How we sleep: Cells to circuits to physiology

Daniel J. Buysse, MD

UPMC Professor of Sleep Medicine

Professor of Psychiatry and Clinical and Translational Science

University of Pittsburgh School of Medicine

buyssedj@upmc.edu, www.sleep.pitt.edu

Summer SWIM

University of Pittsburgh

August 10-14, 2020

Conflict of Interest Disclosures

Type of Potential Conflict Details of Potential Conflict

Grant/Research Support None

Consultant Bayer, BeHealth Solutions, Cereve/Ebb Therapeutics, Emmi Solutions, Pear Therapeutics,

Weight Watchers International

Speakers’ Bureaus None

Financial support None

Licensing fees Pittsburgh Sleep Quality Index (PSQI), Daytime Insomnia Symptoms Scale (DISS),

Insomnia Symptoms Questionnaire (ISQ), Consensus Sleep Diary (CSD), SATED and

RU_SATED Scales

Educational products CME Institute, American Academy of Physician Assistants, Eisai

The presenter does not have any potential conflicts of interest to disclose

X The presenter wishes to disclose the following potential conflicts of interest:

X The material presented in this lecture has no relationship with any of these potential conflicts

This talk presents material that is related to one or more of these potential conflicts, and references are

provided throughout this lecture as support.

How we sleep: Cells to circuits to physiology

▪ What is sleep?

▪ How does the brain generate sleep?

▪ How is sleep regulated?

Essential Questions

Methods

What is sleep?

What is sleep?

What is the function of sleep?

To optimize adaptation and function at every level of biological organization:

▪ Molecular energy regulation▪ Cellular▪ Tissue, circuit▪ Organ, organ system▪ Systems physiology▪ Cognition, affect, learning▪ Behavior

What is sleep?

“A recurring, reversible neuro-behavioral state of relative perceptual disengagement from and unresponsiveness to the environment.”

3 behavioral characteristics: quiescence, reduced responsiveness, homeostatic regulation

Carskadon and Dement, Principles and Practice of Sleep Medicine, 2005

Sleep mechanisms and measurement: Levels of analysis

Level of analysis Examples Relevance

Genes GWAS; Candidate genes; Drosophila; Family, twin studies

Sleep characteristics and disorders; pathophysiology of disorders

Molecules Neurotransmitters; cytokines; proteins, cellular messengers

Sleep regulation; Pathophysiology, treatment mechanisms of disorders

Cells “Local sleep” in neurons and columns; sleep as an intrinsic process

Use-dependent increases in sleep intensity

Circuits and structures Arousal and sleep-promoting systems; cognition, emotion, attention networks

Sleep mechanisms; Pathophysiology, markers, treatment effects of disorders

Electrophysiology Homeostatic regulation; sleep continuity; Slow-Wave Sleep; REM sleep

“Objective” sleep characteristics ; disorder diagnosis, treatment response

Physiology Autonomic function; hormones; circadian regulation

“Objective” sleep characteristics ; disorder diagnosis, treatment response

Behavior and cognition Sleep behavior; beliefs and attitudes; attention-intention-effort

Psychological-behavioral models of sleep; effects of manipulations and disorders

Symptoms, self-report Sleep and waking symptoms; subjective-objective discrepancy

Sleep characteristics; diagnosis; treatment response

Immediate early gene expression(cells, structures)

Cano, J Neurosci, 2008; 28:10167-84

Measuring sleep in animals

Tracer studies (neural pathways, circuits)

Low Low

Low HighHighHigh

HighHigh

Activity and quiescence (behavior)

Liu, eNeuro 2, 2015

Electrophysiological recordings ( whole brain, structures, cells)

EEG ECoG FP, Unit Intra-Spikes cellular

EEG = electroencephalography. ECoG = Electrocorticography. FP = Extracellular field potential

Measuring sleep in humans

Imaging(Circuits)

Self-Report(Experiential)

PSG(Electrophysiological)

Actigraphy(Behavioral)

