an early sign of neurodegeneration.
There are two standard clinical tests of olfaction: the UPSIT and Sniffin' Sticks. They are not as convenient as delivering stimuli in vision and audition.
Congenital anosmia, being born without the sense of smell, is diagnosed at an average age of 14 years old and is associated with shorter lifespan, reduced social and romantic contacts.
Congenital anosmia sufferers have noses and nostrils, and most of them don't have olfactory bulbs in adulthood.
There is a direct link between the olfactory system and some of the hypothalamic systems that regulate the release of gonadotropins.
Not all congenital anosmic individuals have Kallmann syndrome, a condition of hypogonadic development, but some do.