Glossary
While I have tried to keep the language in this website as non-technical as possible, it is not possible to entirely avoid jargon and technical and scientific terms, particularly in more technical sections like How Sleep Works, for example. This section provides a quick and dirty reference for some of these terms, again without going into too much technical detail. Words in blue bold in the definitions have their own entry in this Glossary.
acetylcholine | an important neurotransmitter in the peripheral and central nervous system,
involved with the transmission of nerve impulses throughout the
body |
actigraph | a wrist-mounted unit which
measures gross motor activity and movement, and therefore gives a
rough and ready guide to sleep and wake time over an extended
period (the physical output of an actigraph is called an actigram) |
activation-synthesis model | a theory of dreams in which, as circuits in the brain
become activated during REM
sleep, so do areas of the limbic system involved in emotions,
sensations and memories, and dreams are the brain’s attempts to
synthesize and find meaning in these random signals |
active unlearning | the theory that dreams actively help us to forget
non-meaningful or unwanted information by eliminating certain
synaptic connections and neural pathways, rather than storing it in
long-term memory |
adenosine | an inhibitory neurotransmitter and neuromodulator (as well as a major
molecular component of ATP, which transports chemical energy within
cells), that plays an important role in promoting sleep and suppressing arousal |
adrenaline | another name for epinephrine |
advanced sleep phase syndrome
(ASPS) | a circadian rhythm sleep disorder where a
person’s natural rhythm leads to difficulty staying awake in the
evening, and concomitant difficulty staying asleep in the
morning |
agonist | a drug or other chemical that
combines with a cell receptor to produce a physiologic reaction
similar to that of a naturally occurring substance (the opposite of
an antagonist) |
alpha waves | brain waves with a frequency of 8-13 Hz
(typical of resting wakefulness light non-REM sleep) |
amygdala | a structure in the limbic system of the brain, involved with
memory and emotions (particularly unpleasant emotions like anger
and fear) |
anabolic | a constructive metabolic process during which new
molecules are constructed and built up, and more complex substances
are synthesized from simpler ones, requiring energy |
anesthesia | general or local insensibility to
pain and other sensation, either as a result of nerve damage or the
deliberate administration of drugs (spelled anaesthesia in
England) |
antagonist | a substance or drug that
counteracts, blocks or inhibits the effects of another substance
or drug (the opposite of agonist) |
apnea | a pause in breathing of at least
10 seconds during sleep, which occurs as a result of sleep apnea
(spelled apnoea in England) |
arousal | an abrupt change from sleep to wakefulness (in which case it is also
called awakening), or from a
deeper stage of non-REM sleep to a lighter stage, measurable by encephalography |
arousal threshold | the relative ease or difficulty
with which a sleeper can be awakened at a particular time (e.g. by
a noise, by shaking, etc) |
atonia | the muscle paralysis, or complete
absence of muscle tone and
skeletal muscle activity, that accompanies REM sleep, when motor neurons are not stimulated (also called muscle atonia, muscular atonia, motor atonia or atony) |
auditory sleep start | another name for exploding head syndrome |
automatic behaviour | a symptom of narcolepsy, in which sufferers may
continue to perform normal daily activities or tasks during daytime sleep episodes even though
technically asleep, with little or no subsequent recollection of
the events, or of having slept at all |
awakening | the transition from sleep into wakefulness (also called arousal) |
bed-wetting | uncontrolled urination during sleep, particularly among
young children (also known as enuresis) |
beta waves | brain waves with a frequency of 12-30 Hz
(within the normal range for the active awake state) |
biphasic sleep | sleep broken up into two main chunks, separated
by an hour or two of quiet restfulness and interludes of sex,
common in nomadic or hunter-gatherer societies even today (also
called two-phase sleep) |
brainstem | the part of the brain connecting
the spinal cord to the main forebrain, and responsible
for the control and regulation of many vital body functions such as
respiration, heart rate and blood pressure |
brain waves | electrical impulses or
fluctuations of voltage between parts of the cerebral cortex in the brain that are
detectable with an electroencephalograph |
bright light therapy | a treatment for circadian rhythm sleep disorders in which
