HoldsUp

Huberman Lab · 2025-11-10 · Andrew Huberman (host), Jennifer Groh

How Your Thoughts Are Built & How You Can Shape Them | Dr. Jennifer Groh

51 research-tied claims examined: 3 contradicted 2 overstated 1 context 37 supported 8 unverified

37 Supported by research
0:05:00Jennifer Grohsupportedvery low

The superior colliculus is responsive to both visual and auditory stimuli, and its auditory receptive fields shift depending on eye position.

"there's a brain structure called the superior colliculus that's responsive to both visual and auditory stimuli, and that the responses to auditory stimuli depended on where the eyes were looking. If you move the eyes, the neurons' receptive field, the region in space where they were responsive to, would shift as the eyes moved." (said at 0:05:00)

Extensive neurophysiological research in non-human primates and cats demonstrates that the superior colliculus integrates both visual and auditory information, and that the spatial location of auditory receptive fields in collicular neurons shifts according to orbital eye position to maintain alignment across sensory coordinates.

0:15:18Jennifer Grohsupportedhigh

The maximum interaural time difference for sound localization in humans is approximately half a millisecond.

"And it's something like about a half a millisecond is the largest delay you can experience." (said at 0:15:18)

The speaker claimed that the largest delay (interaural time difference, ITD) experienced for sound localization in humans is approximately half a millisecond. In human auditory acoustics and spatial hearing, the maximum physiologically possible ITD across an average human head (for sounds arriving at 90 degrees azimuth) is roughly 0.6 to 0.7 milliseconds (600–700 microseconds), which is well approximated as 'about a half a millisecond' (0.5 ms). Studies investigating auditory localization and natural ITD limits demonstrate that natural acoustic delays across the human head fall within this range.

0:20:50Jennifer Grohsupportedhigh

The physical folds of the outer ear filter incoming sounds and alter their frequency content to aid in sound localization.

"But actually the ear has these little folds in them and the folds filter the sound as it comes in. And in particular, it alters the frequency content of the sound." (said at 0:20:50)

The physical structure and folds of the outer ear (pinna) cause direction-dependent acoustic filtering, modifying the frequency spectrum of incoming sounds (creating direction-specific spectral notches and peaks, particularly at high frequencies above 4–8 kHz). The auditory system interprets these spectral cues to determine the elevation and front-versus-back location of sound sources in the vertical/sagittal planes.

0:24:10Jennifer Grohsupportedmoderate

The brain has an active mechanism that attenuates auditory transduction immediately before vocalization so individuals do not experience their own voice as overly loud.

"Number two, your brain has an active mechanism for manipulating the transduction of sound in your ears. That is to say, the conversion of sound into a neural signal that's going to go into the brain. So, your brain actually controls that process. And there's some thinking that it's, you know, turning down the volume just before you speak so that you don't get blasted by the sound of your own voice." (said at 0:24:10)

The brain possesses descending auditory efferent pathways, primarily the medial olivocochlear (MOC) efferent system and middle ear muscle reflexes, that modulate outer hair cell motility and cochlear micromechanics, thereby directly controlling the transduction of sound into neural signals at the level of the ear. Research demonstrates that this efferent system can activate phasically and synkinetically just prior to and during vocalization to damp cochlear resonance and attenuate peripheral auditory sensitivity to self-emitted sounds.

0:26:52Andrew Huberman (host)supportedhigh

Hearing loss is correlated with an increased risk of dementia.

"we now know hearing loss is correlated with dementia." (said at 0:26:52)

Extensive meta-analytic evidence from large prospective cohort studies consistently demonstrates that adult-onset hearing loss is correlated with a significantly increased risk of incident dementia and Alzheimer's disease (typical hazard ratios between 1.30 and 1.35), with evidence of a dose-response relationship per 10-decibel worsening in hearing ability.

0:23:05Jennifer Grohsupportedmoderate

An infant's head is approximately half the width of an adult's head, resulting in a maximum interaural time difference of approximately 0.25 milliseconds.

