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Why do we need sleep

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It is not because the body is tired

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It is because you are too expensive

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Have you ever considered something strange

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Every night you die for about eight hours

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Your consciousness disappears

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You do not know who you are

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You do not know where you are

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You do not know time is passing

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Then the alarm rings in the morning

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And you come back to life

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All eight billion people in the world

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Go through this little death every day

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Do you not find that strange

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Even stranger

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If you do not die

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If you stay awake for days

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You really can die

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In 1989

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At the University of Chicago

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Allan Rechtschaffen

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Conducted a disturbing experiment

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He forced rats to stay awake with a device

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And prevented them from sleeping

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The result was

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Every sleep deprived rat

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Within eleven to thirty two days

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Died or was near death

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No single organ failure killed them

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Their entire system collapsed

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Their weight plummeted

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Temperature control failed

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Skin ulcers appeared

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Their immune systems collapsed

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As if the body forgot how to be a body

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So sleep is not optional

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It is a matter of life and death

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But why

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During those eight hours without awareness

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What essential work is the body doing

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And

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The deeper question is whether consciousness really switches off

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Or perhaps

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Consciousness is not what switches off

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But something else

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Hello

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Everyone

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I am Leo Wang

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This question

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Has only recently gained a fairly complete scientific answer

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And a fierce debate erupted in 2024

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Overturning what seemed settled

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Let me show you the latest full picture

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The first answer

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Is physical cleaning of the brain

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In 2012

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At the University of Rochester

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The team of Maiken Nedergaard

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Discovered a system that stunned neuroscience

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The glymphatic system

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They found

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When mice enter deep sleep

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Glial cells in the brain shrink

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The space between cells expands by about sixty percent

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Cerebrospinal fluid rushes in

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Washing away metabolic waste like a street sweeper

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Most importantly beta amyloid

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This is the hallmark pathological protein

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Of Alzheimer disease

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In January 2025

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The Nedergaard team

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In the journal Cell

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Published a major paper

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Revealing the precise cleaning mechanism

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During deep sleep

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The brainstem releases norepinephrine waves about every fifty seconds

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These tiny chemical pulses

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Make cerebral blood vessels

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Rhythmically contract and relax

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Like a slow pump

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With every contraction

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Cerebrospinal fluid enters spaces around the vessels

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Carrying waste away

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This rhythmic brain washing process

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Is a core physical function of deep sleep

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But in 2024

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At Imperial College London

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The team of Nicholas Franks

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In Nature Neuroscience

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Published a paper

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That directly challenged this view

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They tracked molecules in brain tissue with fluorescent markers

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And reached a conclusion that rocked the field

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Brain clearance did not increase during sleep and anesthesia

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It decreased

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Franks argued

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Molecules move through brain tissue mainly by passive diffusion

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Not active fluid flushing

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The Nedergaard team immediately responded

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Criticizing the method used by Franks

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Injecting fluorescent dye

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Directly into brain tissue

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May have disrupted

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Natural fluid dynamics

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The debate remains unresolved

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But in 2026

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A study in Nature Communications

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Using human participants

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Provided important evidence

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After normal sleep

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Morning plasma levels

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Of beta amyloid and tau proteins

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Were significantly higher

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Than after sleep deprivation

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This suggests sleep truly promotes

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Waste transfer from the brain to the blood

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That is how science works

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It does not fear debate

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Debate is part of its calibration process

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Even while details of the cleaning mechanism remain disputed

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One thing is certain

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Chronic sleep loss is strongly linked to Alzheimer risk

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The brain needs offline maintenance to process waste

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No one disputes that broad conclusion

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The second answer

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Is synaptic pruning and recalibration

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At the University of Wisconsin

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Giulio Tononi

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And Chiara Cirelli

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Proposed the synaptic homeostasis hypothesis

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The central idea is intuitive

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Every new thing you learn during the day

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Every experience you have

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Every decision you make

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Strengthens synaptic connections a little

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By the end of the day

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Synaptic strength across the brain

