Unveiling Brain Rhythms: EEG Insights Into Sleep and Consciousness

1. Neuroscience: Exploring the Brain, 3e Chapter 19: Brain Rhythms and Sleep

2. Introduction • Rhythmic Activities • Sleeping and waking, hibernation, breathing, walking… • Cerebral cortex: Range of electrical rhythms depending on state of consciousness • EEG: Classical method of recording brain rhythms from cerebral cortex • Circadian rhythms: Change in physiological functions according to brain clock

3. The Electroencephalogram • The Electroencephalogram (EEG) • Measurement of generalized cortical activity • Noninvasive, painless • Diagnose neurological conditions such as epilepsy, sleep disorders, research

4. The Electroencephalogram • Recording Brain Waves • Electrodes to scalp, low-resistance connection • Connected to banks of amplifiers and recording devices • Voltage fluctuations measured (tens of microvolts) • Electrode pairs: Measure different brain regions • Set of simultaneous squiggles, voltage changes between electrode pairs

5. The Electroencephalogram • EEG records very small electrical fields generated by synaptic currents in pyramidal cells

6. The Electroencephalogram • Generating Large EEG Signals by Synchronous Activity

7. The Electroencephalogram • Magnetoencephalography (MEG) • Recording miniscule magnetic signals generated by neural activity • Comparison with EEG, fMRI, PET • MEG localizes sources of neural activity better than EEG • MEG cannot provide detailed images of fMRI • EEG, MEG measure neuron activity, • fMRI, PET changes in blood flow, metabolism

8. The Electroencephalogram • EEG Rhythms • Categorization of rhythms based on frequency • Beta: Greater than 14 Hz, activated cortex • Alpha: 8-13 Hz, quiet, waking state • Theta: 4-7 Hz, some sleep states • Delta: Less than 4 Hz, deep sleep • Deep Sleep • High synchrony, high EEG amplitude

9. The Electroencephalogram • A Normal EEG

10. The Electroencephalogram • Seizures and Epilepsy • Epilepsy: Repeated seizures • Causes: Tumor, trauma, infection, vascular disease, many cases unknown • Generalized: Entire cerebral cortex, complete behavior disruption, consciousness loss • Partial: Circumscribed cortex area, abnormal sensation or aura • ‘Absence’ (childhood)epilepsy : Less than 30 sec of generalized, 3 Hz EEG waves- no seizures

11. The Electroencephalogram • Generalized Epileptic Seizure

12. Sleep • Sleep • Universal among higher vertebrates • Sleep deprivation, devastating • One-third of lives in sleep state • Defined: “Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment.”

13. Sleep • Three Functional Brain States

14. Sleep • Physiological changes during non-REM and REM sleep Non-REM: Slow-wave (EEG< 4Hz (Δ)) sleep REM: Fast-wave (EEG > 14Hz (β)) sleep EEG pattern similar to awake states (α, β) Start of REM cycle: activity of cholinergic neurons REM cycle end: Activity of 5HT and NE neurons

15. Sleep • EEG Rhythms During Sleep

16. Sleep • Why Do We Sleep? • Recovery time for brain? • Restoration? • Sleep to rest and recover, and prepare to be awake again • Adaptation? • Sleep to keep out of trouble, hide from predators

17. Sleep • Functions of Dreaming and REM Sleep • Body requires REM sleep • Sigmund Freud: Dream functions- Wish-fulfillment, conquer anxieties • Allan Hobson and Robert McCarley: Activation-synthesis hypothesis • Avi Karni: Certain memories require strengthening period REM sleep

18. Sleep • Neural Mechanisms of Sleep • Critical neurons Diffuse modulatory neurotransmitter systems • Noradrenergic and serotonergic neurons: Fire during and enhance waking state; active at end of REM cycle • Cholinergic neurons: enhance REM events; active during waking; may initiate REM cycles • 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., inhibit motor neurons)

19. Sleep • Wakefulness and the Ascending Reticular Activating System • Giuseppe Moruzzi: • Lesions in midline structure (reticular ‘activating’ system) of brainstem: State similar to non-REM sleep • Lesions in lateral tegmentum: Does not cause non-REM state sleep • Electrical stimulation of midline tegmentum of midbrain: Cortex moved from slow, rhythmic EEGs of non-REM sleep to alert and aroused state