bright full-spectrum light is administered at desired wake-up times
and darkness maintained at sleep times, in an attempt to reset the
patient’s circadian
clock |
caretaker insomnia | sleep disruption experienced by parents
of newborn babies, or adults who care for family members with
medical disorders, etc |
catabolic | a destructive metabolic process during which molecules
are broken down for subsequent re-use, and more complex substances
are disassembled simpler ones, releasing energy in the
process |
cataplexy | a symptom of narcolepsy, in which sudden muscular
weakness is experienced during periods of wakefulness, similar to the muscle atonia normally experienced during REM sleep (also called a cataplectic attack) |
catathrenia | a parasomnia in which the breath is held
during REM sleep, followed by
a long drawn-out groaning, wheezing or squeaking sound during
exhalation (also called nocturnal groaning) |
cathemeral | animal behaviour characterized by
sporadic, irregular and random internals of activity and sleep during the night or
day |
central nervous system | that part of the nervous system
responsible for the coordination of motor and mental activities,
consisting of the brain and the spinal cord (i.e. excluding the
peripheral nervous system) |
central sleep apnea | a relatively uncommon variant of sleep apnea which occurs when
the brain fails to send the signal to the muscles to take a breath
during sleep, and so there is
no muscular effort to take a breath |
cerebral cortex | the folded and furrowed sheet of
neural tissues, forming the outer surface of the brain, which is
associated with consciousness, awareness and higher functions such
as voluntary movement, coordination of sensory information,
attention, learning and memory and the expression of individuality
(sometimes just cortex) |
chronic insomnia | ongoing insomnia symptoms that recur at least two
days a week for at least a month (also called persistent
insomnia) |
chronobiology | the science of timing medical
attention to various organisms of the body depending on the most
propitious time of day for those particular organs, according to
their particular biological rhythms |
chronotherapy | a treatment for circadian rhythm sleep disorders in which
the patient’s circadian clock is gradually reset by the systematic manipulation of sleeping and
waking times |
chronotype | an assessment of what time of day
a particular person’s physical functions are most active, depending
on their particular circadian
rhythms, e.g. whether they are “larks” (morning
people), or “owls” (evening people) |
circadian alerting system | an alerting pulse sent out by the suprachiasmatic nucleus throughout the day, which counteracts the increasing homeostatic sleep pressure and creates
the circadian drive for
arousal |
circadian clock | the biochemical mechanism, located
in the suprachiasmatic
nucleus of the hypothalamus in the human brain, that
regulates the circadian
rhythm of an organism (also known as the biological
clock, body clock, circadian pacemaker, circadian system, circadian oscillator, etc) |
circadian drive for arousal | a tendency towards wakefulness, arousal and alertness, generated by the
alerting pulses of the circadian
alerting system |
circadian period | the length of the circadian rhythm of an individual, which
typically varies between 23.5 and 24.5 hours, with an average of
around 24.2 hours |
circadian rhythm | a daily cycle of biological
activity (including sleep-wake regulation and the circadian alerting system, hormone secretion, body temperature,
etc), based on a roughly 24-hour period, and regulated by the
body’s internal circadian
clock in conjunction with external stimuli such as the light-dark cycle (also called circadian cycle) |
circadian rhythm sleep disorders
(CRSD) | a family of related sleep disorders, all characterized by an
inability to sleep and/or
wake at appropriate times, due to the dictates of the individual’s circadian clock |
cognitive behavioural therapy
(CBT) | a psychotherapeutic approach to
dealing with sleep disorders by firstly convincing a patient that their problems are manageable,
and secondly establishing a good system of sleep hygiene |
coma | a state of prolonged
unconsciousness and unresponsiveness to external stimuli, from
which arousal is not possible |
conditioned insomnia | insomnia perpetuated by stress and
anxiety about difficulties sleeping |
confusional arousal | a parasomnia, similar to but less violent
than a night terror, in which
a period of movement and crying gives way to a partial and confused awakening, marked by
disorientation, mental dullness, slurred speech and slowed
reactions (also called sleep drunkenness) |
continual-activation theory | a theory of dreams which asserts that dreams are part of the brain’s