"a baby's head is about half the width of an adult's head. So that means that half millisecond for me is a quarter of a millisecond for a baby and it's going to change as they grow." (said at 0:23:05)

The speaker's statement accurately illustrates the relationship between head dimensions and acoustic interaural time differences (ITDs) across human development. In adults, the maximum ITD across the ears is roughly 0.5 to 0.7 milliseconds (500–700 µs). Because an infant's head dimensions are substantially smaller than an adult's (with newborn biparietal width and head circumference being approximately half to two-thirds of adult values), the maximum ITD experienced by an infant is correspondingly smaller (around 0.25–0.4 ms), meaning spatial auditory cues dynamically change as the head grows.

0:15:48Andrew Huberman (host)supportedhigh

The duration of a typical neuronal action potential is greater than 0.5 milliseconds.

"half a millisecond is less than the duration of a single action potential, right?" (said at 0:15:48)

Standard neurophysiology establishes that typical mammalian neuronal action potentials have a duration of approximately 1 to 2 milliseconds (and longer in certain cell types such as unmyelinated nociceptors or cardiac cells), meaning 0.5 milliseconds is indeed less than the duration of a typical action potential.

0:40:45Jennifer Grohsupportedhigh

Lower sound frequencies bend around objects more easily than higher frequencies.

"One is that the lower frequencies bend more bend more easily. So they they can go around these objects better." (said at 0:40:45)

The claim is supported by fundamental acoustic principles and wave physics. Diffraction occurs when sound waves encounter obstacles or openings; because lower frequencies have longer wavelengths relative to obstacle dimensions, they undergo greater diffraction (bending) around objects compared to higher frequencies (which have shorter wavelengths and tend to be cast in acoustic shadow / behave more like rays). This frequency-dependent attenuation and bending around obstacles is modeled in acoustic physics using low-pass behavior (where higher frequencies are attenuated more strongly in the diffraction shadow zone than lower frequencies).

0:41:05Jennifer Grohsupportedhigh

Humans tend to lose high-frequency hearing before they lose low-frequency hearing.

"Another thing that's wrapped up here is that we tend to lose high-frequency hearing before we lose low-frequency hearing." (said at 0:41:05)

The speaker's statement accurately reflects well-established auditory physiology and epidemiology. Age-related hearing loss (presbycusis) is universally characterized by progressive sensorineural hearing loss that begins at higher frequencies before progressing to affect middle and lower frequencies over time.

0:42:28Andrew Huberman (host)supportedhigh

Most red-green colorblind individuals are male due to the location of the gene mutation on the X chromosome.

"most red-green colorblind people tend to be males just because of where the the gene mutation is in the in the genome" (said at 0:42:28)

The claim is fully supported by established genetics and epidemiological data. Red-green color vision deficiency is an X-linked recessive trait caused by mutations, deletions, or rearrangements in the OPN1LW (red) and OPN1MW (green) opsin pigment gene cluster located on the X chromosome (Xq28). Because males have a single X chromosome (hemizygous), a single mutated copy causes the condition, resulting in a prevalence of roughly 7–8% in males compared to approximately 0.4–0.5% in females (who require mutations on both X chromosomes).

0:45:07Andrew Huberman (host)supportedmoderate

Magnesium threonate, theanine, chamomile extract, and glycine are clinically supported ingredients that help with falling and staying asleep.

"things like magnesium threonate, theanine, chamomile extract, and glycine along with lesser-known things like saffron and valerian root. These are all clinically supported ingredients that can help you fall asleep, stay asleep, and wake up feeling more refreshed." (said at 0:45:07)

Clinical trials and systematic reviews support that ingredients such as L-theanine, magnesium L-threonate, glycine, and chamomile have evidence supporting improvements in sleep latency, sleep quality, sleep architecture (such as deep and REM stages), and feelings of refreshment upon waking. Meta-analyses of L-theanine demonstrate statistically significant reductions in subjective sleep onset latency and daytime dysfunction, while randomized trials of magnesium L-threonate show improvements in sleep scores and daytime alertness.