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Has risen too high

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Like a computer

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Running too many programs

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With memory almost full

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The role of sleep

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Is synaptic downscaling

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Weakening unimportant connections

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And restoring a healthy signal to noise ratio

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Meanwhile

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Truly important memories

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Move from the hippocampus to the cortex

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For long term storage

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That is why sleeping after learning

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Makes memory stronger not because sleep strengthens it

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But because sleep clears the noise

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So the real signal stands out

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All right

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The first two answers

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Are washing and pruning

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Clearing waste and pruning synapses

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These are important

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But they do not answer a deeper question

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Why must this work happen while your awareness disappears

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Could you not simply lie still with your eyes closed

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Without moving

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And still clean and prune

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Why must the brain switch you off first

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This brings us to the third answer

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And the deepest point

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Of this video

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Your brain needs

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To temporarily shut down the machinery of self

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We need predictive coding to understand this

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As we discussed in the episode

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Your self is a hallucination made by the brain

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That we covered before

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Your brain is not a passive receiver

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It is an active prediction generator

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Constantly creating a controlled hallucination of the world

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Then calibrating it with sensory data

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This process itself consumes enormous energy

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The brain is only two percent of body weight

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Yet uses twenty percent of all bodily energy

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Within this prediction system

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What consumes the most energy

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The default mode network or DMN

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The core network sustaining your narrative self

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Who I am

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What I have done

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What I will do

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What others think of me

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That endless inner monologue

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Is driven by this network

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You think your brain rests while you daydream

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Quite the opposite

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The default mode network is most active then

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It keeps weaving stories about you

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This leads to a profound conclusion

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The costliest part of waking life is not sensing the world

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But maintaining the virtual character called self

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Your brain spends vast energy every day

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Maintaining the narrative structure called me

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My memories

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My identity

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My plans

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My anxiety

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My expectations

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These heavily weighted prior beliefs keep running

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Keep consuming synaptic resources

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And keep generating prediction errors

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During deep sleep

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Research has found

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Functional connections within the default mode network

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Change significantly

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Especially frontal involvement

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Which drops sharply

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The self narrative engine finally pauses

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The brain stops spending energy maintaining your character

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All those resources are released

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For cleaning pruning and memory consolidation

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Here is an analogy

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The waking you

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Is like a company open for business

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Every light is on

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The air conditioning runs at full power

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Every employee is at work

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Customers stream in and out

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Of course you cannot

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In that state

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Thoroughly clean and maintain the building

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Or service its equipment

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You must close lock the doors and send everyone home

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Before the cleaners can work

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Sleep

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Is closing time

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And the one who must leave

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The manager using the most resources

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Is you the self narrative system

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Now we reach the most interesting question

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During this shutdown

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Does consciousness completely disappear

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The answer is

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No

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First

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During REM sleep you dream

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Brain activity approaches the waking state

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You have vivid visual emotional and narrative experience

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In dreams you run fear love and fly

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Some form of consciousness is clearly active

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More surprising is non REM sleep

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Recent EEG research has found

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Even in the deepest slow wave sleep

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People have windows of conscious experience

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In 2025

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Published in Nature Communications

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The DREAM database project

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Analyzed more than twenty six hundred sleep awakenings

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And found

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People awakened from non REM sleep

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Also often reported

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Vague conscious experiences

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Not complete dreams

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But some sense of presence

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Researchers even found

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That EEG signals

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Could predict whether someone

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Upon awakening

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Would report conscious experience

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More extreme evidence comes from yogic traditions

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Practitioners of Indian yoga nidra

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While showing the EEG state of deep sleep

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Maintain waking awareness

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In 1971

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The renowned Swami Rama

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At the Menninger Foundation laboratory in America

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Demonstrated this ability

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Connected to an EEG machine

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He deliberately entered

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A brain state dominated almost entirely by delta waves

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The hallmark of deep sleep

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Yet after returning to normal waking awareness

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He could repeat word for word

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A conversation during the experiment

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In the next room

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Between two technicians

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His body was deeply asleep

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His brain was doing deep sleep maintenance

