Every time you inhale through your nose, your brain gets a wakeup signal — olfactory neurons phase-lock non-olfactory cognition to inhalation, making nasal breathing during focused work a genuine learning tool.
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Olfactory neurons are unique: they replenish throughout life, unlike neurons in the cortex or retina — and the completeness of smell recovery after concussion is a real clinical readout of brain healing.
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Humans actively perform chemical communication without knowing it: women's emotional tears measurably suppress testosterone and sexual-arousal brain areas in men, and we subconsciously rub handshake chemicals onto our own mucous membranes within seconds of meeting someone.
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Taste receptors exist to detect survival-critical chemicals — sweet signals energy, salty signals electrolytes, bitter and sour signal poisons, umami signals amino acids — and a possible sixth receptor for dietary fat is supported by emerging data.
Protocols
Concrete recipes — what, when, how much, and why
5 items
Nasal breathing during focused work to enhance alertness and learning
WhatKeep your mouth closed and breathe through your nose during any focused cognitive work — reading, studying, writing — that does not require speaking, eating, or drinking.
WhenWhenever doing focused intellectual work or any task where learning and retention matter.
DoseContinuous during the work session. Even a few minutes of nasal-only breathing will measurably increase alertness compared to mouth breathing.
For whomAnyone who wants to optimize focus, learning, or memory encoding — especially students, knowledge workers, and anyone doing deliberate practice.
WhyEach nasal inhalation phase-locks a brain-wide alertness signal via the olfactory system's primitive connection to the rest of the brain. Subjects restricted to nasal breathing in controlled trials learned better than those allowed to mouth-breathe.
CaveatsNasal breathing during exercise or speech is not always practical; this protocol is specifically for quiet focused-work windows.
The underlying mechanism is that olfactory neurons — the most ancient sensory neurons in the brain — project not just to smell-processing areas but to the amygdala and arousal systems. Inhalation through the nose activates these projections regardless of whether any odor is present, sending a 'sample the environment and pay attention' signal to the entire cortex. Exhalation produces a measurable dip in this arousal tone. Over a 30-minute study block, dozens of inhalation-phase alertness pulses accumulate into a meaningfully higher average arousal level than the same block done through the mouth.
Mechanism
Nasal inhalation activates olfactory bulb neurons which project to the amygdala and broadly to cortical arousal networks via noradrenergic and cholinergic pathways. The phase-locking of non-olfactory cognition to inhalation rhythm has been measured electrophysiologically in humans.
As we inhale, what this paper shows is that the level of alertness goes up in the brain... Inhaling is a cue for the rest of the brain to essentially pay attention to what's happening, not just to the odors.
10-15 sniff olfactory priming exercise to heighten smell and taste perception
WhatTake any odorant — an orange, coffee grounds, an essential oil — and perform 10 to 15 slow, deliberate nasal inhalations directed at it, followed by exhales. Then smell the same object again.
WhenBefore meals to heighten taste experience, before wine or coffee tasting, or as a general olfactory training exercise done daily.
Dose10-15 sniff cycles takes about 60-90 seconds. Noticeable enrichment of perceived smell is immediate.
For whomAnyone who wants to enrich sensory experience of food and drink, or who wants to actively train their olfactory system for health maintenance and neuroplasticity.
WhyRepeated inhalation of an odorant sensitizes and primes the olfactory receptor neurons to that odorant's chemical profile, sharpening discrimination. The heightened smell experience then carries over to taste because smell and taste are deeply integrated in flavor perception.
CaveatsUse pleasant, non-noxious odorants. Do not use this exercise with ammonia or other caustic substances — you can damage your olfactory epithelium.
Huberman frames this as one of the fastest trainable shifts in any sensory system: 'No other system that I am aware of in our body is as amenable to these kinds of behavioral training shifts and allow them to happen so quickly.' Because olfactory neurons continually replenish, repeated stimulation accelerates healthy turnover and creates a richer receptor representation for frequently encountered odorants. The exercise is also a practical proxy for olfactory system health — if you cannot notice a difference before and after the 15-sniff block, that is worth paying attention to as a possible signal of olfactory health decline.
Mechanism
Repeated olfactory receptor activation increases receptor-neuron sensitivity via short-term facilitation and may accelerate local neurogenesis of fresh sensory neurons. The rich percept after multiple sniffs is partly peripheral (receptor sensitization) and partly central (olfactory cortex pattern completion).
You just do the simple experiment of taking, for instance, an orange. You smell it. Do 10 or 15 inhales followed by exhales of course or just through the nose... and then smell it again and you'll notice that your perception of that smell, the kind of richness of that smell will be significantly increased.