0:46:19Andrew Huberman (host)supportedmoderate

PFAS chemicals are linked to health issues including hormone disruption, gut microbiome disruption, and fertility issues.

"these PFAS or forever chemicals like Teflon have been linked to major health issues such as hormone disruption, gut microbiome disruption, fertility issues, and many other health problems." (said at 0:46:19)

Per- and polyfluoroalkyl substances (PFAS) are well-documented endocrine-disrupting chemicals (EDCs). Systematic reviews of human epidemiological studies consistently demonstrate associations between PFAS exposure and hormone disruption (including altered levels of estradiol, luteinizing hormone, follicle-stimulating hormone, and thyroid hormones) as well as adverse fertility outcomes (such as increased time to pregnancy, reduced fecundability, earlier menopause, and altered semen quality). In addition, clinical and scoping reviews of human and experimental studies demonstrate that PFAS exposure is linked to gut microbiome dysbiosis, including shifts in alpha/beta diversity, alterations in specific bacterial taxa, and disrupted microbial metabolic pathways.

0:42:05Jennifer Grohsupportedmoderate

Every human culture has rhythm as a core component of its music.

"There is some variation as to whether or not, um, a culture embraces melody, embraces harmony, but every culture has rhythm." (said at 0:42:05)

Cross-cultural ethnomusicological and cognitive research supports the claim that rhythm is a core, universal feature of music across human cultures. A global empirical analysis of music across nine geographic regions (Savage et al., 2015) identified robust statistical universals spanning rhythmic features, metric structure, and percussion. While comparative musicologists distinguish between 'statistical universals' (features prevalent across all cultural traditions above chance) and absolute absence of counterexamples in every individual song, rhythm is universally present across all documented human musical cultures.

0:37:31Andrew Huberman (host)supportedmoderate

Long-wavelength light can pass through the human body and improve mitochondrial health.

"there are certain wavelengths of light that can pass through our body like long wavelength light. That's relatively new findings. I think it's really interesting and it's very healthy for us. Turns out, you know, mitochondrial health, etc." (said at 0:37:31)

The speaker's assertion is supported by research in photobiomodulation (low-level light therapy). Longer wavelengths of light, specifically in the red and near-infrared (NIR) optical window (~600–1100 nm), penetrate human soft tissue, bone, and neural parenchyma far deeper than shorter wavelengths (such as UV or visible blue/green light). Within cells, this light is absorbed by mitochondrial chromophores, particularly cytochrome c oxidase (complex IV of the mitochondrial respiratory chain), which stimulates ATP synthesis, modulates reactive oxygen species, releases nitric oxide, and enhances mitochondrial and cellular metabolism.

0:37:59Andrew Huberman (host)supportedhigh

Humans are biologically poised to detect interaural arrival time differences of half a millisecond between the two ears.

"Even though we are biologically poised to detect half-a-millisecond differences in the arrival time of the two ears, there are much greater differences in the arrival time of my voice bouncing off the table versus the walls versus the ceiling versus direct path." (said at 0:37:59)

Human binaural hearing relies heavily on interaural time differences (ITDs) for sound localization and spatial perception. The human auditory brainstem (notably the medial superior olive) possesses specialized neural circuitry that resolves arrival time disparities with microsecond precision (typically detecting differences as small as 10 to 50 microseconds), easily enabling detection and spatial processing of half-millisecond (500 microsecond) differences between the two ears.

0:39:08Andrew Huberman (host)supportedhigh

Liver pain can refer to the shoulder because of branching nerve pathways.

"Like someone with a with like liver pain will register that in their shoulder, you know, and and we think, oh, this is crazy. You know, it's not crazy that there's actually branches that that support that referred pain." (said at 0:39:08)

The speaker's claim is supported. Hepatic irritation or pathology (such as liver metastases, subcapsular hematomas, or post-ablation irritation) commonly refers pain to the right shoulder. Anatomically, sensory afferents from the hepatic capsule, falciform ligament, and overlying diaphragmatic peritoneum travel via branches of the phrenic nerve to the C3–C5 spinal cord segments. Because supraclavicular cutaneous nerves also originate from C3–C4 to supply sensation to the shoulder tip, convergence of these neural pathways causes visceral liver pain to be perceived in the shoulder.

