Ch. 8 - Wakefulness & Sleep

endogenous circannual rhythm

selfgenerated rhythm that lasts about a year

endogenous circadian rhythms

internal biological process that repeats on an approximately 24-hour cycle

zeitgeber

stimulus that resets the circadian rhythm

jet lag

a disruption of circadian rhythms due to crossing time zones

pineal gland

an endocrine gland located just posterior to the thalamus that releases the hormone melatonin

melatonin

hormone that influences both circadian and circannual rhythms

superchiasmatic nucleus 

• the main driver of rhythms for sleep and body temperature

• part of the hypothalamus

• located above the optic chiasm

• generates circadian rhythm automatically

what produces melatonin

pineal gland

Hoagland’s Hypothesis

theory proposing that a biological clock mediates metabolic rate, and affects protensity

Protensity

subjective experience of time

biological clock

brain structure or mechanism mediating circadian rhythm and protensity

ventrolateral preoptic nucleus

cell group in anterior hypothalamus mediating sleep onset, if it’s stimulated, you sleep (Sleep ON switch)

• inhibits and is inhibited by “arousal system“

Arousal System

1. pons —→ ACh

2. Locus Coeruleus —→ NE (Neurepinephrine)

3. Raphe Nuckei —→ 5-HT

4. Tuberomammillary nucleus —→ histamine origin

Motivation to stay awake

orexin holds awake switch ON

• no orexin = narcolepsy (sleep attacks)

adenosine

accumulates in the basal forebrain during the day and activates VLPO circuit that inhibits arousal system

how does caffeine keep us awake?

it is an adenosine receptor bloacker, no Basal Forebrain activation of VLPO inhibition

median preoptic area

linked to neighboring VLPO, receives input from skin’s thermoreceptors

polygraph

instrument that simultaneously records changes in physiologicial processes — lie detector 

• also used to measure sleep

Polysomnograph (PSG)

multiple, coincident polygraph measures to provide a comprehensive assessment of sleep

Electroencephalogram (EEG)

record of voltage between 2 electrodes applied to scalp representing the activity of may neurons over time

• EEG ACTIVITY DEFINES SLEEP

Electromyogram (EMG)

record of gross motor unit potentials

what activity means what?

• Beta activity: Awake and alert

• beta transitions to alpha activity: awake and relaxed 

Stage 1 sleep

alpha transitions to theta activity

Stage 2 sleep

theta activity

• sleep spindles (low frequency bursts)

• K-complexes (high frequency bursts)

stage 3 & 4 sleep

theta activity transitions to delta activity

• <50% trace of delta = 3rd stage

• >50% trace of delta = 4th stage

REM sleep

theta activity and beta activity, called paradoxical sleep because brain is active 

• sleep rotates between REM and N-REM (stages 1-4) sleep in 90 min cycles

REM Rebound

increase in the proportion of time spent in REM sleep in an individual deprived of REM sleep

3 big theories of WHY we sleep

1. Evolutionary Theory: conserve energy and avoid danger

2. Restoration Theory: recover from daily exertions

• anabolic activity at night (rebuild, regrowth)

3. Ontogenetic Theory: facilitate neural organization

coma

extended period of unconsciousness caused by head trauma, stroke, or disease.

unresponsive wakefulness syndrome

alternates between sleep and moderate arousal, but even during the more aroused state, the peson shows no awareness of surroundings and no purposeful behavior

minimally conscious state

condition of decreased brain activity with occasional, brief periods of purposeful actions and limited speech comprehension

brain death

condition with no sign of brain activity and no response to any stimulus

slow-wave sleep

heart rate, breathing rate, and brain activity decrease, while slow, large-amplitude waves increase

reticular formation

a structure that extends from the medulla into the forebrain; controls motor areas of the spinal cord and selectively increases arousal and attention in various forebrain areas

pontomesencephalon

part of the reticular formation that contributes to cortical arousal

locus coeruleus

a small structure in the pons that emits bursts of impulses in response to meaningful events, especially those that produce emotional arousal

somnambulism

sleep walking

insomnia

inadequate sleep

sleep apnea

impaired ability to breathe while sleeping

periodic limb movement disorder

sleep disorder characterized by repeated involuntary movement of the legs and sometimes the arms

REM behavior disorder

people move around vigorously during REM sleep

night terror

experience of intense anxiety from which a person awakens screaming in terror

activation-synthesis hypothesis

idea that a dream represents the brain’s effort to make sense of sparse and distorted information

neurocognitive model

view that regards dreaming as thinking that occurs under conditions of decreased arousal and decreased sensory input