Post-TBI olfactory training to gauge and accelerate brain recovery
WhatAfter a concussion or head injury, systematically expose yourself to a varied set of distinct odorants daily — ideally pleasant, varied scents — and track whether your ability to perceive and distinguish them is improving over weeks.
WhenAfter any concussion or traumatic brain injury, as part of the recovery monitoring and rehabilitation protocol.
DoseDaily sessions of 5-10 minutes with 4-6 distinct odorants. Track qualitative improvement week by week.
For whomAnyone who has suffered a concussion or repeated head impacts — athletes, military personnel, accident survivors.
WhyThe cribriform plate sheares olfactory neuron axons during head impact; those neurons then regenerate. The rate and completeness of smell recovery reflects the rate of neurological recovery more broadly. Active olfactory training accelerates neurogenesis in the replenishment process.
CaveatsSmell recovery is one readout among many — it does not replace assessment of balance, cognition, or sleep quality, and should not be used as the sole criterion for return-to-activity decisions.
Huberman cites the 2020 review 'Olfactory dysfunction in traumatic brain injury: the role of neurogenesis' by Marin et al. in Current Allergy and Asthma Reports: 'Olfactory functioning disturbances are common following traumatic brain injury, TBI, and can have a significant impact on the quality of life... post injury olfactory training has shown promise for beneficial effects.' The training works by repeatedly driving the olfactory receptor neurons to fire, which supports the neurogenesis cycle: dying neurons are replaced faster when the system is being actively used. The same logic applies to age-related olfactory decline — smell training in older adults has been shown to slow deterioration.
Mechanism
Active engagement with odorants stimulates olfactory sensory neuron firing, which sends trophic signals supporting the progenitor cell population responsible for continuous neuronal replenishment in the olfactory epithelium.
If you've had a head injury or repeated head injuries, that enhancing your sense of smell is one way by which you can create new neurons... by interacting with things that have an odor very closely and by essentially inhaling more, focusing on the inhale to wake up the brain.
Also said
“Olfactory functioning disturbances are common following traumatic brain injury, TBI, and can have a significant impact on the quality of life. Although there's no standard treatment for patients with the loss of smell... post injury olfactory training has shown promise for beneficial effects.”— The clinical evidence base for olfactory training as a TBI recovery tool.
Use peppermint scent for a safe, mild arousal boost
WhatSmell peppermint or minty scents — from peppermint oil, mint leaves, peppermint gum, or similar — to trigger a mild alertness and attention boost without the risks associated with ammonia smelling salts.
WhenWhen you need a quick cognitive uplift: before a meeting, after a long drive, to reset focus mid-afternoon.
DoseA few deliberate nasal inhalations of the mint source. Effect is rapid — onset within seconds.
For whomAnyone seeking a non-stimulant, non-ingested way to temporarily boost alertness. Especially useful for people who do not tolerate caffeine well or who want a mild, reversible arousal tool.
WhyPeppermint scent activates specific olfactory neurons that project to the amygdala and arousal circuits, producing an adrenaline-adjacent alerting response similar to (but less intense than) ammonia salts, a cold shower, or a sudden loud noise.
CaveatsDo not use real ammonia or industrial smelling salts without supervision — you can damage olfactory epithelium and potentially eyes. Peppermint is the safe everyday substitute.
Huberman's framing: 'The reason they wake you up is because they trigger specific olfactory neurons that communicate with the specific centers of the brain, namely the amygdala and associated neural circuitry and pathways that trigger alertness of the same sort that a cold shower or an ice bath or a sudden surprise or a stressful text message would evoke.' The adrenaline/epinephrine arousal response can be triggered by a near-infinite variety of stimuli — smell is simply one of the fastest and most accessible. Peppermint is well-studied in this context with peer-reviewed data on attention enhancement.
Mechanism
Menthol and related compounds in peppermint activate TRPM8 cold-sensitive receptors in olfactory mucosa and also engage specific olfactory receptor neurons projecting to the amygdala, releasing noradrenaline into arousal circuits.
Minty type scents, whether you like them or not, will increase attention, and they can create the same sort of arousal response, although not as intensely or as dramatically as ammonia salts can.
Deliberate daily exposure to diverse odorants to build and maintain olfactory acuity
WhatRoutinely and deliberately smell a variety of odorants — herbs, spices, essential oils, foods, coffee — with focused attention on the differences and nuances between them, rather than passive incidental smelling.
WhenDaily, integrated into existing routines: morning coffee preparation, cooking, time outdoors.
DoseEven 5 minutes of attentive, diverse olfactory engagement per day is sufficient to support olfactory neuron health and training.