0:42:56Andrew Huberman (host)supportedmoderate

Dogs perceive colors similarly to red-green colorblind humans, seeing red and green as brownish-orange.

"Red and green look kind of more orangish-burnt brown orange color, and dogs see the world that way all the time" (said at 0:42:56)

Canine retinas have dichromatic color vision based on two cone photoreceptor classes (short-wavelength and a single long/medium-wavelength cone), functioning similarly to human red-green color blindness (protanopia/deuteranopia). Behavioral testing using modified Ishihara tests confirms that dogs distinguish colors along a blue-yellow axis and cannot discriminate red and green hues, perceiving them similarly in brownish/yellowish tones.

1:03:44Jennifer Grohsupportedvery low

Auditory signals in the superior colliculus are modulated by eye position at the time a sound is presented.

"So this was auditory signals in the superior colliculus being affected by the position of the eyes at the time the sound was presented." (said at 1:03:44)

Electrophysiological studies in non-human primates and cats demonstrate that auditory responses and receptive fields of neurons in the superior colliculus are modulated by initial eye position in the orbit when an acoustic stimulus is delivered. This coordinate transformation aligns auditory representations with retinotopic visual and oculomotor maps. Because the evidence consists of neurophysiological experiments in animals, the GRADE certainty is rated very low under human GRADE guidelines.

1:04:10Jennifer Grohsupportedhigh

Visual localization is computed in eye-centered (retinotopic) coordinates, whereas auditory localization cues are computed in head-centered coordinates.

"light hits a particular, uh, location on the retina, and that retinal location tells us what the location of the visual stimulus is. But it tells us the location of the visual stimulus with respect to the direction the eyes are pointing. But our sound localization cues are with respect to, um—where's the sound with respect to the head." (said at 1:04:10)

The speaker's statement is textbook neurobiology and fully supported by sensory physiology. In vision, initial spatial localization is retinotopic/eye-centered because it is determined by where light strikes photoreceptors on the retina (relative to the direction of gaze). In audition, spatial localization cues (interaural time differences, interaural level differences, and spectral filtering by the head and pinnae) are fundamentally defined relative to the position and orientation of the ears on the head (head-centered coordinates).

1:05:35Jennifer Grohsupportedvery low

Eye movements modulate auditory neural signals across early auditory pathway structures outside the superior colliculus.

"And what we found was that in each of these areas, eye movements affect the auditory signals there too, even though they weren't in this convergent structure of the superior colliculus." (said at 1:05:35)

Electrophysiological recordings in non-human primates by Groh and colleagues demonstrated that eye position and eye movement-related signals modulate auditory responses in auditory pathway structures outside the classical multisensory superior colliculus, including the inferior colliculus (IC) and primary/belt auditory cortex (A1 and CM). As this evidence is derived from animal neurophysiology studies, GRADE certainty is very low.

1:06:20Jennifer Grohsupportedhigh

The middle ear contains two muscles that control the ossicles, and cochlear outer hair cells mechanically expand and contract.

"There are two muscles that control the bones of the middle ear. Uh, and then inside the cochlea, there are, uh, cells called outer hair cells that can actually expand and contract just the way a little muscle could." (said at 1:06:20)

The middle ear contains two muscles attached to the auditory ossicles: the tensor tympani (attached to the malleus) and the stapedius (attached to the stapes), which modulate sound transmission and protect the inner ear. Within the organ of Corti in the cochlea, outer hair cells (OHCs) exhibit somatic electromotility—rapidly elongating (expanding) and shortening (contracting) in response to membrane potential changes driven by the motor protein prestin to amplify mechanical vibrations.