3 neurobehavioral states

Non-Rapid Eye Movement (NREM) Sleep

• EEG: High-amplitude, slow frequencies; “synchronized;” sleep spindles

• Behavior: Minimal• Systemic physiology: “slow,”

stable, quiet• Awareness, arousal: Low

Rapid Eye Movement (REM) Sleep

• EEG: Low-amplitude, mixed frequency; “desynchronized”

• Behavior: Skeletal muscle paralysis, rapid eye movements

• Systemic physiology: High variability, activated

• Awareness, arousal: Dreaming

Wakefulness

• EEG: Low-amplitude, fast frequency; “desynchronized”

• Behavior: Full repertoire• Systemic physiology: Reactive

to circumstances• Awareness, arousal: Ranges

from alert to drowsy

Where in the brain is sleep? Transection experiments

Frontal cortex

Thalamus

Midbrain

Pons

Medulla

Hypothalamus

Cingulate cortex

Brainstem

Diencephalon

Neocortex

Note: These experiments were conducted in laboratory animals. Results are depicted in relation to a human brain.

Where in the brain is sleep? Transection experiments

Cerveau isolé

▪ Isolates brainstem from diencephalon, cortex

▪ Cortex: Slow waves and EEG spindles (sleep)

▪ Conclusion: Brainstem necessary for EEG wakefulness

Frontal cortex

Thalamus

Midbrain

Pons

Medulla

Hypothalamus

Cingulate cortex

Brainstem

Diencephalon

Neocortex

McGinty & Szymusiak, Principles and Practice of Sleep Medicine, 6th edition, 2016; Chapter 7.

Where in the brain is sleep? Transection experiments

Diencephalic preparation

▪Neocortex, striatum removed

▪ Behavioral waking; quiet, NREM-like state; REM-like state

▪ Some EEG features of NREM sleep absent (spindles, slow waves)

▪ Conclusion: Cortex not required for behavioral sleep-wake states

Frontal cortex

Thalamus

Midbrain

Pons

Medulla

Hypothalamus

Cingulate cortex

Brainstem

Diencephalon

Neocortex

McGinty & Szymusiak, Principles and Practice of Sleep Medicine, 6th edition, 2016; Chapter 7.

Where in the brain is sleep? Transection experiments

Midpontinetransection

▪ Isolates lower pons and medulla from midbrain, diencephalon, cortex

▪ Cortex: Activated EEG, some episodes of slow activity

▪ Conclusion: Mid-pons, midbrain necessary for EEG wakefulness and wake-like state

Frontal cortex

Thalamus

Midbrain

Pons

Medulla

Hypothalamus

Cingulate cortex

Brainstem

Diencephalon

Neocortex

McGinty & Szymusiak, Principles and Practice of Sleep Medicine, 6th edition, 2016; Chapter 7.

MnPN

“Reticular formation”

Wake and sleep-promoting structures in the brain

Wake-Promoting Systems Sleep-Promoting Systems

Saper, Nature, 2005; 437: 1257-63

StructuresBF= basal forebrainLC= locus coeruleusLDT= laterodorsal tegmental nucleiMnPN= Median preoptic nucleusvPAG = Periaqueductal grayPPT= pendunculopontine tegmental nuclei TMN= tuberomammillary nucleusVLPO= ventrolateral preoptic nucleus

“Encephalitis lethargica”

Lesions resulting in somnolence (90%)

Lesions resulting in insomnia (10%)

Von Economo, 1926 Triarhou, Brain Res Bull 2006; 69: 244-258

During the 1918-1926 influenza pandemic, some patients developed “encephalitis lethargica,” characterized by severe sleepiness and later, symptoms of Parkinson’s disease. A smaller percentage developed severe insomnia.

