Chapter 19 Outline

Brain Rhythms and Sleep

• EEG Signals

  • Electroencephalogram: a measurement of electrical activity from the surface of the scalp that shows generalized activity of the cerebral cortex

  • How it Works: EEG is noninvasive and painless, using electrodes to measure the voltage (low spatial resolution)

    • Electrodes: wires from pairs of electrodes → amplifiers and each recording measures voltage differences between two points on the scalp

    • Typical Reading: a set of many simultaneous squiggles, indicating voltage changes between pairs of electrodes

    • Amplitude: dependent on the number of active neurons and the synchronicity of the neurons firing

    • Tracking: electrical potentials from the soma and dendrites of pyramidal cells

    • Measurement: Hertz = cycles/sec

  • EEG During Alertness and Waking: high-frequency, low-amplitude

  • EEG During Nondreaming Sleep States, Certain Drugged States, and Coma: low-frequency, high-amplitude

• MEG

  • Magnetoencephalography: measures neuron currents that produce a magnetic field

    • Advantages: better at localizing the sources of neural activity in the brain (higher spatial resolution), particularly those deep below the surface

    • Uses: experimental studies of the human brain and its cognitive functions as well as an aid in the diagnosis of epilepsy and language disorders

• EEG Rhythms

  • Correlation: often correlate with particular states of consciousness

  • Main EEG Rhythms:

    • Gamma: activated cortex

    • Beta: activated or attentive cortex

    • Alpha: quiet, waking state

    • Theta: some sleep and waking states

    • Delta: deep sleep

    • Spindles: sleep

• Fourier Transformation

  • Definition: wave forms are combinations of sine waves

    • Sub-Frequencies: breaking EEG rhythms into its parts

• EEG Rhythms Among Species

  • Mice and Humans: similar alpha, spindles, and ripples rhythms

• Epilepsy

  • Characteristics: repeated seizures

    • Causes: tumor, trauma, genetics, infection, vascular disease, and many cases are unknown

  • Seizure: an extreme form of synchronous firing of brain regions that is not normally present

    • Results: very large EEG patterns and small motor patterns

    • Generalized Seizure: entire cerebral cortex, complete behavior disruption, loss of consciousness

    • Partial Seizure: circumscribed cortex area, abnormal sensation, aura (abnormal vision), or movement

    • Absence Seizure: less than 30 seconds of generalized 3 Hz EEG waves; body becomes still & the person is unresponsive

• Hypotheses for the Functions of Brain Rhythms

  • Hypothesis #1: Neural rhythms could coordinate activity of regions of the nervous system

  • Hypothesis #2: by synchronizing oscillation from different regions, brain bind together a single perceptual construction

  • Hypothesis #3: Some rhythms may no direct function—by-products of strongly interconnected circuits

• How are Brain Rhythms Set?

  • Pacemaker: A central clock/conductor that other neurons synchronize with

  • Collective Behavior: sharing or distributing the timing function among themselves by mutually exciting or inhibiting one another

• Polysomnogram

  • Polysomnogram: a test of sleep cycles and stages through the use of continuous recordings of different measures

    • Measures: EEG activity, EMG (muscle) activity, EOG (eye movement), ECG (heart rate), respiration rate, and other biological measures

• EEG Stages of Sleep

  • Awake: alpha, beta, and gamma rhythms

  • REM Sleep: beta and gamma rhythms (similar to wake state)

  • Stage 1 Non-REM Sleep: theta rhythms

  • Stage 2 Non-REM Sleep: spindle and K complex rhythms

  • Stage 3 Non-REM Sleep: delta rhythms (deep sleep)

• Ultradian Rhythms

  • Ultradian Rhythms: the 90 minute cycles of non-REM and REM sleep throughout the night

    • Balance of REM and non-REM: during the night, the duration of non-REM sleep reduces, and REM periods increase

• Phases of Sleep

  • Rapid Eye Movement (REM) Sleep: characterized by high-frequency, low amplitude EEG rhythms (paradoxical sleep)

    • Body: the body is experiences muscle atonia, except the eyes and respiratory muscles

