Neurobiology of Sleep Subimal Datta Sleep Research Laboratory Department of Psychiatry Boston University School of Medicine, Boston, MA
Jan 20, 2016
Neurobiology of Sleep
Subimal DattaSleep Research LaboratoryDepartment of Psychiatry
Boston University School of Medicine, Boston, MA
25th Birthday
9 Years of Sleep
2.5 Years of
Dreaming
Happy Birthday!
Sleep Medicine• Sleep ranks among the 3 most important
considerations in maintaining good health
– Accompanied by good nutrition and stress management
• 62% of US population experiences sleep problems
• 80% of US adults have NEVER discussed sleep problems with their physician
• Societal bias equates sleepiness with laziness
Objectives of this Lecture
To describe methods for the objective identification of different stages of sleep
To describe the patterns of sleep, and factors influencing those patterns
To describe circadian and homeostatic aspects of sleep
To describe neuronal substrates of sleep
Definition and QualitativeDescription of Sleep
• Sleep is a reversible behavioral state of perceptual disengagement from, and unresponsiveness to, the environment.
• Species-specific postural recumbenceSpecies-specific postural recumbence• Behavioral quiescenceBehavioral quiescence• Elevated arousal thresholdElevated arousal threshold• Rapid arousal after moderate stimulationRapid arousal after moderate stimulation• Perceptual disengagement from environmentPerceptual disengagement from environment• DreamsDreams
• Other behaviors: sleep walking, sleep talking, tooth Other behaviors: sleep walking, sleep talking, tooth grinding, and some physical activities may also bee seen grinding, and some physical activities may also bee seen during sleep.during sleep.
Sleep is a special activity of the brain.
Stages of Sleep
• Non-rapid Eye Movement (NREM) Sleep
-Stage 1
-Stage 2
-Stage 3
-Stage 4
• Rapid Eye Movement (REM) Sleep
-Phasic
-Tonic
Polysomnography (PSG)
Standard Physiological VariablesStandard Physiological Variables• Electroencephalogram (EEG)Electroencephalogram (EEG)• Electrooculogram (EOG) Electrooculogram (EOG) • Electromyogram (EMG)Electromyogram (EMG)
Additional VariablesAdditional Variables
• Respiratory MovementsRespiratory Movements• Blood Oxygen SaturationBlood Oxygen Saturation• Heart Rate Heart Rate • Leg MovementsLeg Movements
Electroencephalogram(EEG)Electroencephalogram(EEG)
Reflects local potentials at the level of Reflects local potentials at the level of cerebral cortex, specifically a summary of cerebral cortex, specifically a summary of local synaptic potentials on cortical local synaptic potentials on cortical pyramidal neurons.pyramidal neurons.
Type, location and mutual synchronization Type, location and mutual synchronization of these potentials is reflected in different of these potentials is reflected in different shape, amplitude and frequency of shape, amplitude and frequency of recorded brain waves.recorded brain waves.
Electrode Placement
A1 A2
C3
EEGEEG
Alpha 8-13 Hz
Beta > 13 Hz
Theta 4-7 Hz
DeltaDelta < 4 Hz < 4 Hz
FREQUENCY AMPLITUDEAMPLITUDE
< 5 < 5 VV
5-15 5-15 VV
10-50 10-50 VV
> 50 > 50 VV
Sharp wave
K Complex
EEG
EEG
EEG
EEG
EEG
EEG
TypicalEEG signs for the identification of different stages of sleep
Electromyogram (EMG)
• Three electrodes are placed beneath the chin, overlying Mentalis/submentalis muscles.
• Sometime, the Anterior tibialis EMG is important to evaluate patients with PLM disorder.
Awake
NREMSleep
REMSleep
Electrooculogram (EOG)Electrooculogram (EOG)
retinaretina++ corneacornea
EOG is measured based on corneo-retinal EOG is measured based on corneo-retinal potential. As eyeballs move, the electrical potential potential. As eyeballs move, the electrical potential field changes with reference to electrodes.field changes with reference to electrodes.