consolidation of working memories into long-term memories |
continuous positive airway pressure
(CPAP) | the most effective treatment for obstructive sleep apnea, in
which mild air pressure from a machine helps to keep an airway open
during sleep |
cortisol | a hormone, produced in the adrenal gland,
that helps regulate metabolism, blood sugar levels and the immune system (also called hydrocortisone, and sometimes called the stress
hormone as it is also released in response to stress) |
cortisol awakening response | an increase of up to 50% in levels
of the hormone cortisol, which occurs 20-30 minutes
after awakening in
preparation for the anticipated stress of daytime activities |
co-sleeping | a sleep practice where a baby or young
child sleeps in the same bed as its mother, common up until the
19th Century, and outside of the industrialized West even
today |
crepuscular | animal behaviour characterized by
activity mainly during the twilight hours of dawn and dusk |
cytokines | proteins (including interleukin and interferon) produced by the immune system while fighting an
infection, which also act as powerful sleep-inducing chemicals |
daydream | a level of consciousness somewhere
between sleep and wakefulness, in which the
mind begins to wander and the imagination may create imagined
scenarios and fantasies (usually pleasant and positive) |
delayed sleep phase syndrome
(DSPS) | the most common circadian rhythm sleep disorder where a
person naturally has a much later-than-normal timing of sleep onset, and may
experience peak alertness in the middle of the night |
delta waves | brain waves with a frequency of 0.5-4 Hz
(typical of deep slow-wave non-REM sleep) |
diurnal | animal behaviour characterized by
activity during the daytime and sleep at night |
dopamine | a neurotransmitter in the central nervous system that helps
regulate movement and emotion, and is also involved in dreams |
dream | images, ideas, emotions and
sensations that occur involuntarily in the mind during sleep, mainly during periods of REM sleep |
dyssomnia | another name for sleep disorder |
electroencephalography (EEG) | a technique for measuring the
electrical activity of the brain using electrodes on the scalp to
measure electrical potentials in the brain (an electroencephalograph is the machine that creates this
record, and an electroencephalogram is the physical output
of the process) |
electromyography (EMG) | a technique for measuring the
electrical activity of the skeletal muscles (an electromyograph is the machine that creates this record, and
an electromyogram is the physical output of the
process) |
electrooculography (EOG) | a technique for measuring the
electrical activity of the retina of the eye over a period of time
(an electrooculograph is the machine that creates this
record, and an electrooculogram is the physical output of
the process) |
encephalitis lethargica | a rare viral infection of the hypothalamus, resulting in
extreme lethargy, sleep
period inversion, even catatonia or an unresponsive
coma-like state |
endogenous | naturally produced by the body
itself, i.e. originating, growing or developing from within an
organism, rather than externally |
epinephrine | a hormone and neurotransmitter involved in the
regulation of heart rate, blood vessels, air passages, metabolic
shifts and the fight-or-flight response (also called adrenaline) |
episodic insomnia | insomnia symptoms that last up to three
weeks (also called short-term insomnia) |
Epworth sleepiness scale | a quick and cheap diagnostic tool
for sleep disorders,
consisting of just eight simple questions about daytime sleep propensity |
estivation | the habit of some mammals,
reptiles and amphibians of passing the hottest and/or driest months
of the year in a dormant condition with a greatly reduced metabolism (the hot weather
equivalent of hibernation)
(spelled aestivation in England) |
excessive daytime sleepiness
(EDS) | a major symptom of narcolepsy and hypersomnia and a secondary symptom of
many other sleep disorders,
characterized by a difficulty in maintaining wakefulness during the day, a tendency to
fall asleep when seated or resting, and a general listlessness and
lack of energy (also called somnolence) |
excite | to encourage or speed up a
chemical reaction or process (a substance, such as a neurotransmitter, that excites a process
is called excitatory) |
exploding head syndrome | a parasomnia in which a person experiences
a sudden load noise, sometimes accompanied by a flash of light and
a sense of fear or anxiety, apparently from within their own head,
just as they are about to fall asleep (also called an auditory
sleep start) |
extreme napping | a planned sleep pattern consisting of segmented and
broken-up sleep periods, e.g.
