Dr. David Eagleman on Neuroplasticity, Time Perception, Memory and Why We Dream

High-Level Overview

Andrew Huberman sits down with neuroscientist and author Dr. David Eagleman for a wide-ranging tour of how the brain rewires itself and what that means for ordinary life. The conversation starts with neuroplasticity: why humans arrive in the world with what Eagleman calls a half-baked brain, why the cortex can be repurposed, and what adults can do to keep changing. From there it moves to the tug of war between our present and future selves and Eagleman's idea of the Ulysses contract, then to time perception, including his well-known experiment of dropping volunteers from a 150-foot tower to find out whether time really slows down when we fear for our lives.

The second half covers sensory substitution (hearing through the skin, seeing through the tongue), a new theory of why we dream, how unreliable memory is and what that means for courtrooms, and finally the neuroscience of in-groups, out-groups and polarization. The tone is curious, upbeat and story-driven; Eagleman explains nearly everything through an experiment or an anecdote, and he is noticeably optimistic about the internet and AI as learning tools. The conversation flows from laboratory findings to personal habits to big social questions, with Huberman adding his own practices and speculative questions along the way.

The Discussion Explores:

• Why the human cortex is flexible "real estate" that gets defined by whatever is plugged into it
• Early specialization versus broad experience, and why critical thinking and creativity are the skills Eagleman would teach every child
• How adults keep plasticity alive: novelty, challenge, and stopping an activity once you are good at it
• The Ulysses contract: binding your future self so it cannot behave badly
• Why time seems to run in slow motion during a scare, and why summers shrink as we age
• Sensory substitution and addition, from a vibrating wristband for deaf people to a compass belt
• Eagleman's hypothesis that dreams defend the visual cortex from being taken over at night
• Memory drift, eyewitness testimony, and the brain's weaker empathy for out-groups

Deep Dive into Main Ideas

A half-baked brain and a one-trick cortex

Eagleman describes neuroplasticity as nature's big trick with humans: drop a creature into the world with an unfinished brain and let the world wire up the rest. He says the brain has 86 billion neurons, each contacting on average 10,000 neighbors, and that those connections are constantly plugging, unplugging and changing strength. An alligator born 30,000 years ago would be the same alligator, he says, while a human with identical DNA born then would be a very different person, because culture, language and experience are absorbed into the circuitry. Each generation absorbs what earlier ones discovered and springboards from there.

He corrects the common picture that humans are special mainly because of the prefrontal cortex. In his telling it is cortex in general: humans have four times as much as our nearest animal relatives, and it is the same six-layered circuitry everywhere. In his words, "cortex is a one-trick pony" that becomes visual or auditory depending on which cable is plugged in. He cites a 2000 study by Mriganka Sur at MIT in which a ferret's visual input was rerouted into what would have been auditory cortex, and that tissue became visually responsive. More cortex puts more room between input and output, which lets us hold back from the food in front of us, and the prefrontal part lets us simulate possible futures without risking our lives.

Both men agree that no cortical real estate lies fallow. In people born blind, the visual cortex is taken over by hearing, touch and memory, and Eagleman says they can discriminate sounds and touch more finely; deaf people can become good enough at lip reading to tell where in the country a speaker is from. He mentions one hypothesis about savantism in autism along the same lines: a great deal of territory devoted to one thing, such as the piano or a Rubik's Cube, at a cost to other skills.

Specialists, generalists and what to teach children

Huberman brings up a recent study in Science suggesting that children who specialize very early in one sport or creative pursuit do not, on average, reach as high a peak later as those who did several things. Eagleman's response is mixed. He points to the Williams sisters and the Polgar sisters in chess as people drilled from the start who became champions, and explains why repetition works: practice moves a skill from the brain's software into its hardware, making it fast and cheap. If he played tennis against Serena Williams, he says, his brain would be the one burning the energy. He also notes a cost of spreading out: he says children raised with two or three languages end up with a smaller vocabulary in each than children raised with one, simply from less practice in each. Huberman still argues for learning a second language and an instrument, saying "Google Translate is not Google Relate".

Eagleman is enthusiastic about the internet for learning. His reasoning is that plasticity needs the right mix of neurotransmitters, and that mix lines up with curiosity and engagement. A child who gets an answer at the moment of curiosity retains it, unlike facts delivered on the teacher's schedule. He adds that phones at the dinner table let an argument continue past the point where nobody knows the answer.

Asked what builds a well-rounded brain, he offers two things. First, try to do well along every axis: athletic, scholarly and social, rather than, as he sees on airplanes, playing a phone game for the whole flight. Second, since nobody knows which careers will exist in 20 or 30 years, schools should concentrate on critical thinking and creativity. For critical thinking he proposes AI debate: a student argues a hot-button issue against an AI, is graded on the quality of the arguments, then switches sides. For creativity he suggests compressing the foundational material so the last week of each semester is spent remixing what was learned: bending, breaking and blending it into something new. He ties both to a saying he attributes to Goethe, that a parent can give a child roots and wings.