The “flip-flop” sleep switch: How brain structures generate wakefulness and sleep

Saper, Nature 2005; 437:1257-63

Wakefulness

MnPN

NREM Sleep

MnPN

REM sleep: Reciprocal inhibition control

España and Scammell, SLEEP, 2011; 34: 845-58. Pace-Schott and Hobson, Nat Rev Neurosci, 2002; 3:591-605

5-HT = serotonin; Ach = acetylcholine; BRF = brainstem reticular formation; DR = dorsal raphe; Glu = glutamate; LC = locus coeruleus; LDT/PPT = laterodorsal and pedunculopontine nuclei; LPT = lateral pontine tegmentum; MCH = melanin concentrating hormone; NA = norepinephrine; SLD =sublaterodorsal nucleus; TMN = tuberomammillary nucleus; vlPAG= ventrolateral periaqueductal gray;

Key concept: “REM-on” cells stimulate their own activity, as well as the activity of “REM-off” cells. “REM-off” cells inhibit their own activity, as well as activity of “REM-on” cells. This leads to a self-sustaining cycle of NREM and REM sleep.

How long you’ve been awake

What regulates sleep? The hourglass, the clock, and the alarm

Sle

ep D

rive

→

Sle

ep P

rop

ensi

ty →

Aro

usa

l L

evel

→

Time of day

Level of arousal

Homeostatic sleep drive

Circadian sleep propensity

Psychophysiological arousal

Sleep-Wake State Switching System

VLPO, MnPO“Sleep Switch”

LHA“Wake Stabilizer”

Brainstem-HypothalamicArousal System

LC, Raphe, LDT/PPT, TMN;VTA

HomeostaticSleep Drive

CircadianTiming System

Sleep-WakeRegulatory System

Thalamus

Dorsal (Cognitive)System

Ventral (Affective)System

Cognitive-Affective System

Solid arrows indicate direct anatomic or physiologic pathways. Dotted arrows indicate indirect pathways. VLPO = Ventrolateral preopticarea. LHA = Lateral hypothalamus peri-fornical area. LC = locus coeruleus. LDT = Laterodorsal pontine tegmentum. PPT = Pedunculopontine tegmentum. TMN = Tuberomamillary nucleus of the posterior hypothalamus; VTA = Ventral Tegmental Area.

Buysse et al., Drug Discovery Today: Disease Models, 2011; 8:129-137

“Circuit” model of sleep-wake regulation

Brain control of wakefulness and NREM sleep: Neurochemical

Wake-Promoting Systems Sleep-Promoting Systems

Saper, Nature, 2005; 437: 1257-63

StructuresBF= basal forebrainLC= locus coeruleusLDT= laterodorsal tegmental nucleiMnPN= Median preoptic nucleusvPAG = Periaqueductal grayPPT= pendunculopontine tegmental nuclei TMN= tuberomammillary nucleusVLPO= ventrolateral preoptic nucleus

Neurotransmitters5-HT = serotoninACh= AcetylcholineDA = DopamineGABA = Gamma-aminobutyric acidGal= galaninHIST= histamineMCH = Melanin Concentrating HormoneNA= noradrenalineORX = Orexin

Yellow = Mostly wake-promotingBlue = Mostly sleep-promoting

MnPN

Activity profiles of neurotransmitter systems across wakefulness, NREM, and REM sleep

Neurotransmitter Wakefulness NREM Sleep REM Sleep

Acetylcholine (Ach) −

Monoamines: Serotonin (5-HT), Norepinephrine (NE, NA), Histamine (HA)

−

Orexin (Hypocretin) − −

Melanocyte Concentrating Hormone (MCH) − −

Gamma-aminobutyric acid (GABA) −

Neuronal activity: = rapid firing rate; = slower firing rate; − = little or no firing

España and Scammell, SLEEP, 2011; 34: 845-58. McGinty & Szymusiak, Principles and Practice of Sleep Medicine, 6th edition, 2016; Chapter 7.

Adenosine, an inhibitory neuromodulator, accumulates in the basal forebrain and brainstem as a function of increasing wake duration, and decreases during subsequent sleep. Thus, adenosine may be part of the “sleep homeostat.” Adenosine inhibits wake-active neurons. Caffeine is an adenosine receptor antagonist.

Medication effects on neurotransmitters explain their sleep-wake effects

España and Scammell, SLEEP, 2011; 34: 845-58.