For whomEveryone, and especially older adults concerned about cognitive aging, given that olfactory decline is an early biomarker of neurodegenerative conditions including Parkinson's and Alzheimer's.
WhyOlfactory neurons replenish throughout life and the replenishment rate is supported by active use. Social interactions and exposure to varied odorants are among the strongest drivers of olfactory neurogenesis. Olfactory acuity is a strong indicator of overall brain health.
Huberman notes: 'How well we can smell and taste things is actually a very strong indication of our brain health.' The neurogenesis angle is key: unlike cortical neurons, these neurons turn over throughout life, which means this is one of the few sensory systems where deliberate behavioral practice has a direct effect on neuron-count maintenance. The comparison class is visual acuity, which cannot be trained in the same direct way in adults. Exercise also appears to increase olfactory neurogenesis via blood flow, though the data are thinner than for behavioral odor exposure.
Mechanism
Diverse odorant exposure stimulates a broad set of olfactory receptor neuron subtypes. Active use creates demand for progenitor-cell differentiation into replacement neurons, maintaining the density and variety of functional receptor neurons in the epithelium.
How well we can smell and taste things is actually a very strong indication of our brain health... interacting a lot with odors, preferably positive odors, and sniffing more, inhaling more... it's grounded in real mechanistic biology of how the brain wakes up and responds to these chemicals.
What's new
Personal practice updates, fresh positions, predictions
5 items
Nasal inhalation phase-locks non-olfactory cognition — not just smell
Noam Sobel's group (originally UC Berkeley, then Weizmann Institute) published data showing that the act of inhaling through the nose wakes up the entire brain — not just olfactory circuits — and that alertness, attention, and memory encoding are measurably higher during inhalation than exhalation. A separate Journal of Neuroscience paper showed nasal-only breathers outlearn mouth breathers.
Why this matters: This reframes nasal breathing from a 'yoga thing' into a mechanistic cognitive tool: every inhale is a genuine brain-alertness pulse. Exhaling causes a measurable dip in learning ability.
Background
Sobel's lab studies the interface of olfaction and cognition. The finding emerged from basic olfactory neuroscience but the human non-olfactory cognition result surprised even the field.
The paper title Huberman cites is 'Human non-olfactory cognition phase locked with inhalation' published in Nature Human Behavior. The mechanism makes evolutionary sense: smell is the most ancient sense, and inhaling is the primal signal to the rest of the brain that you are sampling your environment and should pay attention. The implication for everyday life is that any focused work that doesn't require speaking or eating should be done with mouth closed, breathing through the nose. The brain's arousal architecture — involving adrenaline/epinephrine — can be triggered by the act of nasal inhalation itself, separate from what you are smelling.
As we inhale, what this paper shows is that the level of alertness goes up in the brain... human non-olfactory cognition phase locked with inhalation. What that means is that the act of inhaling itself wakes up the brain.
Also said
“There is a separate paper published in the journal of neuroscience that showed that indeed if subjects human subjects are restricted to breathing through their nose, they learn better than if they have the option of breathing through their mouth or a combination of their nose and mouth.”— Confirms the cognitive-performance consequence of nasal vs. mouth breathing in controlled experiments.
Women's emotional tears measurably suppress men's testosterone and sexual arousal
A study published roughly 10 years ago in Science showed that when men smelled women's sadness-evoked tears (vs. saline control), they had a significant reduction in testosterone and reduced activation in brain areas associated with sexual arousal — a concrete chemical communication effect requiring no conscious awareness.
Why this matters: Proves that human chemical communication is real and bidirectional, even without a classical pheromone system. A tear — not a synthetic molecule — reshapes another person's hormonal state.
Background
The Weizmann Institute group designed the study to collect authentic emotional tears (recruiting women with high propensity to cry at sad films) as opposed to irritant-induced tears, to isolate the emotional-chemical signal.
Huberman's framing of this finding is explicitly about underscore the broader principle: 'chemicals that are made by other individuals are powerfully modulating our internal state.' The tears study is his clearest example because the effect was measured objectively — testosterone levels and fMRI arousal areas — rather than self-report. The saline control design rules out expectation effects. The fact that only male subjects were tested in this study is a limitation the field is still working to fill (effects of male tears on women are an open area).
Men that smelled these tears that were evoked by sadness had a reduction in their testosterone levels that was significant. They also had a reduction in brain areas that were associated with sexual arousal.
Also said
“What they did is they had women and in this case it was only women for whatever reason cry and they collected their tears. Then those tears were smelled by male subjects or male subjects got what was essentially the control which was the saline.”— The controlled design — real emotional tears vs. saline — makes the testosterone-suppression result causally clean.