1:08:25Jennifer Grohsupportedhigh

Otoacoustic emissions are sounds generated within the ear that can be measured using a microphone in the ear canal.

"you can put a microphone in the ear and you can measure things called otoacoustic emissions." (said at 1:08:25)

The statement accurately reflects standard audiological physiology and measurement methodology. Otoacoustic emissions (OAEs) are acoustic signals generated by outer hair cell motility within the cochlea and are routinely recorded non-invasively using a sensitive microphone probe inserted into the external ear canal.

1:08:45Jennifer Grohsupportedmoderate

The eardrum oscillates in precise time-locking with saccadic eye movements, with opposing displacement patterns in the two ears, carrying information about the horizontal and vertical metrics of the saccade.

"we were able to measure that the eardrum is—is basically moving in connection with—with every eye movement, every saccadic eye movement. ... The signal is very precisely time-locked to the onset of the eye movement and the effect, um, is different in the two ears, so that if your eyes are moving to the left, the eardrum on the right is going to kind of, uh, bulge inward, then outward, then inward. ... It turns out to carry information, uh, about how far the eyes are moving to the left or to the right, as well as a bit less, but some information about vertical movements as well" (said at 1:08:45)

The speaker accurately summarizes the discovery and characterization of eye movement-related eardrum oscillations (EMREOs) by her laboratory. Research in humans and non-human primates demonstrates that the tympanic membrane oscillates in precise temporal synchrony with saccadic eye movements (beginning around saccade onset). The oscillations exhibit opposite phase/displacement patterns depending on whether the eye movement is directed ipsilaterally or contralaterally (creating opposing patterns between the two ears), and their waveform parameters systematically encode both the horizontal and vertical metrics (displacement and direction) of the saccade.

1:14:15Jennifer Grohsupportedhigh

There are descending (centrifugal) neural projections from the brain to the retina in the visual system.

"There are descending connections from the brain to the retina itself that nobody understands." (said at 1:14:15)

Descending (centrifugal or retinopetal) projections extending from brain structures back to the retina are well-documented across vertebrates, including mammals and primates. Tracing studies have identified retinopetal neurons originating from hypothalamic, midbrain, and raphe nuclei. Furthermore, reviews confirm that while their anatomy and neurochemistry are established, the precise functional significance of these descending pathways remains incompletely understood and debated.

1:16:55Andrew Huberman (host)supportedhigh

The Grand Central whispering gallery allows a whisper to be clearly heard across diagonal corners approximately 25 feet away due to parabolic acoustic reflection along the domed ceiling.

"And there's also a hallway off to one side where you can go into a corner. ... And whoever you're with can go to the opposite diagonal corner. ... The ceiling is shaped like somewhat of a dome. ... but you are easily 25 ft away from this person that you're there with. ... And if you speak at a very, very low volume, they can hear you on the opposite side. ... And so obviously the sound waves are traveling along the ceiling on that parabola." (said at 1:16:55)

The host accurately describes the well-known acoustic phenomenon of the Whispering Gallery located outside the Grand Central Oyster Bar in Grand Central Terminal. The Guastavino-tiled vaulted ceiling functions as a whispering gallery: acoustic waves generated at one corner cling to and travel along the smooth, curved surface of the vault via successive grazing reflections (whispering gallery modes) directly to the opposite diagonal corner (~30 feet away), allowing low-volume whispers to be heard clearly across the space while remaining inaudible to people standing in the middle.

1:29:15Jennifer Grohsupportedmoderate

Humans have more distinct sensory cortical areas than monkeys and more distant mammalian relatives.

"we have many more sensory areas of the brain than monkeys do, than more distant mammalian relatives do, as if what might have happened to allow us to become so smart is to make extra copies of some of these sensory areas of the brain." (said at 1:29:15)

Comparative neuroanatomical studies and evolutionary reconstructions demonstrate that the number of distinct cortical areas—including sensory and sensory-association areas—increased markedly across mammalian evolution. Basal and early mammals possessed roughly 20 to 25 distinct cortical areas (consisting primarily of primary and secondary sensory fields), early primates and monkeys expanded these to around 50 or more distinct fields (especially within visual, somatosensory, and posterior parietal systems), and modern humans possess an estimated 150 to 200 distinct cortical areas per hemisphere.

