15/24: Sleep

electrophysiological measurements of sleep

• Electroencephalogram (EEG) → electrodes placed on scalp, measures brain activity

• Electromyogram (EMG) → electrodes placed on chin, measures muscle activity

• Electro-oculogram (EOG) → electrodes placed near eyes, measures eye movements

sleep cycle

→ depicted by EEG signals of sleep-related neural activity, in 4 stages:

1. Beta waves → 13-30 Hz

   • Prominently occurs during aroused states

   • Desynchronous activity → high frequency, low amplitude oscillations (periods)

2. Alpha waves → 8-13 Hz

   • Prominently occurs during relaxed state

3. Theta waves → 4-8 Hz

   • Prominently occurs during earlier stages of sleep

   • Intermittently occurs in drowsy states

4. Delta waves → = <4 Hz

   • Prominently occurs during deepest stages of sleep

   • Synchronous activity → low frequency, high amplitude oscillations (periods)

rapid eye movement sleep

REM sleep, paradoxical sleep → place to escape reality

Characteristics:

• Rapid eye movements

• Dreaming

• Desynchronized EEG activity (similar to beta waves)

• Muscle paralysis (besides from some sleep twitches)

• ↑ Cerebral blood blow

• ↑ Oxygen consumption

slow-wave sleep

deep sleep → stage 3/4, non-rem sleep, corresponding to neural waves with low frequency and low amplitude oscillations

• Reflects synchronized burst patterns of APs in brain nuclei

sleep deprivation studies

WHY IS IT ALWAYS RODENTS T _ T

• Originally Revealed muscular atonia effect of REM

Sleep loss leads to: Death. Or any other negative symptom you can imagine, sooner or later. Too lazy to write them all cmon now…

Takeaway: Don’t enable chronic sleep loss. Avoid microsleeps, sleep disruptions, or sleep “debts” to maintain proper health — prioritize sleep hygiene.

animal sleep

→ varies from humans, but seemingly a universal process (i.e., all animals may sleep)

Variations:

• Duration (amount of sleep)

  • Length of sleep cycles

• Ratio of REM:NREM

• Status of predation

  • Predators → indulge in longer, uninterrupted sleep

  • Prey → sleep more often, but for shorter

• Body weight requirements

Notable variation examples:

• Humans

  • Adults → ~7-hour periods (25% REM, 75% NREM)

  • Newborns → ~16-hour periods (50% REM, 50% NREM)

• Dolphins → “sleep” between 2 cerebral hemispheres (i.e., one can be awake while the other rests)

sleep metabolism

→ considered relationships revealed from animal sleep studies

Characteristics of larger, more complex animals:

• ↑ Basal (overall) metabolic rate = ↑ Body mass

  BUT

• ↑ Body mass = ↓ Metabolic rate per kg (cellular units)

  THEREFORE

• ↓ Metabolic rate per kg (cellular units) = ↓ Heart rate = ↑ Life span

  +

• ↑ Length of sleep cycles (restoration)

• Hypothesized to be related to economies of scale related to heat (energy) savings and nutrient-waste distribution networks

main theories for animal sleep

1. Recover from physical or mental exhaustion (energy maintenance)

   • Theoretically, this represents the tendency to have an equal ratio between energy-expensive activity and sleep recovery, but this isn’t particularly reliable;

   • (Lack of) empirical evidence:

     • Sudden changes in activity don’t correlate with amount of sleep

     • Caloric difference between sedentary state and sleeping for the same amount of time is negligible (~110 calories)

2. Brain processing (improve cognition - learning & memory)

   • Subconscious period give the brain the opportunity to reorganize data and archive memories, which isn’t always done efficiently while awake (synaptic modifications and inter-/intracellular processing does occur in sleep)

   • Empirical evidence: Amount of slow-wave + REM sleep correlates w/ improved cognition

3. Waste removal

   • Based on the understanding that amount of sleep often correlates with body size

   • Sleep gives the critical opportunity to do efficient metabolic processes

   • Empirical evidence:

     • [ Proteins ] in the brain ↓ from sleep but not wakefulness

     • Glial cells (astrocytes) seems to lose water weight and shrink, ↑ interstitial space/extracellular solution + ↑ CSF diffusion

       • Adaptation of bigger animals (who may benefit from economy of scale)

glymphatic system

→ refers to the process of cerebrospinal fluid (CSF) diffusing in the brain and becoming the extracellular solution that surrounds nervous cells (neurons) that ALSO clears neuronal waste products from the interstitial space