Keeping the adult brain plastic

Asked how to widen the capacity for plasticity, Eagleman answers in two words: "Seek novelty". The aim is to stay between "frustrating but achievable". He describes the Religious Orders Study in the Chicago area, in which nuns and priests agreed to donate their brains. Some nuns turned out to have Alzheimer's disease that nobody had noticed while they were alive. His explanation is that they lived in convents into their 90s with chores, social responsibilities, games, singing and arguments, so that even as tissue degenerated their brains kept building new routes. He contrasts this with people who retire and sit in front of the television, and notes that other people are among the hardest things a brain deals with.

His advice to an older person who does crossword puzzles: "it's good until you get good at it", and then move to something you are bad at. The reason, he says, is that the brain sits in silence and darkness building a model of the world, and its goal is to stop changing once its predictions work. Huberman adds that the agitation and frustration of learning reflect the release of chemicals such as adrenaline and act as a signal that change is needed.

On the chemistry, Huberman asks why raising any of several neuromodulators seems to open a window of plasticity. Eagleman thinks science will eventually see them as combination locks rather than single agents, though acetylcholine looks to him like the main one: broadcast widely in a baby, dabbed locally in an adult, like a pointillist painter. He cautions that turning these dials has surprises, citing Parkinson's patients on dopamine-raising medication who became compulsive gamblers. He also says some regions lock down early (the primary visual cortex) while downstream areas, such as those recognizing faces, stay plastic for life; he compares the primary areas to a software kernel no one touches. Huberman raises psychedelics, saying he sees therapeutic potential but knows of people changed for the worse after a few uses, and concludes "Directed plasticity is the goal". Eagleman agrees and adds that nobody would really want an infant's total plasticity, because we are the sum of our memories and skills.

The Ulysses contract and the future self

Eagleman calls the ability to think about our future selves the most special part of being human. He describes the brain as a set of rival voices: one part wants the cupcake, one wants to stay fit, one bargains. Because we learn that our future self will behave badly in certain situations, we can act now to tie its hands. He names this after Ulysses, who had his men lash him to the mast and plug their own ears so he could hear the sirens without wrecking the ship, and says it is the subject of his next book.

Huberman's own example is keeping social media on a separate old phone and locking it in a timed box for hours, something he says has raised his productivity, attention and happiness. Eagleman's examples include a woman who froze her cash in a block of ice, arranging to meet a friend at the gym so you have to show up, a boot camp whose members jog to your lawn and shout your name if you skip, and a smoker who gave a friend a $10,000 check to be donated to an organization she found abhorrent if she was caught smoking. He notes the advice given to people with alcohol or drug problems to clear the house of alcohol and carry little cash. His summary: "I don't think we can trust our future selves". He says the same tools apply to positive goals, since New Year's resolutions rarely last, and mentions sites where you stake money on a target and the friction-removing ideas of James Clear, such as leaving running shoes by the door. Asked why Huberman is always late, he prescribes a commitment to always be five minutes early.

Inner voices and aphantasia

The discussion of inner chatter leads to individual differences. Eagleman says nearly anything neuroscience measures falls on a spectrum. His wife hears a constant inner radio; he hears no inner voice. The same goes for mental imagery, from aphantasia (no picture at all) to hyperphantasia (seeing it like a movie), usually scored from one to five. Huberman places himself in the middle, seeing a pale silhouette.

Eagleman, who says he is aphantasic himself, tells a story about Ed Catmull, who started Pixar. Catmull discovered he was aphantasic, gave a questionnaire to people at Pixar, and found that most of his best directors and animators were too. Eagleman's hypothesis is that a child who cannot summon the image of a horse has to stare at the real thing and work out how it is built, and gets more practice at drawing as a result.

Huberman then asks whether society benefits from people being siloed into specialties. Eagleman answers with an ice cream cone image: genetics, childhood, culture and era set the limits of the cone, and within it we can take many trajectories. He recalls his father, a psychiatrist, saying a parent's job is to open doors, and quotes Kierkegaard: "every man starts as a thousand men and dies as one". Both connect that to the way the brain overconnects in the first two years and is then pruned by experience.

Why time slows down in a fall

Huberman describes a perceptual exercise of his own: shifting attention from the inside of the body to something at a distance to the planet as a whole, to practice moving between time scales. Eagleman likes it, says he knows of no data on it, and explains that the brain has no single clock; different mechanisms handle subseconds, seconds and long eras, and the feel for long spans is learned with age.

He says people are poor at judging time and that much of it is illusory. At eight he fell off a roof, and the fall seemed to take a very long time while he calmly thought about Alice falling down the rabbit hole. Later he tested this by dropping 23 volunteers backwards from a 150-foot tower into a net (after doing it three times himself), each wearing a wrist device flashing numbers just faster than can normally be read. People did not see any faster during the fall. Yet when they judged the duration afterwards, their own fall felt much longer than someone else's. His conclusion is that it is a trick of memory: in an emergency the amygdala lays down a second, denser memory track, and when the brain reads back so much detail it infers that more time passed.

