Physiology of sleep and dreaming

The sleep cycle

Dreaming

Why do we sleep?

Sleep and consciousness

Diurnal rhythms1 degree in the early evening higherAdrenocortical H.in the morning higher

Sleep –wake cycle

• When Awake: able to perform all activities for individual and species survival

• When sleep: is not aware and not able to ….

Assesment of sleep states

• 1- behavioral analysis• 1- EEG analysis• EEG : represent the summated

activity of millions of cortical neurons.IPSPs and EPSPs and passive spread of electrical activity is the basis of EEG

The sleep cycle

• Electronic recording: EEG, EOG, EMG• EEG patterns divide sleep into four stages:

– 1: waves, 8 - 12 Hz, low amplitude, moderate frequency, similar to drowsy wakefulness

– 2: slower frequency, higher amplitude, plus• K complexes• Sleep spindles

– 3: waves appear, 1-2 Hz, large amplitude– 4: Dominated by waves

REM sleep phenomena

• Stage 1 EEG: Paradoxical sleep• EOG (and corneal bulge) show frequent

eye movements, as if scanning a visual field.

• EMG shows loss of muscle tonus due to downward inhibition of motor neurons, although muscles moving hands and feet may twitch.

• Many brain structures function as if awake.

More REM phenomena• SNS is partially activated: Increases blood

pressure, respiration, and heart rate.• Genital response• Narrative dreaming

– CBF is high to visual cortex, low to inferior frontal cortex (Madsen, 1991)

– Eye movements match dream events– One EEG waveform is unique to REM and

wakeful scanning

Dream research

• External stimuli may be incorporated into a dream.

• Dream events happen in real time.• Sleep-walking and talking are non-

REM.

Interpretation of dreams

• Manifest content is symbolic of latent desires (Freud)

• Activation-synthesis theory: cf. incorporation of external events into dreams.

• Lucid dreams: Have you had one?

Why do we sleep?

• Restoration, recuperation or repair– Waking life disrupts homeostasis

• Protection with the circadian cycle • Circadian synthesis

Who sleeps?

• Mammals and birds– Opossums, sloths, bats: 19-20 hours daily– Cats, dogs, rodents: 12-15 hours daily– Ruminant herbivores: 2-3 hours daily

• Reptiles, amphibians, fish, and insects have cycles of inactivity

• Note that sleep time does not correlate with waking activity levels, but does relate to waking vulnerability.

SWS

تغييرات مراحل خواب با افزايش سن

Sleep during infancy

• Neonate can sleep 18 hours during a 24 hour period

• During the first year of life the sleep period may be reduced to 12 hours

• Infant may have up to 50% of REM SLEEP or more , while adults have 20%

• Sleep cycles are shorter than in the adult, 50-60 min

• Cycles can start with REM sleep. REM is controlled by a more primitive center, brainsteam.

Slow Wave Sleep REM/Paradoxical Sleep

EEG Large Amplitude Low Amplitude (cf waking)

Slow Waves ~ 1 Hz (but theta rhythm in hippocampus)

MUSCLES Reduced tone Total relaxation (e.g. in postural & neck muscles)

SPINAL Some reduction Strong descending inhibitionREFLEXES of motoneurons

AROUSAL to ‘significant’ stimuli Raised threshold (deep sleep)but often waking from REM

PHASIC Muscle twitches Sudden eye movements (REM)EVENTS Sudden CNS discharges

REPORTS ‘dreams’ 0-50% ‘dreams’ 80%-90% ON WAKING & ‘thinking’

Slow Wave Sleep REM/Paradoxical Sleep……ctd….

REPORTS ‘dreams’ 0-50% ‘dreams’ 80%-90% ON WAKING & ‘thinking’

% of SLEEP 60% - 85% ~40% infants~20% most of life~15% old age

WHEN Initially and in cycles Not initially (except narcoleptics)~ 90 min cycle

EMG و EEGبررسي امواج در مراحل مختلف خواب

نحوه قرارگيري الكترودها EEGروي سر جهت ثبت

الگوي جريان الكتريكي جهت ايجاد پتانسيل پس

سيناپسي تحريكي

نحوه تغيير پوالريته امواج EEG

توليد پتانسيل عمل و كانالهايكلسيمي دريچه ار ولتاژي

تاالموس

ارتباط سطح فعاليت مغز و فركانس متوسط امواج

مغزي

Circadian rhythms

• Zeitgebers and the SCN• Free-running rhythms and the 25-

hour period• Internal desynchronization: free-

running body temperature cycle and sleep-wake cycle may desynchronize.

Resynchronization

• Jet lag and shift work• Phase shift: Delay is better than advance

– Morning melatonin phase-delays– Afternoon melatonin phase-advances– Evening melatonin is ineffective– Bright light exposure has the opposite effects

• Strengthen zeitgebers like light and activity early in the new waking period

Neural control of sleep

• Is sleep a passive process?– The cerveau isole’ of Bremer (1936)– The encephale isole’ and the RAS– Partial transections leaving the RAS intact

• Ventrolateral Preoptic Area (VPA) triggers sleepiness and slow-wave sleep

• Warming the basal forebrain induces slow-wave sleep

• VPA receives input from thermoreceptors

More neural control

• PGO waves in the EEG from implanted electrodes

• Executive in the dorsolateral pons, called the peribrachial area.

• Kainic acid lesions of peribrachial area reduce REM sleep

• Carbachol, an ACh agonist, in ventral pons (medial pontine reticular formation) triggers REM phenomena.

REMطرح كنترل خواب

مدل ساختاري و ديناميك REMفعاليت مغز در خواب

The Ascending Arousal System

Von Economo, C. J. Nerv. Ment. Dis. 71, 249–259 (1930)

Nuclei of certain known chemicalneuro-modulatory systems• AcetylCholine: Tegmentum [PGO]• Noradrenaline: Locus Coeruleus [Arousal]• 5HT (serotonin): Raphe [Arousal, SWS]

Arousal and Neuro-modulatory Systems

Thalamus

Diffuse projection from RETICULAR ACTIVATING SYSTEM (R.A.S.) -> arousal

‘Specific’ sensory signals to thalamus and cortex

‘Non-specific’ collaterals of sensory axons go to RETICULAR ACTIVATING SYSTEM (R.A.S.)

The Ascending Arousal System

Moruzzi, G. & Magoun, H.W. Electroencephalogr. Clin. Neurol. 1, 455–473 (1949)

Known neurotransmitters originating from well-defined cell groups:

• LC: Locus Coeruleus

• BF: Basal Forebrain

• LH: Lateral Hypothalamus

• TMN: Tuberomamillary Nuclei

• LDT/PPT: Pedunculopontine / Laterodorsal Tegmental Nuclei

NB: Link to von Economo’s work

• REM is mediated by brainstem, through a cholinergic system

• Non-REM is mediated by the locus coeruleus of the brainstem and the messenger is adrenaline

• There may be a homeostatic load through the day that makes the need for rest imperative

• There are light/darkness cues perceived in the suprachiasmatic nucleous (hypothalamus)