PSYC 280 UNIT 8: sleep, rhythyms, compact

What are biological rhythms

Any biological process (including behavior) that repeats itself at regular intervals. Manifest at all levels of biological organization and extend across a wide frequency (cycles/unit time) spectrum.

How are biological rhythms classified

rhythms are about a day long

• Ultradian (<< 24h)

• Circadian (24 h)

• Infradian (>>24 h)

• Diurnal, nocturnal, crepuscular

What is a circadian rhythm

Endogenous clock

Keeping time for animals, in:

• constant conditions

• Free running rhythm

• Cues

• Periods (time of one cycle)

• Resetting (phase shifts, entrainment, zeitgeber/ time giver/ sun)

What is the suprachiasmatic nucleus (SCN)

The part most that most likely serves as a clock, due to:

• Lesions eliminate various rhythms

• SCN itself shows rhythmic metabolic activity

• Rhythms in slices

• Rhythms in SCN cell cultures

• In vivo recordings and autoradiography / IEGs

Tau mutants

Evidence of SCN being the master clock. identified in a colony of hamsters

• unusually short period (about 20 hours)

• Experiment: Circadian period recorded in

normal hamster, SCN ablation = arrhythmic, Transplant of cells from tau mutant donor, Eventually, host expresses

donors rhythm

Retinohypothalamic Tract

Direct projection of retinal ganglion cells to SCN via optic

nerve. Their ganglion cells contain specialized photopigment, melanopsin. Essentially, stuff that regulates rhythm ex. Sensitivity to light.

Molecular foundations of the clock

Regulation of gene transcription, via

negative feedback loops, in the SCN, produces rhythms

• From work with Drosophila – mutation in Per (for Period) causes abnormally short or long activity periods in flies

Shorter rhythms

• Ultradian rhythms- occur more than once per day

• Periods last from several minutes to several hours

• Examples include- eating, bouts of activity, hormone secretion, protein incorporation, daydreaming (90 minute

cycle!), etc.

• Superimposed on top of circadian rhythms

• Multiple oscillators? Perhaps ‘slaved’ to SCN

Longer rhythms

Sometimes called infradian (less than once per day)

rhythms

• One well known infradian rhythm is human female

reproductive cycle- about 28 days in length – ‘circalunar’

• Annual rhythms and seasonal affective disorder (SAD)

o Akin to hibernation in humans?

• Lesion of SCN often does not affect these cycles- another

oscillator independent of the SCN??

Circannual rhythms

• ‘Seasonal cycles’- about a year

• Examples - Metabolism, Reproduction, Migration

• Hamsters (Siberian) – gonadal regression/ recrudescence, and change in pelage

• Function:

• Winter survival

• Coordinated reproduction as antipredator strategy

Type I (Endogenous/Exogenous Control)

Due to photoperiodism (melatonin duration), lesions

to the SCN prevents these cycles

Type II (True Endogenous Control)

• have secondary pacemakers/ oscillators

• SCN lesions do not affect these cycles, indicating

  that there must be secondary pacemakers/oscillators

• Example: Hibernation in ground squirrels

What is the definition of sleep

• A Circadian distribution of activity

• Prolonged phase of inactivity

• Raised threshold to environmental stimuli during

Inactivity

• Species specific posture of inactivity

• All animals show this

Sleeping- comparative data

• All mammals display REM and SWS- two exceptions

dolphins (SWS only, and only one hemi at a time!) and

echidnas (no obvious forebrain LVF-like activity during

sleep)

• reptiles don’t, birds do

• Vertebrates differ in patterns and types of sleep

Human sleep

• regulated by light

• Humans (like hamsters) free run- showed activity period of about 25hrs

• changes without day/night cycle, ex. Dark cave

Human sleep stages

• Measured via electroencephalogram (EEG) with EOG and EMG

• REM sleep and slow wave sleep (SWS)

• SWS divided into 3 characteristic stages:

Waking, stage 1, stage 2, stage 3 SWS, REM

Dreaming and sleep

• occur during REM sleep (70-90% of subjects)

• lots of visual imagery

• Characteristic cortical LVF activity looks strikingly similar

to awake EEG

• Nightmares- REM, Night terrors- sudden arousal from stages 3-4 SWS, intense fear and autonomic activation

How do sleep patterns change across life span

• Circadian pattern of sleep evident at 16 weeks in babies- but the sleep length is shorter than that of adults.