  • supports: The evolution of the complex sensory and motor systems of the human brain. (Brain research bulletin 2008) · cited 174x in the literature
    "Evidence from comparative studies of cortical organization from small-brained mammals of the six major branches of mammalian evolution supports the conclusion that the small neocortex of early mammals was divided into roughly 20-25 cortical areas, including primary and secondary sensory fields. In early primates, vision was the dominant sense, and cortical areas associated with vision in temporal and occipital cortex underwent a significant expansion. Comparative studies indicate that early primates had 10 or more visual areas, and somatosensory areas with expanded representations of the forepaw. ... As larger brains evolved in early apes and in our hominin ancestors, the number of cortical areas increased to reach an estimated 200 or so in present day humans" (abstract, passage verified)
    pubmedfull study (doi)
  • supports: The evolution of brains from early mammals to humans. (Wiley interdisciplinary reviews. Cognitive science 2013) · cited 271x in the literature
    "This small cap of neocortex was divided into 20-25 cortical areas, including primary and some of the secondary sensory areas that characterize neocortex in nearly all mammals today. ... Early primates evolved from small-brained, nocturnal, insect-eating mammals with an expanded region of temporal visual cortex. ... Neocortex was greatly expanded and included an array of cortical areas that characterize neocortex of all living primates. Specializations of the visual system included new visual areas that contributed to a dorsal stream of visuomotor processing" (abstract)
    pubmedfull study (doi)
  • supports: The origin and evolution of neocortex: From early mammals to modern humans. (Progress in brain research 2019) · cited 48x in the literature
    "Human neocortex evolved in a series of ancestors with less neocortex and fewer cortical areas. Thus, early mammals had little neocortex and roughly 20 cortical areas, while early primates had much more cortex and around 50 cortical areas. Humans have the largest of primate brains that is 80% neocortex with about 200 areas." (abstract, passage verified)
    pubmedfull study (doi)
1:13:00Andrew Huberman (host)supportedvery low

The genetic programs expressed in motor neurons controlling trunk musculature are homologous to those in undulating fish, representing conserved ancestral motor circuits upon which limb- and digit-controlling motor neurons evolved.

"the evolutionary history of the genes that—that are expressed in like the motor neurons that move the trunk are the same ones that undulating, uh, fish use. And actually, this will get us back to sound, I promise. And then there's the—these additional layers of motor neurons that have been added through evolution: the ones that flap the fins, and then the final addition are the motor neurons that control fine movement of the fingers." (said at 1:13:00)

Comparative developmental neurobiology demonstrates that the core genetic transcriptional programs defining medial motor neurons (which innervate axial/trunk musculature) are ancient and conserved across early aquatic vertebrates, including jawless fish (lampreys) and cartilaginous fish. As paired fins and tetrapod limbs/digits evolved, evolutionary diversification involved novel transcriptional enhancers (such as E2 for lateral motor column neurons) and conserved Hox regulatory programs that were layered onto these ancestral axial motor circuits.

  • supports: Functional Diversification of Motor Neuron-specific Isl1 Enhancers during Evolution. (PLoS genetics 2015) · cited 25x in the literature
    "Functional diversification of motor neurons has occurred in order to selectively control the movements of different body parts including head, trunk and limbs... Interestingly, the core region of E1 has been conserved in evolution, even in the lamprey, a jawless vertebrate with primitive motor neurons. All E1 sequences from lamprey to mouse responded equally well to Phox2a and the Isl1-Lhx3 complex. Conversely, E2, the enhancer for limb-innervating motor neurons, was only found in tetrapod animals." (abstract)
    pubmedfull study (doi)
  • supports: The Ancient Origins of Neural Substrates for Land Walking. (Cell 2018) · cited 102x in the literature
    "This network encodes peripheral connectivity modules that are distinct from those used in axial muscle-based swimming and has apparently been diminished in most modern fish. These findings indicate that the circuits that are essential for walking evolved through adaptation of a genetic regulatory network shared by all vertebrates with paired appendages." (abstract, passage verified)
    pubmedfull study (doi)
1:19:50Jennifer Grohsupportedmoderate

Humans do not have superior visual or auditory sensory acuity compared to monkeys.

