Chapter 19: Brain Rhythms and Sleep

1. Neuroscience: Exploring the Brain, 4e Chapter 19: Brain Rhythms and Sleep …

2. Introduction • Rhythmic activities of the brain • Sleeping and waking, hibernation, breathing, walking, electrical rhythms of cerebral cortex • Cerebral cortex: range of electrical rhythms correlated with interesting behaviors • EEG: classical method of recording brain rhythms, essential for studying sleep • Circadian rhythms: changes in physiological functions according to brain clock

3. The Electroencephalogram (EEG) • Measurement of generalized activity of cerebral cortex • Helps diagnose neurological conditions, such as epilepsy and sleep disorders, and for research

4. Recording Brain Waves • Noninvasive, painless • Electrodes on scalp with low-resistance connection • Connected to banks of amplifiers and recording devices • Voltage fluctuations measured (tens of microvolts) • Electrode pairs: measure different brain regions • Amplitude of the EEG signal a measure of synchronous activity of underlying neurons

5. Generation of Electrical Fields Recorded by EEG

6. Generating Large EEG Signals by Synchronous Activity

7. Magnetoencephalography (MEG) • Recording of miniscule magnetic signals generated by neural activity • Compared with EEG, fMRI, PET • MEG localizes sources of neural activity better than EEG. • MEG cannot provide detailed images of fMRI. • EEG and MEG measure neuron activity. • fMRI and PET measure changes in blood flow or metabolism. • MEG and EEG can record rapid fluctuations of neuronal activity

8. Magnetoencephalography (MEG)—(cont.)

9. EEG Rhythms • Often correlate with particular states of behavior • Categorization of rhythms based on frequency • Beta: 15–30 Hz, activated or attentive cortex • Alpha: 8–13 Hz, quiet, waking state • Theta: 4–7 Hz, some sleep and waking states • Delta: less than 4 Hz, deep sleep • Spindles (8-14 Hz; sleep), ripples (8-200 Hz) • Deep sleep: high synchrony, high EEG amplitude

10. A Normal EEG

11. EEG Rhythms Across Species

12. Mechanisms of Synchronous Rhythms • Rhythms can be led by a pacemaker or arise from collective behavior of all participants.

13. A two-neuron oscillator.

14. A one-neuron oscillator.

15. Mechanisms of Brain Rhythms • Synchronized oscillation mechanisms • Central clock/pacemaker and/or collective methods • Thalamus  massive cortical input as pacemaker • Neuronal oscillations • Voltage-gated ion channels

16. Functions of Brain Rhythms • Hypotheses • Sleep as brain’s way of disconnecting cortex from sensory input • Some rhythms may have no direct function—by-products of strongly interconnected circuits • Walter Freeman: Neural rhythms coordinate activity of regions of the nervous system (burst of synchrony giving rise to EEG gamma rhythms). • By synchronizing oscillations from different regions, brain may bind together a single perceptual construction. Light-based therapy for Alzheimer's disease

17. Seizures and Epilepsy • Epilepsy causes repeated seizures. • Causes: tumor, trauma, genetics, infection, vascular disease, many cases unknown • Generalized seizure: entire cerebral cortex, complete behavior disruption, consciousness loss • Partial seizure: circumscribed cortex area, abnormal sensation or aura • Absence seizure: less than 30 seconds of generalized 3 Hz EEG waves • Causes (mutations in sodium channels, GABA receptors)

18. Incidence of epilepsy by age

19. An EEG of a Generalized Epileptic Seizure

20. Sleep • A readily reversible state of reduced responsiveness to, and interaction with, the environment • Universal among higher vertebrates • Sleep deprivation is devastating to proper functioning. • One-third of our lives spent in sleep state • Purpose of sleep still unclear

21. Three Functional Brain States

22. Physiological Changes During Non-REM and REM Sleep

23. EEG Rhythms during Sleep Stages

25. Why Do We Sleep? • All mammals, birds, and reptiles appear to sleep— apparently needed by the brain • Two main categories of theories of sleep function • Restoration • Sleep to rest and recover, and prepare to be awake again • Adaptation • Sleep to keep out of trouble, hide from predators • Conserve energy One more reason to get a good night’s sleep | Jeff Iliff Box 19.3 The longest all-nighter Why do we sleep? | Russell Foster

26. Functions of Dreaming and REM Sleep • Unclear why we dream—but body requires REM sleep • Sigmund Freud: dream functions—wish fulfillment, conquer anxieties • Hobson and McCarley: activation–synthesis hypothesis • Karni: Certain memories require strengthening time period  REM sleep. Why do we dream? - Amy Adkins