15-minute naps every 4 hours
throughout the day and night (also called polyphasic sleep or polycyclic sleep) |
fatal familial insomnia (FFI) | a very rare fatal sleep disorder in which malformed proteins called prions attack
the sufferer’s thalamus |
forebrain | the main part of the brain
(including the cerebral
cortex, limbic system, thalamus and hypothalamus, and excluding the brainstem) |
free-running sleep | sleep that is not adjusted or entrained
to the usual 24-hour cycle (e.g. in sleep experiments involving constant
light or constant darkness) |
gamma waves | brain waves with a frequency of 25-100 Hz
(within the normal range for the awake state) |
ganglion cells | photoreceptive neurons found near the inner surface of
the retina of the eye, which transmit visual information on the light-dark cycle to the
brain |
gene | a sequence of molecules in a
segment of DNA that provides coded instructions leading to the
expression of particular hereditary characteristics in the organism
(genetics is the science of heredity) |
glutamate | the most common excitatory neurotransmitter in the nervous system,
with a key role in learning and memory among other things |
glycogen | the main form of energy storage in
animals, stored in the liver and muscles, and easily convertible
into glucose |
growth hormone | a hormone, essential to the repair and
restoration processes of the body and mainly secreted during non-REM sleep, that
stimulates growth and cell reproduction and regeneration |
hallucination | waking dreams, often as a result of a mental or
physical disorder, in which vivid and substantial perceptions occur
in the absence of external stimuli, but which nevertheless have a
compelling sense of reality |
hibernation | the habit of some mammals,
reptiles and amphibians of passing the winter in a dormant
condition with a greatly reduced metabolism |
histamine | a neurotransmitter released by the body
during allergic reactions and immune responses, as well as in sleep modulation |
homeostasis | any internal biochemical system
that regulates the internal environment, with a view to maintaining
body properties such as temperature, acidity, etc , in a stable and
relatively constant condition (e.g sleep-wake homeostasis) |
homeostatic sleep drive | the pressure to sleep, generated by the process of sleep-wake homeostasis (also
called homeostatic sleep pressure) |
hormone | a chemical substance, secreted by
the endocrine glands and transported through body fluids such as
the blood, to affect the functions of specific organs or tissues in
different parts of the body |
hypersomnia | a sleep disorder characterized by excessive daytime sleepiness,
excessive sleep periods each
day or just an inability feel refreshed even after an apparently
adequate sleep period (also
called hypersomnolence or idiopathic
hypersomnia) |
hypnagogic | relating to the drowsy state just
before sleep onset |
hypnic jerk | a sudden twitch or start, often
accompanied by a falling sensation and a short awakening, commonly experienced just as a
person is starting to fall asleep (also known as a hypnagogic
jerk or sleep start) |
hypnogenic | sleep inducing (e.g. a substance in the
body, or a drug) |
hypnogram | a simplified graph representing
the stages of sleep (based on electroencephalography recordings over the period of a night) as a function of time |
hypnopedia | another name for sleep learning |
hypnophobia | an anxiety disorder manifesting as
an abnormal fear of sleeping or going to bed (also called somniphobia or negative sleep conditioning) |
hypnopompic | relating to the drowsy
semi-conscious state just before complete wakefulness |
hypnotic trance | a semi-conscious state induced by
hypnosis in which a person is apparently unaware of the environment
and is highly susceptible to suggestion |
hypocretin | another name for orexin |
hypothalamus | a region of the brain, located
between the thalamus and the
mid-brain, which acts as a major control centre for the autonomous
nervous system, regulating sleep
cycles, body temperature, appetite, hormone production, etc |
idiopathic | arising spontaneously, not
resulting from any other disease, arising from no known cause or
trigger |
idiopathic insomnia | persistent insomnia, usually beginning in childhood,
which is unrelated to psychosocial stressors or medical
disorders |
immune system | the network of cells, biological