"We don't really see or hear any better than monkeys do. So what's this extra tissue doing for us? Possibility is that we're using it to generate these simulations and that running these simulations is kind of what thought is." (said at 1:19:50)

Comparative psychophysical and sensory physiology studies show that basic visual acuity and auditory processing in humans are very similar to those of Old World monkeys (such as macaques). Extrapolated visual acuity does not differ significantly between humans and macaques (~27.3 vs. 26.1 cycles per degree, p = 0.763), though humans demonstrate higher peak contrast sensitivity. Similarly, auditory modulation transfer functions and spectral-temporal sound processing show analogous thresholds and perceptual strategies across both species (with macaques having higher upper-frequency limits and similar mid-frequency sensitivity).

1:32:27Jennifer Grohsupportedmoderate

A typical vocabulary size for a young adult/college student is approximately 30,000 words.

"And you know, these are kids that probably have a 30,000-word vocabulary, right? That's a typical vocabulary. Young brains." (said at 1:32:27)

Large-scale lexical studies in linguistics and psycholinguistics support the estimate that young adults/college-age native English speakers possess a vocabulary in the range of ~30,000 to 42,000 words (lemmas/word types). For example, Brysbaert et al. (2016) analyzed literature estimates and a large crowdsourcing dataset, determining that an average 20-year-old native speaker of American English knows approximately 42,000 lemmas (ranging from 27,000 in the lowest 5% to 52,000 in the highest 5%), or about 11,100 word families, placing a ~30,000-word estimate well within typical empirical ranges depending on the exact linguistic definition of 'word'.

1:39:10Andrew Huberman (host)supportedmoderate

Augmenting acetylcholine improves attention, and basal forebrain structures like the nucleus basalis that release acetylcholine are necessary to establish an attentional spotlight.

"if you can augment acetylcholine, you can improve attention. It's just so clear that these forebrain structures like nucleus basalis that are releasing acetylcholine, they're necessary but not sufficient to establish an attentional spotlight." (said at 1:39:10)

Extensive neurobiological and pharmacological evidence supports the claim. Cholinergic projections from the basal forebrain (including the nucleus basalis of Meynert) to sensory and frontoparietal cortices are well established as critical modulators of attentional processing and signal detection. Cortical cholinergic modulation alters population neural activity (mimicking directed attention and sharpening cortical representation), and augmenting acetylcholine transmission (via acetylcholinesterase inhibitors or receptor agonists) reliably enhances performance on attentional tasks across animal models and human trials.

1:40:21Andrew Huberman (host)supportedhigh

The cortex is rich with nerve endings of acetylcholine-releasing neurons, and the colliculus receives acetylcholine input.

"the cortex is you know rich with the the nerve endings of these acetylcholine releasing neurons. The colliculus has acetylcholine input" (said at 1:40:21)

Extensive neuroanatomical and neurochemical evidence confirms that the cerebral cortex receives dense cholinergic innervation (primarily originating from the basal forebrain) and that the colliculus (both superior and inferior colliculi) receives robust cholinergic afferent input (from brainstem nuclei such as the pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus, and parabigeminal nucleus).

1:40:44Andrew Huberman (host)supportedhigh

Norepinephrine's general function in the brain and body is to raise overall alertness.

"You have norepinephrine to raise overall alertness in the brain and body. That seems to be its general function." (said at 1:40:44)

The speaker's statement accurately reflects established neurobiology and physiology. Central norepinephrine release (primarily from the locus coeruleus) and peripheral sympathetic noradrenergic signaling function fundamentally to promote arousal, wakefulness, vigilance, and systemic alertness across the brain and body.