Handshake chemical marking: humans subconsciously transfer and self-sample chemicals within seconds of meeting
A Weizmann Institute study on first-meeting handshakes found that within a few seconds of shaking hands, people reliably touch their own eyes — placing the other person's skin chemicals onto their own mucous membrane. Both parties do it. It is subconscious chemical sampling of another individual's biological state.
Why this matters: Reveals a completely hidden layer of human social behavior: our bodies run a rapid chemical-evaluation protocol on every new person we meet, entirely below conscious awareness.
Background
The study observed naturally occurring behavior in paired strangers rather than using self-report, making the finding behaviorally robust.
Huberman's interpretation: 'You are marking other people when you shake their hand, and they are then taking your mark and rubbing it on themselves subconsciously.' The chemicals being sampled are thought to include volatile signals about hormone status, immune compatibility, and general biological identity. This ties to the broader principle that human beings have never stopped using chemical sensing for social evaluation — they have just lost conscious awareness of it. Knowing this, Huberman suggests you can actually watch for the eye-touch behavior in real time when observing people meeting for the first time.
What they observed was almost every time within just a few seconds of having shaken hands with this new individual, people will touch their eyes. They are taking chemicals from the skin contact and they are placing it on a mucosal membrane of some sort.
Also said
“You're marking other people when you shake their hand, and they are then taking your mark and rubbing it on themselves subconsciously. So we all do these kinds of behaviors.”— Huberman's interpretive framing that this is active chemical surveillance, not accidental touching.
Olfactory neurons are the only neurons in the brain that continuously replenish throughout life
Unlike cortical neurons, retinal neurons, or cerebellar neurons — which do not regenerate once lost — olfactory sensory neurons in the nose turn over constantly throughout the lifespan. They die and are replaced by new ones, making olfaction the most trainable and neuroplastic sensory system in the adult brain.
Why this matters: Opens the olfactory system as a practical entry point for brain health maintenance and measurement — and as a uniquely regenerative system that can be deliberately improved at any age through exposure and training.
The mechanism of replenishment means that 'regeneration' (regrowth after damage) and 'replenishment' (normal turnover) are both occurring. In traumatic brain injury, the cribriform plate — a Swiss cheese-like bony structure through which olfactory neuron projections pass — can shear those processes off during a head impact. The neurons eventually regrow, and the completeness and speed of smell recovery after TBI is a clinical gauge of neurological recovery more broadly. Huberman cites the 2020 paper 'Olfactory dysfunction in traumatic brain injury: the role of neurogenesis' (Marin et al., Current Allergy and Asthma Reports) and notes that post-injury olfactory training has shown promise in accelerating recovery.
These olfactory neurons are really unique among other brain neurons because they get replenished throughout life. They don't just regenerate, but they get replenished... neurons in your cortex, in your retina, in your cerebellum, they do not do this.
Also said
“Olfactory functioning disturbances are common following traumatic brain injury, TBI, and can have a significant impact on the quality of life... post injury olfactory training has shown promise for beneficial effects.”— Clinical translation: active smell training post-TBI accelerates the neuronal replenishment that can restore function.
The taste-receptor map taught in schools is completely wrong — all five receptors are intermixed across the tongue
The high school textbook diagram showing sweet at the tip, bitter at the back, and sour on the sides is fiction. Sweet, salty, bitter, umami, and sour receptors are completely intermixed along the entire tongue surface, and a possible sixth receptor for dietary fat is now supported by data.
Why this matters: Corrects a persistent myth while revealing the deeper logic: each taste type signals a specific survival-relevant chemical class — not a flavor preference — and the fat receptor would explain why high-fat foods are so compelling even when we cannot taste fat directly.
Each of the five confirmed taste modalities maps to a specific chemical-survival function: sweet detects rapid energy (glucose); salty detects electrolytes; bitter detects potential poisons and hard-wires a gag reflex via a labeled-line projection to the brainstem; umami detects amino acids (protein presence); sour detects fermentation/spoilage. The gustatory nerve from the tongue travels to the nucleus of the solitary tract, then the thalamus, then insular cortex — where the conscious experience of taste is assembled. Fat, if confirmed as a sixth modality, would round out the macronutrient-sensing picture because fat is essential for nervous system function and all cell membranes.
It is a total myth, complete fiction that different parts of your tongue harbor different taste receptors... They are completely intermixed along your tongue.
Also said
“There are now data to support the idea, although there's still more work that needs to be done, that we also have receptors on our tongue that sense fat and that because fat is so vital for the function of our nervous system and the other organs of our body that we are sensing the fat content in food.”— The sixth-receptor hypothesis: dietary fat sensing would complete the macronutrient-detection picture.