He applies that to aging. A child's summer is full of firsts and leaves a lot of footage; an adult's is not. He rejects the proportion-of-life explanation, because one unusual weekend feels long too. That makes it partly controllable, and his own habits are brushing teeth with the other hand, driving a different route home, and rearranging the office or swapping paintings. Huberman suggests the Ulysses contract and being present might seem to conflict; Eagleman argues that contracts free you to be present because the future is already handled.

Addiction, heartbreak and screens

Huberman offers his working definition of addiction as a progressive narrowing of the things that bring pleasure. Eagleman, drawing on his book Livewired, frames addiction as plasticity: the brain upregulates receptors for a drug because it now expects the world to contain it, and withdrawal follows when it is gone. He compares this to heartbreak, the painful readjustment when a person the brain expected is no longer there.

On social media he is torn. People once said the same about television. Much online content is well made and matched to our interests, yet people rarely feel good after scrolling, which resembles going back for a high that no longer arrives. Both men praise YouTube and AI tools for learning; Eagleman says he learns every home repair there.

New senses, and why we dream

Eagleman describes the wristband he built at Neosensory, a company he says he sold six months earlier, which turns sound into patterns of vibration on the skin so deaf people can learn to hear through it. One user, after about six months, told him of a dog's bark, "No, no, I hear the dog bark out there". He traces the idea to the 1880s and to Paul Bach-y-Rita's 1969 Nature paper, in which blind people in a dental chair felt a camera's image poked into their backs, and to the BrainPort, which puts the image on the tongue. He adds a compass belt built by colleagues at Osnabruck that buzzes toward north, and his Potato Head theory that the brain will work out any peripheral device plugged into it. Huberman recommends Ed Yong's book An Immense World on animal senses, and they note that sighted people can learn to echolocate.

His dream theory builds on this. In a Harvard experiment, he says, blindfolded people showed activity in the visual cortex in response to touch and sound within 60 to 90 minutes, thanks to existing cross-wiring he calls "silent sentinels". Since the planet turns into darkness every night, vision alone is at risk, so he and his student hypothesize that "dreams are the brain's way of defending the visual cortex against takeover from the other senses", through bursts of activity roughly every 90 minutes. They compared 25 primate species and report that the more plastic the species, the more REM sleep it has; human infants spend half their sleep in REM. Blind people still dream, he says, but in touch and sound.

Memory, the law and polarization

On whether a stressed victim remembers better, Eagleman says victims often have weapon focus and cannot describe a face, and that even emotional memories drift. He cites Elizabeth Phelps's interviews after September 11, repeated over ten years, in which memories of that day drifted as much as memories of the day before. He describes how officers can inflate a witness's confidence, why witnesses are separated, and his annual classroom demonstration in which a hired actor interrupts and students later "remember" a mole he invented. Courts, he says, can only educate jurors, who are still swayed by a witness who says "I know what I saw". He adds that children are more open to memory manipulation and describes Elizabeth Loftus's lost-in-the-mall studies.

On polarization, Eagleman argues we are no more polarized than in the 20th century, only more aware of other views. In his lab's scans, watching a hand stabbed with a needle triggers an empathic response, larger for a hand labelled with one's in-group and smaller for out-groups, among atheists too, and even with arbitrary teams assigned by a coin toss. Huberman wonders whether reactions to an out-group's good fortune would be more telling; Eagleman says he knows of no such experiment. He mentions capuchin monkeys enraged by a neighbour's better reward, and stresses that propaganda everywhere works by describing a group as animals or vermin, which quiets the networks that care about people. He hopes the next generation will respond, "wait a minute, I've heard that trick before". His remedies: teach the limits of our own internal models (the theme of another planned book), blind our biases as orchestras do with auditions, and complexify relationships by building cross-cutting ties, as an Iroquois peacemaker did with clans. He has patented a social media algorithm that surfaces what people share first. When Huberman hopes intermarriage will dissolve divisions, Eagleman replies that history does not support it.

Conclusion

The thread running through this episode is that the brain is a model-builder that changes only when its predictions fail, and nearly every practical point follows from that. To keep learning, look for what is new and hard and move on once it becomes easy; to make life feel longer, lay down more memories by breaking routines; to become who you want to be, assume your future self will weaken and set up contracts now. Eagleman's research on time, senses, dreams and memory all point to how much of experience is constructed inside the skull, and his work on empathy shows how readily that construction sorts people into us and them. His answer is education: about the limits of memory, about the tricks of propaganda, and about how narrow each person's own slice of the world really is.

This is a summary of "Science & Tools of Learning & Memory | Dr. David Eagleman" from Huberman Lab, giving you the GIST so you can decide if you want the REST. Listen to the full episode.