1:44:40Andrew Huberman (host)supportedmoderate

Even a slight degree of dehydration can diminish cognitive and physical performance.

"Even a slight degree of dehydration can diminish your cognitive and physical performance." (said at 1:44:40)

Multiple systematic reviews and meta-analyses demonstrate that mild to moderate hypohydration/dehydration (1% to >2% body mass loss) impairs both cognitive functions (particularly attention, executive function, and motor coordination) and physical performance (including aerobic performance, muscular endurance, and strength).

1:39:09Andrew Huberman (host)supportedhigh

Working memory is primarily modulated by dopamine signaling.

"There's some very interesting data coming out of Mark D'Esposito's lab. We've had him on the podcast before about dementia and ways to improve working memory, which seems to be more of a dopamine thing." (said at 1:39:09)

Extensive cognitive neuroscience research—prominently including work from Mark D'Esposito's laboratory—demonstrates that working memory functions in the prefrontal cortex and striatal circuits are heavily modulated by dopamine signaling. Human pharmacological fMRI studies and reviews establish that dopamine neuromodulation regulates working memory maintenance, cognitive stability, and resistance to distraction, typically operating via an inverted-U-shaped dose-response relationship.

1:59:00Andrew Huberman (host)supportedmoderate

Ground-feeding birds perform inward vergence eye movements to accurately target small seeds or insects as their heads descend.

"Turns out that any birds that eat off the ground have a very complex like sensorimotor challenge that my colleague the late he died of old age. Harvey Karten told me about which is, you know, they got this tiny beak and the seed is small and they, you know, you and I could pick up things off a table and and pretty quickly, but they're doing this with this tiny beak, but their eyes are on the side of their head. So, in order to do that, as their head descends really fast, in order to not smash their beak into the surface and make an accurate pickup of the seed or whatever it is, they or bug, their eyes undergo a vergence eye movement." (said at 1:59:00)

Experimental research on avian vision demonstrates that lateral-eyed, ground-feeding birds such as pigeons undergo coordinated binocular vergence eye movements when focusing on objects in their frontal binocular field during feeding/pecking tasks. Studies show pigeons utilize distinct oculomotor modes, including coordinated frontal vergence movements to accurately fixate and peck at targets in the near binocular field.

1:51:22Andrew Huberman (host)supportedhigh

Adrenaline and arousal influence cognitive focus according to an inverted U-shaped curve, where focus is impaired at both very low and very high levels.

"Because adrenaline was what, this like inverted U-shaped thing. Like at very low levels, we can't focus. At higher levels we can focus and it gets too high we're discombobulated." (said at 1:51:22)

Extensive neurobiological and psychological research supports the inverted U-shaped relationship between catecholaminergic arousal (norepinephrine/noradrenaline and dopamine) and cognitive functions governed by the prefrontal cortex, including attention and working memory. Low levels of catecholamines (such as during fatigue or drowsiness) and excessively high levels (such as during acute stress) impair prefrontal cortical network firing and cognitive focus, whereas moderate/optimal levels enhance signal-to-noise processing and focus.

2:08:58Andrew Huberman (host)supportedhigh

Viewing morning sunlight sets the human circadian rhythm.

"GUEST1: I know I should go outside and touch grass and get some sunlight. I know. I know. HOST: Set that circadian rhythm." (said at 2:08:58)

Light is established in chronobiology as the primary zeitgeber (synchronizing cue) for entraining the human circadian system to the 24-hour solar day. Controlled human experimental trials demonstrate that morning light exposure falls on the phase-advance portion of the human circadian phase response curve, shifting the timing of central circadian markers (such as the dim-light melatonin onset and core body temperature minimum earlier) and stabilizing circadian phase.

Unverified means no publication matching the claim was located; it does not prove the claim false. Spotted an error? See the corrections policy - disputes from the people quoted are prioritized.