structures and processes that work to protect an organism from
diseases and foreign substances |
inhibit | to stop, or decrease the rate of,
a chemical reaction or process (a substance, such as a neurotransmitter, that inhibits a process
is called inhibitory) |
insomnia | a general term for any difficulty
in falling asleep or staying asleep, such that the sufferer is
still tired, unrefreshed and unrested on waking |
irregular sleep-wake rhythm disorder
(ISWRD) | a circadian rhythm sleep disorder, mainly
found in sufferers from dementia, where a disrupted circadian rhythm leads to numerous naps at irregular times
throughout a 24-hour period, with no main nighttime sleep episode (polyphasic sleep) |
jet lag | a temporary mismatch between the
external environment and a person’s internal circadian clock that occurs when someone
travels rapidly across multiple time zones (e.g. in an airplane),
causing sleep patterns to be
impacted (sometimes recognized as a sleep disorder, even though it is usually
short term and self-imposed) |
K-complex | a short negative high voltage peak
in brain wave activity,
followed by a slower positive complex, and then a final negative
peak, with each complex lasting 1-2 minutes, typically experienced
during Stage 2 non-REM sleep |
Kleine-Levin syndrome | an extreme variant of hypersomnia occurring in teenage boys, in
which sufferers may sleep for
several days at a time, waking ravenously hungry, irritable and
sometimes hypersexual (also known as Sleeping Beauty
syndrome) |
light-dark cycle | the natural daily cycle between
sunlight and darkness resulting from the Earth’s turning on its
axis |
light sleep | the early stages of a sleep cycle, comprising stage 1 and stage 2 non-REM sleep, in which brain wave activity is still relatively
fast and awakening is
relatively easy |
limbic system | a group of structures deep in the
centre of the brain, including the hippocampus and amygdala, which are involved in emotion,
behaviour, motivation, memory, olfaction, and various autonomic
functions |
locus coeruleus | a group of neurons in the pons region of the brainstem responsible for the blocking or inhibition of motor signals
during the atonia of REM sleep (also spelled caeruleus or ceruleus) |
long-term memory excitation
theory | a theory of dreams which argues that dreams are just the brain’s internal
excitations of already existing long-term memories (a process which
is going on all the time, but the suppression of the “reality
checking” of the brain’s executive function during sleep allows us to notice it) |
lucid dreams | extremely realistic and vivid dreams, in which the sleeper
is actually aware of dreaming, and in which it may be possible to
consciously continue, or even to exert some control over, the dream |
maintenance of wakefulness test
(MWT) | a method of measuring daytime
sleepiness, by looking at an individual’s ability to stay awake
while reclining in a quiet darkened room |
melanopsin | a light-sensitive pigment (most
sensitive to short wavelength “blue light”) in the ganglion cells of the retina of the
eye |
melatonin | a naturally occurring hormone, secreted in the pineal gland in the brain in response to
darkness, that plays a key role in biological circadian rhythms such as sleep and reproductive cycles |
memory bias | a deviation in judgement or
perceptual distortion, either deliberate or subconscious, that
enhances, impairs or changes a particular memory, making it
unreliable |
memory consolidation | the stabilization and
strengthening of a memory trace after its initial acquisition,
through the repeated reactivation of synaptic connections and pathways within
a neural network |
metabolic process | an organic process in a cell or
organism that is necessary for life, collectively known as metabolism |
metabolism | the physical and chemical
processes (which may be anabolic or catabolic) by which an organism functions
and operates, and by which it grows, reproduces, maintains its
structures and responds to its environment |
metaturnal | animal behaviour characterized by
activity (and sleep) partly
during the day and partly at night |
micro-awakening | a very short awakening during a sleep period, of just a few seconds or
even fractions of a second, often not consciously recognized or
remembered |
microsleep | a very short episode of sleep during a period of wakefulness, lasting from a