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Yet some form of awareness remained

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I must clarify

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Although this experiment was widely documented

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It was not published in a peer reviewed journal

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It is a compelling case report

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Not rigorous scientific evidence

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But the direction it points toward

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Matches the windows of consciousness in non REM sleep

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Found by modern EEG research

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Indian philosophy

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Calls this state Turiya

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The fourth state of consciousness

297
00:10:28,964 --> 00:10:31,703
Beyond waking dreaming and deep sleep

298
00:10:31,885 --> 00:10:32,764
It is not waking

299
00:10:32,964 --> 00:10:33,943
Not dreaming

300
00:10:34,005 --> 00:10:35,624
Not unconscious deep sleep

301
00:10:35,765 --> 00:10:40,152
It is pure being with awareness but no content

302
00:10:40,414 --> 00:10:44,713
This fits perfectly with the predictive coding framework

303
00:10:45,213 --> 00:10:47,012
Recall the three nature model

304
00:10:47,613 --> 00:10:50,673
Other dependent nature is the raw flow of sensory data

305
00:10:50,853 --> 00:10:54,752
Imagined nature is the narratives and labels added by the brain

306
00:10:54,973 --> 00:10:58,593
Perfected nature is knowing this whole process as it is

307
00:10:58,934 --> 00:11:00,953
What happens during deep sleep

308
00:11:00,973 --> 00:11:02,872
In the language of predictive coding

309
00:11:02,894 --> 00:11:04,853
Is that the weight of imagined nature

310
00:11:04,853 --> 00:11:06,012
Is turned far down

311
00:11:06,454 --> 00:11:08,673
Those prior beliefs about me

312
00:11:08,694 --> 00:11:09,992
Temporarily go offline

313
00:11:10,213 --> 00:11:14,392
But the underlying dependent flow continues as your heart beats

314
00:11:14,414 --> 00:11:15,912
Your breathing continues

315
00:11:15,973 --> 00:11:18,073
Your temperature regulation keeps working

316
00:11:18,694 --> 00:11:22,053
And at the deepest level of awareness in Buddhist terms

317
00:11:22,054 --> 00:11:27,185
That unborn undying luminosity may never go out

318
00:11:27,486 --> 00:11:30,324
What yogis achieve through long training

319
00:11:30,325 --> 00:11:31,224
In essence

320
00:11:31,246 --> 00:11:32,444
Is taking Turiya

321
00:11:32,725 --> 00:11:34,685
From a state that only appears

322
00:11:34,685 --> 00:11:36,165
Occasionally in deep sleep

323
00:11:36,166 --> 00:11:38,545
Into a stable abiding state

324
00:11:38,886 --> 00:11:42,265
They learn to keep cleaning and maintenance running

325
00:11:42,286 --> 00:11:44,826
While preserving the deepest light of awareness

326
00:11:45,167 --> 00:11:47,367
This gives us a profound insight

327
00:11:47,767 --> 00:11:50,507
You do not sleep because consciousness needs rest

328
00:11:50,687 --> 00:11:53,107
Consciousness may not need rest at all

329
00:11:53,328 --> 00:11:54,926
What truly needs rest

330
00:11:54,927 --> 00:11:58,027
Is the advanced application called self

331
00:11:58,488 --> 00:11:59,086
Here is an analogy

332
00:11:59,448 --> 00:12:03,347
Your phone operating system can run forever without shutting down

333
00:12:03,488 --> 00:12:05,987
But if fifty applications run at once

334
00:12:06,047 --> 00:12:09,906
Each refreshing sending alerts and using memory