Drug Type Examples Pharmacologic, Biological effect

Sleep Effects

Stimulants Amphetamine, modafinil methylphenidate

dopamine and norepinephrine

Increased wakefulness

Benzodiazepine receptor agonists

Diazepam, lorazepam, zolpidem

GABA signaling Increased NREM sleep

Orexin receptor antagonists

Suvorexant, lamborexant orexin signaling to arousal centers

Increased NREM sleep

Selective serotonin reuptake inhibitors (SSRI)

Fluoxetine, sertraline, citalopram

extracellular serotonin Decreased REM sleep, increased wakefulness

Heterocyclic antidepressants

Amitriptyline, doxepin, trazodone

histamine signaling; extracellular serotonin and norepinephrine

Increased NREM, decreased REM sleep

First-generation antihistamines

Diphenhydramine, hydroxyzine

histamine signaling Increased NREM

Typical antipsychotics

Haloperidol, chlorpromazine

dopamine signaling Increased NREM

(GABA)

Global and local sleep

Structure A

Structure B

Humoral

Electrical

NeuronNeuronalColumn

NeuronalAssemblies

Circuits,Networks

Use-dependent ↑ in sleep-regulatory substances(Adenosine, NO, TNF, IL-1)

Sleep as an “emergent process”

Wake Promoting Systems Sleep Promoting Systems

Sleep-wake as bi-stable, global stateSaper, Nature, 2005; 437:1257-63

Sleep as a local, use-dependent stateKrueger, Nat Rev Neurosci 2008; 9:910-919

NO = Nitric oxideTNG = Tumor Necrosis Factor IL-1 = Interleukin-1

Global sleep, local sleep

Sleep-Wake as Bi-Stable States1

Sleep

Wake

Wake

Sleep

1Saper, Nature, 2005; 437:1257-63. 2Krueger, Nat Rev Neurosci 2008; 9:910-919 3Buysse, Drug Disc Today: Dis Mod, 2011; 8:129-137

Sleep-Wake as Local, Use-Dependent2

Sleep

Wake

Wake

SleepSleep

Wake

Wake

Sleep

Sleep

Wake

Wake

Sleep

Sleep

Wake

Wake

Sleep

Sleep

Wake

Functional neuroimaging of human sleep

▪ EEG monitoring of sleep-wake state

▪ Injection of radioactive tracer during desired state ▪

15O-H2O for blood flow

▪18F-fluoro-deoxyglucose for regional glucose metabolism

▪ Imaging of emission pattern of radiotracer

Functional imaging: NREM and REM sleep

Nofzinger, Psychiatry Res Neuroimag, 1999. Brain, 2002; 125: 1105-1115. Maquet, J Sleep Res, 2000; 9:207-31. Schwartz and Maquet, Trends in Cog Sci, 2002; 6: 23-30

Wake > NREM regional metabolism, blood flow▪ Dorsolateral prefrontal cortex▪ Inferior parietal cortex▪ Precuneus, Posterior cingulate▪ Medial frontal-anterior cingulate cortex▪ Thalamus

Regional glucose relative metabolism Wake > NREM Regional blood flow during REM (schematic)

Increases▪ Amygdala▪ Hippocampus▪ Anterior cingulate▪ Occipital cortex▪ Motor cortex▪ Thalamus▪ Basal forebrain▪ Pontine tegmentum

Decreases▪ Frontal cortex▪ Parietal cortex▪ Posterior cingulate

Regional glucose metabolism in wake vs. NREM sleep: Insomnia vs. good sleepers

Kay, Buysse et al., 2016; SLEEP 39: 1779-1794

How we sleep: Cells to circuits to physiology

Take Home Points

Wakefulness, NREM sleep, and REM sleep are distinct neurobiological and neurobehavioral states

Wakefulness, NREM sleep, and REM sleep are generated by distributed brain regions, primarily in the brainstem and hypothalamus

The regulation of wakefulness, NREM sleep, and REM sleep relies on interactions between these brain regions, and on homeostatic and circadian factors

No neurotransmitter is exclusively responsible for wakefulness, NREM sleep and REM sleep, but medication effects on these neurotransmitters helps us understand their sleep-wake effects

Sleep-like and wake-like states are also intrinsic to individual neurons

Functional neuroimaging studies can be used to characterize regional variations in sleep and to investigate the effects of sleep manipulations and disorders in humans