27. Neural Mechanisms of Sleep • Critical neurons  diffuse modulatory neurotransmitter systems • Noradrenergic and serotoninergic neurons: fire during and enhance waking state • Cholinergic neurons: Some enhance REM events, others active during waking. • Diffuse modulatory system control rhythmic behaviors of thalamus  controls cortical EEG  sensory input flow to cortex blocked by slowed thalamic rhythms • Activity in descending branches of diffuse modulatory systems (e.g., inhibitory neurons)

28. Wakefulness and the Ascending Reticular Activating System • Brain stem lesions cause sleep, coma • Moruzzi’s research • Lesions in midline structure of brain stem cause state similar to non-REM sleep. • Lesions in lateral tegmentum do not cause non-REM state sleep. • Electrical stimulation of midline tegmentum of midbrain changes cortex from slow, rhythmic EEGs of non-REM sleep to alert and aroused state.

29. Key Components of the Waking/Sleeping Modulatory Systems

30. Narcolepsy

31. Falling Asleep and Non-REM State • Sleep: progression of changes ending in non-REM state • Non-REM sleep: decrease in firing rates of most brain stem modulatory neurons using NE, 5-HT, ACh • Stages of non-REM sleep • EEG sleep spindles • Spindles disappear • Replaced by slow, delta rhythms (less than 4 Hz)

32. PET Images of Waking and Sleeping Brain

33. Control of REM Sleep by Brain Stem Neurons

34. Sleep-Promoting Factors • Adenosine: released by neurons; may have inhibitory effects of diffuse modulatory systems; caffeine antagonizes adenosine Rc. • Nitric acid (NO): triggers release of adenosine • Muramyl dipeptide: isolated from the CSF of sleep-deprived goats, facilitates non-REM sleep • Interleukin-1: synthesized in brain, stimulates immune system, induces fatigue and sleepiness • Melatonin: released at night, inhibited during daylight; helps initiate and maintain sleep—used to treat symptoms of jet lag and insomnia

35. Gene Expression during Sleeping and Waking • Cirelli and Tononi compared gene expression in brains of awake and sleeping rats. • 0.5% of genes showed differences of expression levels when awake or asleep. • Genes that increased in awake rats: intermediate early genes and mitochondrial genes • Genes that increased in sleeping rats: genes that contribute to protein synthesis and plasticity mechanisms • These changes specific to the brain, not other tissues

36. Circadian Rhythms • Daily cycles of light and dark • Schedules of circadian rhythms vary among species. • Most physiological and biochemical processes in body rise and fall with daily rhythms. • If daylight and darkness cycles are removed, circadian rhythms continue. • Brain clocks require occasional resetting.

37. Circadian Rhythms of Physiological Functions

38. Evidence for Biological Clocks • Jacques d'Ortous de Mairan • Mimosa plant leaf movement continues circadian rhythm even in the dark. • Augustin de Candolle • A plant in the dark responds to internal biological clock. • Zeitgebers (German for “time givers”) • Environmental time cues • For mammals: primarily light–dark cycle

39. Biological Clocks • Free-run: Mammals completely deprived of zeitgebers settle into rhythm of activity and rest but drift out of phase with 12-hour day/light cycle. • Behavior and physiology do not always cycle together. • Components of biological clock Light sensor  Clock  Output pathway

40. Circadian Rhythms of Sleep and Wakefulness

41. The Suprachiasmatic Nucleus (SCN) • Intact SCN produces rhythmic message: SCN cell firing rate varies with circadian rhythm. • Retinal input necessary to entrain sleep cycles to night How to prove that SCN is a clock . Lesion . Tau-mutant mice

43. Retinal Ganglion Cells • Berson and colleagues discovered specialized type of ganglion cell in retina. • Photoreceptor but not a rod or cone • Expresses melanopsin, slowly excited by light • Synapses directly onto SCN neurons to reset circadian clock • SCN output axons to parts of the hypothalamus, midbrain, diencephalons; use GABA as primary neurotransmitter

44. SCN Mechanisms • Molecular clocks similar in humans, mice, flies, mold • Clock genes: period (per), cryptochrome, clock • Takahashi: regulation of transcription and translation, negative feedback loop

45. Concluding Remarks • Rhythms ubiquitous in the mammalian CNS • Some from intrinsic brain mechanisms • Some from environmental factors • Some from interaction of neural processes and zeitgebers (like SCN clock) • Function of many neural rhythms unknown—may arise as a secondary consequence of other functions • Sleep research: Still little is known about why we sleep and the function of dreams and sleep.