fraction of a second up to about 30 seconds, often resulting from sleep deprivation or sleep disorders |
mixed sleep apnea | a relatively rare combination of central sleep apnea and obstructive sleep apnea |
monophasic sleep | sleep organized into just one long period
each day (also called monocyclic sleep) |
multiple sleep latency test
(MSLT) | a method of measuring daytime
sleepiness, by looking at the time needed to go from wakefulness to sleep onset in a series of daytime nap opportunities at two hour
intervals |
muscle atonia | another name for atonia (also called muscular
atonia, motor atonia or atony) |
muscle tone | the amount of tension, or
resistance to passive stretching, in the muscles, which helps to
maintain posture, and which is dramatically reduced during the atonia of REM sleep (also called tonus) |
nap | a brief period of sleep taken outside of the main sleep period, i.e. usually
during the daytime (also known as a siesta) |
narcolepsy | a chronic sleep disorder characterized by
uncontrollable excessive daytime
sleepiness, sleep attacks at inappropriate times, hallucinations, automatic behaviour, episodes of sleep paralysis and/or cataplexy, and an abnormal
tendency to pass directly into REM
sleep from wakefulness |
negative sleep conditioning | another name for hypnophobia |
nerve cell | another name for neuron |
neural network | a group or circuit of neurons connected or functionally related
to each other through synapses and synaptic connections |
neuromodulator | a neurotransmitter (such as dopamine, serotonin, histamine, acetylcholine, etc) which diffuses
through large areas of the nervous system, thereby affecting many
different neurons |
neuron | a specialized electrical
impulse-conducting cell that processes and transmits information
through the brain and nervous system by means of electrical and
chemical signals (also known as a nerve cell) |
neuronal group theory of sleep | the theory that individual groups
of neurons in the brain enter
into a state of sleep after a
certain threshold of activity has been reached, and that, once
enough groups of neurons are
in this sleep state, the
whole organism falls asleep |
neurotransmitter | a chemical substance that transmit
signals, or nerve impulses, between neurons across a synapse (examples include acetylcholine, adenosine, glutamate, epinephrine, norepinephrine, dopamine, serotonin, histamine, orexin, etc) |
nightmare | an unpleasant dream with particularly vivid and
disturbing content, usually accompanied by a strong negative
emotional response (e.g. fear, horror, despair, anxiety, sadness,
etc) and often resulting in awakening |
night terror | a parasomnia manifesting as intense,
violent and inconsolable feelings of terror or dread on waking from
deep slow-wave sleep, often
accompanied by screaming, thrashing, a period of confusion and
almost complete amnesia (also called sleep terror or pavor nocturnus) |
nocturia | an excessive need for nighttime
urination, particularly common in pregnant women and the elderly
(also called nycturia) |
nocturnal | animal behaviour characterized by
activity during the night and sleep during the daytime |
nocturnal dissociative disorder | a psychiatric wakefulness disorder (as opposed to a sleep disorder),
superficially similar to sleep-walking, in which sufferers wander
off or act out scenarios while technically awake, but without being
aware and with no subsequent memory of them, usually as a
psychological response to earlier abuse or trauma |
nocturnal groaning | another name for catathrenia |
nocturnal myoclonus | another name for periodic limb movement disorder |
non-24-hour sleep-wake syndrome
(Non-24) | a circadian rhythm sleep disorder, mainly
found among blind people with no light perception, in which the sleep-wake cycle and sleep patterns are totally
desynchronized from the normal 24-hour day and follow a free-running cycle (also
called free-running disorder) |
non-REM sleep (NREM) | non-rapid eye movement sleep, that part of the sleep cycle (subdivided into
3 or 4 sleep stages, ranging
from light sleep to deep slow-wave sleep) in which
little or no eye movement occurs, there is no muscle atonia, and dreams are possible but relatively
rare |
norepinephrine | a neurotransmitter in the autonomic and
sympathetic nervous system affecting blood pressure, etc, and a
stress hormone affecting