335
00:12:10,007 --> 00:12:13,267
The phone heats up slows down and loses power

336
00:12:13,448 --> 00:12:15,406
You do not need to stop the operating system

337
00:12:15,407 --> 00:12:17,227
You need to close those applications

338
00:12:17,927 --> 00:12:18,367
The self

339
00:12:18,568 --> 00:12:19,607
Your story of who I am

340
00:12:19,887 --> 00:12:20,647
What I want

341
00:12:20,848 --> 00:12:22,086
What others think of me

342
00:12:22,088 --> 00:12:23,967
That endless narrative loop

343
00:12:24,328 --> 00:12:25,446
Is the largest application

344
00:12:25,448 --> 00:12:26,086
And the most

345
00:12:26,248 --> 00:12:27,946
Resource intensive application in your brain

346
00:12:28,047 --> 00:12:28,446
Sleep

347
00:12:28,687 --> 00:12:30,853
Force closes this application

348
00:12:31,194 --> 00:12:32,214
While meditation

349
00:12:32,315 --> 00:12:36,893
Teaches you to close it voluntarily while awake

350
00:12:37,194 --> 00:12:38,393
That is why

351
00:12:38,395 --> 00:12:42,074
Long term meditators often need less sleep

352
00:12:42,074 --> 00:12:43,714
Yet have more energy

353
00:12:44,114 --> 00:12:45,654
Because during the day

354
00:12:45,675 --> 00:12:47,834
They are already doing the core work

355
00:12:47,834 --> 00:12:49,473
Normally reserved for deep sleep

356
00:12:49,994 --> 00:12:52,814
Turning down the prior weight of self

357
00:12:52,874 --> 00:12:54,909
And giving the system room to breathe

358
00:12:55,371 --> 00:12:55,850
Think about it

359
00:12:56,130 --> 00:12:58,189
It is a beautiful symmetry

360
00:12:58,410 --> 00:13:00,209
Nature gave every living creature

361
00:13:00,211 --> 00:13:01,610
A compulsory mechanism

362
00:13:02,010 --> 00:13:02,409
Sleep

363
00:13:02,770 --> 00:13:05,169
To unload the self program regularly

364
00:13:05,530 --> 00:13:06,289
Free resources

365
00:13:06,691 --> 00:13:07,650
Clear waste

366
00:13:07,650 --> 00:13:10,949
While practitioners through millennia of introspection

367
00:13:11,010 --> 00:13:11,730
Discovered a path

368
00:13:12,010 --> 00:13:13,490
That requires no forced shutdown

369
00:13:13,810 --> 00:13:15,730
Yet achieves the same effect

370
00:13:16,130 --> 00:13:16,909
Stillness and insight meditation

371
00:13:17,211 --> 00:13:18,370
One path is passive

372
00:13:18,530 --> 00:13:19,929
The other is active

373
00:13:19,930 --> 00:13:22,870
One closes the business for eight hours each day

374
00:13:23,050 --> 00:13:27,409
The other learns maintenance during business hours

375
00:13:27,669 --> 00:13:28,749
And have you noticed

376
00:13:29,309 --> 00:13:31,629
This matches what we discussed in the episode

377
00:13:32,150 --> 00:13:34,188
What meditation does according to neuroscience

378
00:13:34,669 --> 00:13:35,789
The episode about

379
00:13:35,789 --> 00:13:36,708
The REBUS model

380
00:13:37,069 --> 00:13:38,208
It echoes it perfectly

381
00:13:38,669 --> 00:13:40,068
Robin Carhart Harris

382
00:13:40,069 --> 00:13:41,488
And Friston found

383
00:13:41,669 --> 00:13:44,068
That deep meditation changes the brain

384
00:13:44,589 --> 00:13:48,169
By lowering the precision weight of high level priors

385
00:13:48,549 --> 00:13:51,369
Activity in the default mode network drops sharply

386
00:13:51,789 --> 00:13:53,369
The sense of self dissolves

387
00:13:53,630 --> 00:13:56,228
This mirrors what happens during deep sleep

388
00:13:56,230 --> 00:13:57,649
At the neural level

389
00:13:57,669 --> 00:13:58,988
It is almost the same process

390
00:13:59,429 --> 00:14:00,549
Except meditation

391
00:14:00,549 --> 00:14:03,289
Does it voluntarily while awake

392
00:14:03,990 --> 00:14:04,308
So

393
00:14:04,630 --> 00:14:05,649
When you meditate

394
00:14:05,669 --> 00:14:07,308
Your brain is catching up on sleep during the day

