What Happens When We Sleep?

Neuroscience of Sleep Studies – SBNeC · FALAN · LatBrain · SfN 2025 · Brain Bee

Human sleep unfolds in cycles alternating between non-REM (N1, N2, N3) and REM (tonic and phasic) stages, each with distinct physiological markers and subjective experiences. Neuroscience shows that body perception, feelings, and emotions vary according to the depth and type of sleep.

Non-REM Sleep: The Descent into Stillness

N1 – The Gateway Stage

• Body: Heavy, but prone to spasms (myoclonia). Often accompanied by a falling sensation.
  

• Feelings: Slight strangeness, as if “losing control” of the body.
  

• Emotions: Brief anxiety or surprise when jolted awake.
  

• Transitions: Entry = yawns, relaxation. Exit = wakes easily, recalls fleeting flashes.
  
  

N2 – The Threshold of Disconnection

• Body: Muscle tone reduced, sinking sensation in bed.
  

• Feelings: Quiet security, as though “vanishing from the environment.”
  

• Emotions: Neutral, restful calm. Diffuse mental images and sounds.
  

• Transitions: Entry = loss of time awareness. Exit = feels like a quick “shut-off.”
  
  

N3 – Deep Slow-Wave Sleep

• Body: Entirely heavy, difficult to move. Abrupt awakening causes confusion.
  

• Feelings: Absolute belonging to the body-territory, fused with bed/earth.
  

• Emotions: Nearly absent — a comforting emptiness.
  

• Transitions: Entry = sudden plunge into inner silence. Exit = groggy disorientation.
  
  

REM Sleep: The Theater of the Body and Emotions

Tonic REM – Silent Bodily Dramaturgy

• Body: Full atonia. Movement impossible, yet proprioception (APUS) reorganizes. Sensation of floating or immobility, sometimes cataleptic.
  

• Feelings: “I am body, but I cannot move” — an internal positional adjustment.
  

• Emotions: Serenity blended with strangeness; fear if awakened abruptly (sleep paralysis).
  

• Transitions: Entry = dissolution into a larger volume. Exit = sudden release or startle.
  
  

Phasic REM – The Theater of Feelings

• Body: Rapid eye movements, irregular breathing, micro-expressions.
  

• Feelings: Strong emotions (joy, anger, passion, fear) dramatized in vivid dreams.
  

• Emotions: Intensified affective immersion in narrative scenarios.
  

• Transitions: Entry = sudden emergence of vivid imagery. Exit = awakens with racing heart, rapid breathing, clear dream recall.
  
  

Practical Guide to Self-Perception in Sleep

• If the body jerks → N1
  

• If the body sinks and time vanishes → N2
  

• If waking is hard and confused → N3
  

• If paralyzed or floating silently → Tonic REM
  

• If living strong emotional stories → Phasic REM
  
  

Key Insight

Sleep is not mere rest but an active process of bodily, emotional, and cognitive reorganization. Interoception (feelings) and proprioception (body reference) are cyclically modulated, shaping both physiological restoration and the dramatic landscapes of dreams.

References (post-2020)

• Scarpelli, S., Alfonsi, V., Gorgoni, M., & De Gennaro, L. (2021). Insomnia and dreams: The role of sleep–wake continuum and emotional regulation. Nature and Science of Sleep, 13, 171–185.
  

• Lecci, S., Fernandez, L. M. J., & Lüthi, A. (2020). Cortical excitation and sleep–wake states: The dual role of slow oscillations. Trends in Neurosciences, 43(8), 526–536.
  

• Boyce, R., Williams, S., & Adamantidis, A. (2022). REM sleep and memory consolidation: A state-dependent process. Neuron, 110(1), 1–17.
  

• Bellesi, M., Bushey, D., & Tononi, G. (2021). Sleep and synaptic homeostasis: Structural evidence in the human brain. Nature Reviews Neuroscience, 22(6), 337–351.
  

• Wainstein, G., & Nir, Y. (2021). Sleep, dreams, and consciousness: An updated neuroscientific perspective. Current Opinion in Neurobiology, 67, 144–152.