• Babies spend a lot of time in REM sleep

• Maturation of the nervous system?

• Consolidation of memories

Sleep in the elderly

Stages 3 and 4 decline in old age

• Eliminated by age 90

• May relate to diminished cognitive abilities

• Inability to ‘maintain’ sleep once achieved

What are the effects of sleep deprivation

• Sleepiness

• Bizarre behavior- hallucinations in some subjects deprived of approximately 8.5 days

• Irritability, difficulty concentrating, disorientation

• cognitive deficits on spatial tasks, and reduced volume of temporal lobe (stress)

• Total sleep deprivation in mammals leads to death- due to hypothermia and immune system dysfunction

Sleep recovery

• After 11 days of sleep deprivation, case study subject slept for over 13 hours the first night.

• Stage 4 increased at expense of stage 2, but never

“catches up” to the sleep deficit.

• REM increases in intensity and recovers by night 2

What is the function of sleep

• Energy conservation

• Predation avoidance

• Body restoration

• Consolidation of memory

Consolidation of memory

• replaying’ days activities and ‘consolidating’

  memories for these experiences

• LVF cortical EEG activity is increased during REM sleep- neurons are active during sleep

Neural systems underlying sleep

• Sleep is actively stimulated and regulated by brain

• 4 regions are important

  1) Forebrain region- displays SWS by itself

  2) Brainstem region- activates forebrain region into

  wakefulness

  3) Pontine region- triggers REM

  4) Hypothalamic system- regulates the other 3 systems

  to determine sleep or wakefulness

Encephale isole

transection between medulla and spinal cord, animal continues to show sleep-wake states

Cerveau isole

transection in the midbrain, and the forebrain remains in SWS, forever.

Basal forebrain

ventral lobe and anterior

hypothalamus lesions abolish SWS; stimulation here

induces SWS

The basal forebrain

• Neurons become active during SWS onset- in fact, the Basal forebrain actively imposes SWS on the brain

• Inhibited by noradrenergic stimulation

• Uses GABA to suppress tuberomammillary nucleus in hypothalamus; shuts down activity

Reticular formation in the brain stem

• Wakes up cortex

• Axons widely dispersed; projects to entire forebrain

• Electrical stimulation of reticular formation rapidly wakes animals up

• Lesions in the RF produce persistent Sleep

The pons

• Triggers REM sleep

• Lesions eliminate REM sleep

• Some neurons here only seem to be active during REM sleep

• Causes muscle atonia- loss of muscle tone- though the inhibitory neurotransmitter GABA- causes IPSPs in spinal motoneurons

• flaccid muscles

The anterior hypothalamus

• Narcolepsy: frequent, uncontrolled, and intense attacks of sleep brought on by emotional experiences

• Can last from minutes to hours; involves loss of muscle tone (cataplexy) and instant REM bouts

• Hypocretin (or orexin) is crucial – KO mice and dogs

display signs of narcolepsy

Hypocretin and narcolepsy

May function to keep sleep at bay and prevent transition from wakefulness into REM sleep

• Hypothalmus projections to:

§ pons,

§ basal forebrain,

§ reticular formation,

§ tuberomammillary nucleus

Somnambulism

• sleep walking; more common in children; amnesia for the experience; occur in stages 3 and 4

• Occasionally seen in criminal cases (murder and rape)

REM sleep disorder

organized sleep walking; fighting a foe, eating a meal,

acting like an animal;

§ may be acting out of a dream - people often

report dreams on waking

Insomnia

• inability to fall asleep

• 15-30% of adult pop’n

• more prevalent in females, smokers, alcoholics and

  caffeine users

  • Multiple causes- medical condition, psychiatric or

  neurological condition, first night effect, shift work

  • Sleep onset insomnia, vs. Sleep maintenance insomia

  • Sleep apnea- breathing ceases