395
00:14:07,709 --> 00:14:09,129
Not physical sleep

396
00:14:09,150 --> 00:14:11,925
But the sleep of unloading the self

397
00:14:12,396 --> 00:14:13,195
Finally

398
00:14:13,227 --> 00:14:16,366
I want to share something that moves me deeply

399
00:14:16,867 --> 00:14:20,845
We live in a culture that equates wakefulness with productivity

400
00:14:21,146 --> 00:14:24,465
Many see sleep as wasted time so get up and compete

401
00:14:24,465 --> 00:14:24,945
Get up and hustle

402
00:14:25,546 --> 00:14:28,166
But once you understand the true nature of sleep

403
00:14:28,227 --> 00:14:30,825
You see that this attitude is not only wrong

404
00:14:30,826 --> 00:14:31,845
But dangerous

405
00:14:32,186 --> 00:14:34,126
You are not wasting eight hours

406
00:14:34,146 --> 00:14:37,325
You are performing the most important system maintenance

407
00:14:38,186 --> 00:14:39,345
Every period of deep sleep

408
00:14:39,587 --> 00:14:40,705
Is your brain

409
00:14:40,707 --> 00:14:43,065
Practicing a small form of no self

410
00:14:43,507 --> 00:14:45,425
Recalibrating inflated prior weights

411
00:14:45,426 --> 00:14:46,565
Back to balance

412
00:14:46,587 --> 00:14:49,386
Returning excessive synaptic strength to baseline

413
00:14:49,387 --> 00:14:53,008
Washing away the neurotoxins created during the day

414
00:14:53,109 --> 00:14:55,268
Every night you practice letting go

415
00:14:55,828 --> 00:14:57,768
You simply do not know it

416
00:14:58,029 --> 00:15:00,567
And if while awake during the day

417
00:15:00,648 --> 00:15:01,428
You can also learn

418
00:15:01,428 --> 00:15:03,628
To occasionally pause the program called me

419
00:15:03,629 --> 00:15:04,508
For a few minutes

420
00:15:04,948 --> 00:15:06,548
Even just sitting quietly

421
00:15:06,548 --> 00:15:07,308
Without checking your phone

422
00:15:07,548 --> 00:15:08,268
Without dwelling on the past

423
00:15:08,509 --> 00:15:09,567
Without worrying about the future

424
00:15:09,629 --> 00:15:10,928
Simply watching thoughts

425
00:15:10,948 --> 00:15:12,107
Arise and dissolve

426
00:15:12,548 --> 00:15:13,788
Then during the day

427
00:15:13,789 --> 00:15:16,367
You give your brain a miniature deep sleep

428
00:15:16,548 --> 00:15:18,428
It cannot replace real sleep

429
00:15:18,428 --> 00:15:21,648
But before nightly maintenance arrives

430
00:15:21,668 --> 00:15:24,583
It keeps your system from reaching the edge of collapse

431
00:15:25,360 --> 00:15:26,896
This is probably why

432
00:15:26,956 --> 00:15:27,992
Every wisdom tradition

433
00:15:28,352 --> 00:15:30,345
Buddhism Daoism and Stoicism

434
00:15:30,585 --> 00:15:31,581
And Christian contemplation

435
00:15:31,941 --> 00:15:33,298
Teach the same thing

436
00:15:33,737 --> 00:15:34,793
Become still

437
00:15:35,053 --> 00:15:37,266
Not because stillness has mystical power

438
00:15:37,406 --> 00:15:41,314
But because stillness is your brain asking for room to breathe

439
00:15:41,913 --> 00:15:44,406
Your consciousness never shut down

440
00:15:44,625 --> 00:15:45,422
What shut down

441
00:15:45,423 --> 00:15:47,218
Was always that self important me

442
00:15:47,737 --> 00:15:48,453
I am Leo Wang

443
00:15:48,654 --> 00:15:49,372
See you next time