20. Sleep • 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)

21. Sleep • PET Images of Waking and Sleeping Brain • Control of REM Sleep by Brain Stem Neurons

22. Sleep • Sleep-Promoting Factors • Muramyl dipeptide: isolated from the CSF of sleep-deprived goats, facilitates non-REM sleep • Interleukin-1: Synthesized in brain (glia, macrophages), stimulates immune system • Adenosine: Sleep promoting factor; released by neurons; may have inhibitory effects of diffuse modulatory systems • Melatonin: Produced by pineal gland, released at night-inhibited during the day (circadian regulation); initiates and maintain sleep; treat symptoms of jet lag and insomnia

23. Sleep • Gene Expression During Sleeping and Waking • Cirelli and Tononi: Comparison of gene expression in brains of awake and sleeping rats • 0.5% of genes showed differences of expression levels in two states • Increased in awake rats • Intermediate early genes • Mitochondrial genes • Increased in sleeping rats: protein synthesis- and plasticity-related genes • Changes specific to brain not other tissues

24. Circadian Rhythms • Circadian rhythms • circa = approximately; dies = a day • Daily cycles of light and dark • Schedules of circadian rhythms vary among species • Physiological and biochemical processes in body: Rise and fall with daily rhythms • Daylight and darkness cycles removed, circadian rhythms continue • Brain clocks

25. Circadian Rhythms • Circadian rhythms and physiological functions

26. Circadian Rhythms • Biological Clocks (cont’d) • Free-run: Mammals completely deprived of zeitgebers, settle into rhythm of activity and rest, but drifts out of phase with 12 hr day/light cycle • Components of biological clock Light-sensitive input pathway  Clock  Output pathway

27. Circadian Rhythms • Circadian rhythms of sleep and wakefulness

28. Circadian Rhythms • The Suprachiasmatic Nucleus: A Brain Clock • Intact SCN produces rhythmic message: SCN cell firing rate varies with circadian rhythm • Each SCN cell is a small clock • TTX does not disrupt their rhythmicity • Suggests that action potentials don’t play a role

29. Circadian Rhythms • A New Type of Photoreceptor • Berson and colleagues: Discovered specialized type of ganglion cell in retina • Photoreceptor, but not rod or cone cell • Contains melanopsin, slowly excited by light • Synapses directly onto SCN neurons • SCN output axons: Parts of the hypothalamus, midbrain, diencephalons, use GABA as primary neurotransmitter, lesions disrupt circadian rhythms

30. Circadian Rhythms • SCN Mechanisms (Cont’d) • Molecular Clocks similar in humans, mice, flies, mold • Clock genes: Period (Per), Timeless (Tim), Clock • Takahashi: Regulation of transcription and translation, negative feedback loop

31. Concluding Remarks • Rhythms • Ubiquitous in the mammalian CNS • Intrinsic brain mechanisms • Environmental factors • Interaction of neural processes and zeitgebers (like SCN clock) • Function of rhythms • Unknown but arise mainly as a secondary consequence - Sleep research • Little known about why we sleep and the function of dreams and sleep

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

34. The Electroencephalogram • Mechanisms and Meanings of Brain Rhythms • Synchronized oscillation mechanisms • Central clock/Pacemaker • Collective methods (“jam session”) • Thalamus massive cortical input influence cortex • Neuronal oscillations • Voltage-gated ion channels

35. The Electroencephalogram • Functions of Brain Rhythms • Hypotheses • Brain’s way of disconnecting cortex from sensory input • No direct function, by-products of strongly interconnected circuits • Walter Freeman • Neural rhythms coordinate activity, synchronize oscillations, bind together

36. Circadian Rhythms • Biological Clocks • Jacques d'Ortous de Mairan • Mimosa plant • Leaf movement continues on ‘schedule’ in the dark sensing sun movement • Augustin de Candolle • Plant responded to internal biological clock • Zeitgebers (German for “time-givers”) • Environmental time cues • For mammals: Primarily light-dark cycle