2017-02-24 10:19:34

Prelude

Today's Topics

  • Biological rhythms
  • To sleep, perchance to dream…

I got rhythm…

  • Rhythms operate at multiple time scales
  • Ultradian (> 1x day)
    • 90-110 min cycles of heart rate, day dreaming
  • Circadian
    • Diurnal vs. noctural

Biological rhythms

  • Infradian (< 1x day)
    • Menstrual or estrus cycles
    • Circannual

Factors influencing rhythms

  • Endogenous factors
    • Internal oscillator or “clock”
    • “Free-running”
  • Exogenous factors
    • “Zeitgeber” or “time-givers” reset clock (entrainment)
    • Or, independent of clock

Mechanisms of biological timekeeping

  • Endogenous
    • Cellular, neural oscillators
    • Genetic, hormonal variations
  • Exogenous (external to organism)
    • Light
    • Temperature
    • Sound

Physiological mechanisms

  • Pineal gland & melatonin
  • Suprachiasmatic nucleus (SCN) of the hypothalamus

SCN Figure

Pineal gland & melatonin

  • Pineal gland
    • Input from SCN via sympathetic NS
  • Melatonin
    • Secretion peaks at bedtime
    • Controls hibernation in some species

Pineal gland figure

Sleep

  • The structure of sleep
  • The neuroscience of sleep
  • Why do we sleep?

Structure of sleep

  • cyclic, has phases
  • 90-110 min cycles

Sleep structure figure

Sleep phases

Neuroscience of sleep

  • Electroencephalogram (EEG) evidence
  • EEG frequency bands
    • Delta: 1-4 Hz
    • Theta: 4-8 Hz
    • Alpha: 8-12 Hz
    • Beta: 13-30 Hz
    • Gamma: >30-50 Hz

Sleep stages and EEG

Awake state

  • EEG
    • Low amplitude
    • High frequency
  • Beta band: attentive state
  • Alpha band: quiet rest

Stage 1 and 2

  • Stage 1
    • Drowsy, don’t feel asleep
    • Theta wave
  • Stage 2
    • Sleep spindles (12-14 Hz bursts)
    • K complexes

Slow-wave sleep (Stages 3 & 4)

  • EEG
    • Synchronized
    • Delta wave (1-4 Hz)
  • Groggy if awoken
  • Rarely report vivid dreaming

Sleep EEG figure

Rapid Eye Movement (REM) Sleep

  • ~ 20% of sleep
  • Desynchronized EEG
    • Similar to Stage 1

More on REM sleep

  • Muscular paralysis except eyes
  • Vivid dream state
  • Cortex activity > awake state
  • “Paradoxical” sleep

REM sleep atonia circuit

Brain systems and sleep

  • Basal forebrain
    • Induces slow-wave sleep via GABA release?
  • Hypothalamus
    • Coordinates between other areas
    • Orexin/hypocretin
  • Thalamus
    • Reticular nucleus

Thalamocortical circuits

Other structures and their functions

  • Pons
    • Triggers REM sleep
    • NE projection from Locus Coeruleus
    • Induces muscle atonia via strong GABA, glycine activation

Inducing sleep

Sleep and development

  • Sleeping like a baby
    • Babies sleep 70% of the time
    • Mostly in REM
    • But, no stable pattern before 3.5-4 mos
  • Sleep disorders common in elderly

Sleep and development

Sleeping around the animal kingdom

  • Highly variable patterns
  • Mammals and birds show SWS & REM

Why do we sleep?

  • Animals with higher metabolic rate -> more sleep
  • Avoid predators
  • Conserve energy
  • Restore body
    • Growth hormones released, but
    • Amount of exercise unrelated to sleep duration
  • Consolidate learning & memory

Sleep, Learning & Memory

Main points

  • Sleep – Get some!
  • Your brain needs it

References

Diekelmann, Susanne, and Jan Born. 2010. “The Memory Function of Sleep.” Nature Reviews Neuroscience 11 (2). Nature Publishing Group: 114–26. doi:10.1038/nrn2762.

Hobson, J Allan, and Edward F Pace-Schott. 2002. “The Cognitive Neuroscience of Sleep: Neuronal Systems, Consciousness and Learning.” Nature Reviews Neuroscience 3 (9). Nature Publishing Group: 679–93. doi:10.1038/nrn915.

Klemm, WR. 2011. “Why Does Rem Sleep Occur? A Wake-up Hypothesis.” Frontiers in Systems Neuroscience 5. Frontiers Media SA. doi:10.3389/fnsys.2011.00073.

McGregor, Ronald, and Jerome M Siegel. 2010. “Illuminating the Locus Coeruleus: Control of Posture and Arousal.” Nature Neuroscience 13 (12). Nature Publishing Group: 1448–9. doi:10.1038/nn1210-1448.

Peplow, Mark. 2013. “Structure: The Anatomy of Sleep.” Nature 497 (7450). Nature Publishing Group: S2–S3. doi:10.1038/497S2a.