parts of the brain that control attention (also called noradrenaline) |
normal hypersomnia | a term sometimes applied to
naturally long sleepers (not necessarily reflecting clinical hypersomnia) |
obstructive sleep apnea (OSA) | the most common form of sleep apnea, in which
breathing during sleep is
disrupted by a physical block to the airflow caused by a collapse
of the soft tissues in the throat and respiratory tract, causing
constant awakenings |
oneiric Darwinism | the dream theory that new ideas may be
created through the generation of random thought mutations during
dreaming, most of which may be discarded as useless, but some of
which may be retained as potentially valuable |
orexin | a neurotransmitter produced in the hypothalamus that regulates
arousal, wakefulness and
appetite, and the lack of which causes narcolepsy (also called hypocretin) |
paradoxical insomnia | genuine complaints of little or no sleep that are not
corroborated by objective evidence of sleep disturbances (a kind of sleep state
misperception) |
paradoxical sleep | another name for REM sleep |
paradoxical therapy | a psychological approach to insomnia treatment, which
asks the insomniac to do the exact opposite of trying to fall
asleep, in an attempt to eliminate any subconscious resistance to
treatment |
parasomnia | a type of sleep disorder involving abnormal or
unnatural movements, behaviours, emotions, perceptions or dreams during sleep, often involving partial awakenings during the
transitions between sleep and
full wakefulness |
parietal lobe | the central part of the cerebral cortex of the brain,
responsible for bringing together all the different senses of the
brain, and damage to which can lead to a complete absence of dreams) |
periodic limb movement disorder
(PLMD) | a sleep disorder where a sleeper moves
limbs involuntarily during non-REM
sleep, often manifested as quite violent involuntary kicking
during sleep, thus disrupting
normal sleep patterns (also
known as nocturnal myoclonus) |
phase advance | a variation in an individual’s circadian rhythm such that sleep onset and awakening typically occur significantly
earlier than average (e.g. in older people) |
phase delay | a variation in an individual’s circadian rhythm such that sleep onset and awakening typically occur significantly
later than average (e.g. in adolescents and teenagers) |
pineal gland | a small pine cone-shaped gland
near the centre of the brain that produces several important hormones including melatonin |
polyphasic sleep | segmented and broken-up sleep patterns, common in
many animals and still found in many undeveloped or nomadic human
societies (also called polycyclic sleep, and sometimes
referred to as extreme napping when implemented as a planned sleep pattern) |
polysomnography (PSG) | continuous monitoring of multiple
measures of physiological activity during sleep, including brain activity, eye
movement, muscle activity, respiration and heart rhythm (a polysomnogram is the physical output of the process) |
pons | a thick band of nerve fibres in
the brainstem, linking the spinal cord with the forebrain and containing
nuclei dealing with REM
sleep, respiration, swallowing, sense perception and many
other functions |
post-lunch dip | a tendency to sleepiness around
2:00-3:00pm, as a result of a natural dip in circadian alerting system activity, and
not due to the effects of eating lunch (also called the mid-afternoon slump) |
prefrontal cortex | the front part of the brain,
involved in working memory, attention, personality expression,
decision-making, logical reasoning and self-control, notably
inactive during REM
sleep |
primary hypersomnia | hypersomnia symptoms that continue
unabated for months or even years |
primary insomnia | insomnia not due to any specific physical
or mental imbalance, and having no obvious other cause |
prion | a tiny malformed protein capable of infecting organisms in
much the same way as a virus, leading to diseases like BSE in
cattle and fatal familial
insomnia in humans |
progressive dreams | related dreams that occur in a sequence over a
several nights, with one night’s dream continuing where the previous
night’s dream left off |
protein | one of a large class of large and
complex organic macromolecules (including enzymes, hormones, antibodies, hemoglobin, etc),
composed of amino acids, which are essential for the proper
