1. Chapter 19: Brain Rhythms and Sleep
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.

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, ripples
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. 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

14. 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.
By synchronizing oscillations from different regions, brain may bind together a single perceptual construction.

15. 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

16. An EEG of a Generalized Epileptic Seizure

17. 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

18. Three Functional Brain States

19. Physiological Changes During Non-REM and REM Sleep

20. EEG Rhythms during Sleep Stages

21. 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

22. 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.

23. 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)

24. 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.

25. Key Components of the Waking/Sleeping Modulatory Systems

26. 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)

27. PET Images of Waking and Sleeping Brain

28. Control of REM Sleep by Brain Stem Neurons

29. Sleep-Promoting Factors
Adenosine: released by neurons; may have inhibitory effects of diffuse modulatory systems
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

30. 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

31. 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.

32. Circadian Rhythms of Physiological Functions

33. 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

34. Light sensor  Clock  Output pathway
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

35. Circadian Rhythms of Sleep and Wakefulness

36. 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

37. 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

38. 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

39. 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.