• Supposedly pops off during sleep : D

• Specialized from the lymphatic system, which clears away cellular waste from all other somatic cells

circadian rhythms

→ behavioural and physiological changes that function on a 24-hour cycle; sleep-wake cycle

• Controlled by internal biological clocks that are normally adjusted to daily variation in light levels (but still able to function in the absence of these light levels)

• However, continuous lack of variation in light levels can significantly skew the cycle

suprachiasmatic nucleus

SCN → body’s master clock; part of the hypothalamus that regulates circadian rhythms

• Lesioning results in dramatic alterations to circadian rhythms

  • ex. Sleep-wake hormonal secretions

  • ex. Sleep cycles

biological clocks

→ refers to the 2 interlocked negative feedback loops operating SCN neurons:

• Advanced sleep phase syndrome → mutation of the per2 gene, causing a 4-hour advance

• Delayed sleep phase syndrome → mutation of the per3 gene, causing a 4-hour delay

sleep-promoting molecule hypothesis

→ consistent with the waste removal theory of sleep — molecules promote drowsiness and sleep at ↑ [ ]

• [ Adenosine molecules (part of ATP) ] ↑ during waking hours + accumulate w/ sleep deprivation

• Drowsiness and sleep quality (duration & depth) are strongly modulated by adenosine receptor signaling

• Finding: Adenosine is 1 of many sleep-promoting molecules (whose cumulative effect of occurs after some duration of wakefulness)

  • Caffeine is an agonist that combats this effect

wake-promoting molecules

→ display ↑ activity during periods of arousal, alertness, and wakefullness (therefore ↓ activity during sleep)

• Acetylcholine

Hindbrain:

• Serotonin (from raphe nuclei)

• Norepinephrine (from locus coeruleus)

Hypothalamic:

• Orexin

• Histamine

ventral lateral preoptic area

vlPOA → associated neurons inhibit wake-promoting neurons, promoting sleep

• Sleep-wake flip-flop circuit → characterized by reciprocal inhibition (area receiving inhibitory input comes from the same region it’s inhibiting), such that both regions cannot be active at the same time + the transition is fast

  • In English: There’s biological/physiological grounding for the reason you can’t be awake and asleep at the same time + why you properly wake up or fall asleep almost instantly

Direct interventions:

• Electrical stimulation can facilitate drowsiness and perhaps sleep

• Lesions suppress sleep and cause insomnia

orexin

hypocretin → peptide produced by neurons in the lateral hypothalamus (LH) which promotes wakefulness

• Conscious motivation to remain awake will activate associated neurons;

• Most forms of narcolepsy associated to a lackthereof

  • Autoimmune destruction usually occurs in adolescence or young adulthood

narcolepsy

→ rare sleep disorder characterized by periods of excessive daytime sleepiness and/or irresistible urges to sleep

Significant symptoms:

• Sleep paralysis → paralysis associated to REM (or the lighter stages of sleep)

  • Often accompanied by vivid, dream-like hallucinations

• Cataplexy → complete muscle paralysis occurring in wake

  • Often precipitated by strong emotional reactions or sudden physical effort

insomnia

→ characterized by difficulty falling asleep after going to bed and/or after awakening during the night — being ass at sleeping

• Affects 25% of population occasionally, 9% chronically

Extreme versions (leading to death):

• Fatal familial → involves progressive worsening leading to hallucinations, delirium, confusion, etc.

• Sporadic fatal → associated with progressive neurodegeneration around the thalamus, hypothalamus, and/or brainstem

non-REM parasomnias

→ characterized by the brain’s confusion with transitioning between sleeping and waking states

• Sleep- “activities” (-walking, -talking, -groaning, -crying, -eating, -masturbating, -teeth grinding, etc.)

  • Tend to be prevalent in youth

  • Episodes can last seconds or much longer

  • State of activity can be induced (due to biological or pharmacological means)

• REM-sleep behaviour disorder → neurological disorder in which the person does not become paralyzed during REM sleep, thus, they can act out their dreams

  • Appears to have some issue w/ neurodegeneration disorders or some genetic component

• Sleep terrors → characterized by overwhelming feelings of terror upon waking

  • Panic, screaming, bodily harm, and/or rash actions are common symptoms

  • Patients usually have little-to-no recollection of the experience after it passes (they usually find out from someone else)

  • Prevalent in PTSD patients