    • Dreams: vivid and detailed illusions are characteristic of REM sleep

    • EOG: records rapid eye movement

    • ECG: records increased heart rate

    • Respiration Rate: increases during REM

    • Penile Erection: increases during REM

  • Non-REM Sleep: characterized by low-frequency, high-amplitude EEG rhythms

    • Body: slight, uncontrolled movements

    • Dreams: no complex dreams

    • EOG: records no eye movement

    • ECG: records decreased heart rate

    • Respiration Rate: decreases during non-REM sleep

    • Penile Erection: decreases during non-REM sleep

• Theories of Why We Sleep

  • Restoration: we sleep to rest and recover and to prepare to be awake again

    • Sleep Deprivation Consequences: can lead to serious physical and behavioral problems

    • Mice and Sleep Deprivation: an experiment to test the effects of sleep deprivation

      • Experimental Design: a yoked experiment, where two mice walked on a rotating platform, but only one was dunked in water if it started to fall asleep

    • Glymphatic System and Sleep Deprivation: the release of buildup from the brain → lymph nodes via CSF is disrupted without sleep

    • Cerebral “Rest”: it is possible that brain regions in the cerebral cortex can achieve some form of essential “rest: only during non-REM sleep

  • Adaptation: we sleep to keep us out of trouble, to hide from predators when we are most vulnerable or from other harmful features of the environment, or to conserve energy

  • Memory Consolidation: we sleep to consolidate our memories from the day

    • Mouse Experiment Results: place cells in rodents fired in response to stimuli throughout a maze in similar patterns while the rodent slept

    • Human Experiment Results: individuals that learned a task, slept normally, and redid the task were better than REM sleep-deprived individuals

• Sleep Disorders

  • Common Sleep Disorders: insomnia and sleep apnea

  • REM Behavior Disorder: lack of atonia during REM sleep, common in older men

  • Cataplexy: sudden atonia during wake

  • Sleep Paralysis: atonia during non-REM sleep

• Neural Mechanisms of Sleep

  • Diffuse Modulatory NT Systems: neurons most critical to the control of sleeping an waking are a part of this system

  • NE/5-HT: fire during waking and enhance wakefulness (locus coeruleus/raphe nuclei) (REM-off cells)

  • ACh: brainstem and basal forebrain neurons enhance critical REM events (REM-on cells)

  • Histamine: midbrain neurons fire to enhance wakefulness

    • Anti-histamine: (Benadryl) decreases wakefulness

  • Orexin (hypocretin): promotes wakefulness, inhibits REM sleep, enhances motor behavior, and regulates neuroendocrine system and ANS

    • Narcolepsy: loss of hypocretin neurons in the lateral hypothalamus

      • Effects: excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic hallucinations

• Neuronal Mechanisms of Sleep/Wake

  • Mutual Inhibition: sleep-promoting region in VLPA → ← brain stem and forebrain arousal systems (ACh, NE, 5-HT, and histamine)

  • Activation: hypocretinergic neurons in the lateral hypothalamus assists the arousal system

    • Result: motivation to remain awake

• Sleep-Promoting Factors

  • Adenosine: have an inhibitory effect on the diffuse modulatory systems that promote wakefulness

  • Nitric Oxide: triggers the release of adenosine

  • Interleukin-1: a cytokine (immune signaling chemical), synthesized in the brain, that promotes non-REM sleep and stimulates the immune system (inducing fatigue and sleepiness)

  • Melatonin: released at night and helps initiate and maintain sleep; sends info to the SCN

• Circadian Rhythms

  • Circadian Rhythms: the daily cycles of daylight and darkness that result from the spin of the Earth

  • Zeitgebers: environmental time cues (light/dark, temp, humidity variations); keeps organisms in phase

    • Free Run: in the absence of zeitgebers, mammals rhythms occur around 24 hours

      • Experiment: causing free-running causes a shift in the beginning and end of the rhythms but no significant changes in the length

  • Suprachiasmatic Nucleus: pair of neuron clusters in the hypothalamus (bordering the third ventricle) that serve as a biological clock

    • Communication: communicate through APs of efferent axons and rates of cell firing

      • APs: not necessary for SCN neurons to maintain their rhythm

    • Circadian Influence: ANS, body temp., adrenal gland hormones (cortisol), and neural circuits that control feeding, movement, and metabolism

    • Clock Genes: a molecular clock system that uses negative feedback (more protein builds up during the day, inhibits promoter factors, inhibits protein synthesis)

    • Retina: ganglion cells → SCN neurons (via the retinohypothalamic tract)

      • Type of Light Info: SCN neurons respond to the luminance of light stimuli rather than their orientation or motion

        • System: light-sensitive ganglion cells, with melanopsin, are slowly excited by light → SCN, which can reset the circadian clock there