Wakefulness and Transition toNon-REM Sleep
Non-REM Sleep: Stage 1
NREM Sleep: Stages 2-4
Stage 3
Stage 4
Stage 2
Outline of Standard Criteria for Scoring NREM sleep Stages
Stage 1EEG: Relatively low voltage, mixed frequency; may be theta (3-7 cps) activity with greater amplitude; Vertex sharp waves; Synchronous high-voltage theta bursts in childrenEMG: Tonic activity, may be slight decrease from wakingEOG: Slow eye movements
Stage 2EEG: Sleep spindles (waxing and waning at 12-14 cps, ≥ 0.5 sec); K complex (negative sharp wave followed immediately by slower positive components; maximal in vertex; spontaneous or in response to sound)
EMG: Tonic activity, low level
EOG: Occasionally slow eye movements near sleep onset
Stage 3EEG: ≥ 20 ≤ 50% high amplitude (> 75 V), slow frequency (≤ 2 cps); maximal in the frontalEMG: Tonic activity, low levelEOG: None, picks up EEG
Stage 4EEG: >50% high amplitude, slow frequencyEMG: Tonic activity, low levelEOG: None, picks up EEG
Orthodox of NREM SleepDEEPER SLEEPDEEPER SLEEP
GREATER SYNCHRONYGREATER SYNCHRONY
SLEEP STAGESLEEP STAGE
11
22
33
44
AWAKEAWAKE
Rapid Eye Movement (REM) SleepHuman
Rat
Signs of REM Sleep
• EOG: Rapid eye movements (REMs)EOG: Rapid eye movements (REMs)
• EEG: High frequency low amplitude EEG; EEG: High frequency low amplitude EEG; Sawtooth waves; theta activity; PGO/P-wavesSawtooth waves; theta activity; PGO/P-waves
• EMG: Antigravity or postural muscles are EMG: Antigravity or postural muscles are paralyzedparalyzed
• Muscle jerksMuscle jerks
• Penile/clitoral tumesencePenile/clitoral tumesence
Signs of REM Sleep• Thermoregulation is absent (poikilothermia)Thermoregulation is absent (poikilothermia)
• Irregular breathing, including brief Irregular breathing, including brief hypopneas and apneashypopneas and apneas
• Unstable cardiac system (variable heart rate Unstable cardiac system (variable heart rate and blood pressure). Indeed some speculate and blood pressure). Indeed some speculate that the phasic excitation of the cardiac that the phasic excitation of the cardiac system during REM may trigger heart system during REM may trigger heart attacksattacks
• DreamDream
The Progression of Sleep Stages Across a Single Night
24 1 2 3 4 5 6 7
Wake
S1
S2
S3
S4
REMMov.
Time in Hour
Sle
ep-W
ake
Sta
ges
Generalizations About Sleep in the Normal Young Adult Human
• Sleep is entered through NREM.
• NREM sleep and REM sleep alternate with a period near 90 min.
• Slow wave sleep predominates in the first third of the night and is linked to the initiation of sleep.
• REM sleep predominates in the last third of the night and is linked to the circadian rhythm of body temperature.
- Continuation• Wakefulness within sleep usually accounts
for less than 5 percent of the night.
• Stage 1 sleep generally comprises about 2 to 5 percent of sleep.
• Stage 2 sleep generally comprises about 45 to 55 percent of sleep.
• Stage 3 sleep generally comprises about 3 to 8 percent of sleep.
- Continuation
• Stage 4 sleep generally comprises about 10 to 15 percent of sleep.
• NREM sleep, is therefore, is usually 75 to 80 percent of total sleep.
• REM sleep is usually 20 to 25 percent of total sleep, occurring in four to six discrete episodes.
How do these wake and sleep stages play out over the night and day?
• Circadian Rhythm (24 hours)
• Sleep Homeostasis
Circadian Rhythm of Sleep
Days1 2 3 4
Clock in the Brain• Overwhelming evidence indicates that the
suprachiasmatic nucleus (SCN), a paired structure located in the anterior hypo-thalamus contains a circadian pacemaker.
• Circadian rhythms are abolished with complete lesions of the SCN.
• SCN transplants into the third ventricle and hypothalamus restores rhythmicity in previously arrhythmic animals.
CIRCADIAN BODY RHYTHMSCIRCADIAN BODY RHYTHMS
SCN
MELATONINMELATONIN NIGHT
Sleep HomeostasisSleep Homeostasis
• Sleepiness increases in proportion to leepiness increases in proportion to prior awake timeprior awake time
• There is a “pressure” to keep awake There is a “pressure” to keep awake and sleep time balancedand sleep time balanced
• There is a need for recovery sleep There is a need for recovery sleep after sleep deprivationafter sleep deprivation
Age-related Changes in Sleep PatternAge-related Changes in Sleep Pattern
Age-related Changes in Total Amount of Daily Sleep
4025
20
18.915 3.8
Sleep in ElderlySleep in Elderly
Earlier sleep onsetEarlier sleep onset
Early morning awakeningsEarly morning awakenings
Daytime sleepinessDaytime sleepiness
Loss of delta sleepLoss of delta sleep
Reduced REMs and dream recallReduced REMs and dream recall
CEREBRAL CORTEXCEREBRAL CORTEX
THALAMUSTHALAMUS
PONSPONS
SPINAL CORDSPINAL CORD
Brain AreasBrain Areas ● ● Hypothalamus Hypothalamus ● ● Basal Forebrain Basal Forebrain ● ● Brainstem:PonsBrainstem:Pons
NeurotransmittersNeurotransmitters● ● AchAch●● GlutamateGlutamate● ● GABAGABA●● HistamineHistamine● ● NENE●● 5-HT5-HT● ● PeptidesPeptides●● NONO
Mechanisms of SWS Generation
EEG
Cortex
Hpc
Cerebellum
Midbrain
Pons
Medulla
Thalamus
AC
OX
R scp
SolPOA TMN
Brainstem Network for REM Sleep Sign Generation
Thank You!