Recommendations
Products, supplements, and tools mentioned in the episode
4 items
Nasal breathing during focused work sessions
Practice
Huberman's core behavioral recommendation from this episode: keep the mouth closed and breathe nasally during any cognitive work where speaking is not required.
Grounded directly in Sobel's Nature Human Behavior paper ('human non-olfactory cognition phase locked with inhalation') and the Journal of Neuroscience nasal-vs-mouth-breathing learning experiment. Huberman frames it as one of the most mechanistically well-supported free tools for cognitive performance.
You could imagine, and I think this would be beneficial for most people, to focus on nasal breathing while doing any kind of focused work that doesn't require that you speak or eat or ingest something.
Peppermint scent for alertness (over ammonia smelling salts)
Practice
Huberman recommends peppermint-based scents as the safe everyday arousal tool, explicitly discouraging unsupervised ammonia smelling salt use because of olfactory-epithelium and eye-surface damage risk.
Smelling salts (ammonia) are mentioned as having 'excellent peer-reviewed data' for effectiveness but are flagged as dangerous to use without supervision — ammonia proximity can damage olfactory pathways and even vision by irritating mucous membranes. Peppermint provides a safer version of the same amygdala-arousal mechanism.
vs alternatives
Ammonia smelling salts are more potent but carry real risk of olfactory epithelium damage and eye irritation. Peppermint gives a milder, safe version of the same adrenaline-mediated alerting pathway.
I'm not recommending that you do this necessarily, but there are excellent peer-reviewed data showing that indeed if you use smelling salts... they work because they trigger the fear and kind of overall arousal systems of the brain. This is why I think most people probably shouldn't use ammonia or smelling salts to try and wake up.
Olfactory training protocol (diverse odorant exposure) for brain health and TBI recovery
Tool
Huberman recommends deliberate, varied olfactory engagement as a tool for general brain health maintenance and as a specific intervention in TBI recovery, citing Marin et al. (2020) in Current Allergy and Asthma Reports.
The underlying logic: olfactory neurons uniquely replenish throughout life, and active use drives that replenishment faster. In healthy individuals, this maintains the density and variety of receptor neurons, preserving acuity. After TBI, it accelerates regeneration of sheared axon projections. The practice costs nothing and has no known downsides with safe odorants.
If you've had a head injury or repeated head injuries, that enhancing your sense of smell is one way by which you can create new neurons. And now you know how to enhance your sense of smell by interacting with things that have an odor very closely and by essentially inhaling more.
Marin et al. (2020) — Olfactory dysfunction in traumatic brain injury: the role of neurogenesis — Current Allergy and Asthma Reports
Book
Peer-reviewed review article Huberman reads directly from during the episode as the evidentiary basis for post-TBI olfactory training. He calls it 'quite good' and recommends it for anyone who has suffered head injuries.
I'd like to refer you to a really nice paper which is entitled olfactory dysfunction in traumatic brain injury the role of neurogenesis. The first author is Marin M I N. The paper was published in current allergy and asthma report. This is 2020. I spent some time with this paper. It's quite good.
Lines worth pulling out — contrarian, specific, or perfectly phrased
5 items
As we inhale, what this paper shows is that the level of alertness goes up in the brain... the act of inhaling itself wakes up the brain. It's not about what you're perceiving or what you're smelling.
The cleanest statement of the nasal-breathing-as-cognitive-tool principle: effect is mechanical, not olfactory.
Men that smelled these tears that were evoked by sadness had a reduction in their testosterone levels that was significant. They also had a reduction in brain areas that were associated with sexual arousal.
The most striking single finding in the episode — a tear reshapes another person's hormonal profile, proving human chemical communication is real and measurable.
It is a total myth, complete fiction that different parts of your tongue harbor different taste receptors. They are completely intermixed along your tongue.
Directly corrects a decades-old textbook error that persists in public understanding.
You're marking other people when you shake their hand, and they are then taking your mark and rubbing it on themselves subconsciously. So we all do these kinds of behaviors.
The handshake-chemical-transfer finding reframes an everyday social ritual as covert biological surveillance.
These olfactory neurons are really unique among other brain neurons because they get replenished throughout life. They don't just regenerate, but they get replenished... neurons in your cortex, in your retina, in your cerebellum, they do not do this.
Establishes the olfactory system as uniquely plastic and trainable in adulthood — and makes smell training a legitimate brain-health tool.
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Educational summary of the cited expert source — not medical advice. Open the source recording linked above and consult a qualified physician before acting on any protocol.