functioning of an organism, including metabolism, the immune system, growth and tissue
repair |
psychophysiological insomnia | insomnia arising from to a variety of
psychological and behavioural stressors and/or environmental and
situational causes |
rebound sleep | lengthened and deepened recovery sleep following a period of sleep deprivation (this may
apply to both REM sleep and slow-wave non-REM sleep) |
recurrent hypersomnia | hypersomnia symptoms that recur several
times during the year, in between periods of relatively normal sleep-wake cycles, sometimes
accompanied by other disorders such as hypersexuality or compulsive
eating |
recurrent isolated sleep
paralysis | another name for sleep paralysis |
recurring dreams | dreams, often having a nightmare quality, that repeat themselves
night after night with little variation, possibly due to some
unresolved conflict depicted by the dream |
REM sleep | rapid eye movement sleep, that part of the sleep cycle characterized by rapid and
random eye movement, high frequency (theta, alpha and even beta) brain waves similar to those during wakefulness, muscle paralysis
or atonia, and frequent and
vivid dreams |
REM sleep behaviour disorder
(RBD) | a relatively rare parasomnia, in which the protective muscle atonia of REM sleep is absent, so that sufferers
try to physically act out their dreams, often suffering (or causing)
physical injuries in the process |
restless legs syndrome (RLS) | a sleep disorder characterized by a
constant urge to move the legs in order to stop uncomfortable or
odd sensations (tingling, creeping, crawling or aching), mainly
during the time before sleep
onset, leading to disrupted sleep |
reticular activating system | a network of neurons in the reticular formation of the brainstem, which is
responsible for regulating alertness and arousal and mediating transitions between sleep and wakefulness (also called the ascending
reticular activating system) |
reverse learning | the theory of dreams, similar to active unlearning, that synapses activated during dreams actually become weakened rather
than strengthened, so that the content of dreams is unlearned and eliminated from
memory |
secondary insomnia | insomnia occurring as a side-effect of
another disease or complaint (e.g. hyperthyroidism, congestive
heart failure, chronic obstructive pulmonary disease, dementia,
pain-related conditions, or other underlying sleep disorders) |
sedative | a sleeping pill or medication that
causes drowsiness, induces sleep
onset, and/or maintains sleep (also called a hypnotic) |
selective mood regulatory
theory | a theory of dreams whereby dreams function to contain and absorb
negative emotional surges, and to expunge them from waking memory,
allowing the dreamer to remain soundly asleep despite the inner
turmoil, while simultaneously working out emotional problems |
serotonin | a neurotransmitter in the central nervous system, derived from tryptophan, involved in sleep, depression, memory and
other neurological processes, as well as in feelings of well-being
and happiness |
sexsomnia | another name for sleep-sex |
shift work | unusual day shifts, evening shifts
or night shifts, in which the constantly changing sleep patterns can disrupt workers’ circadian clocks and
seriously impact the quantity and quality of their sleep (a formal sleep disorder known as shift worker
disorder is sometimes recognized) |
siesta | another name for a nap |
sigma wave | another name for a sleep spindle |
sleep | a naturally-occurring, reversible,
periodic and recurring state in which consciousness and muscular
activity is temporarily suspended or diminished, and responsiveness
to outside stimuli is reduced |
sleep apnea | a potentially life-threatening sleep disorder characterized
by abnormal pauses in breathing during sleep, the most common variant of which
is obstructive sleep apnea (spelled apnoea in England) |
sleep architecture | the structure and pattern of sleep, including overall sleep duration, sleep depth, sleep stages and phases, time spent in non-REM and REM sleep, the organization of sleep cycles, etc |
sleep cycle | the recurring progression of sleep stages, through
different levels of non-REM
sleep to REM sleep and
then back again, repeated four or five times a night |
sleep debt | the cumulative effect of
insufficient sleep, which
leads to mental, emotional and physical fatigue, and problems in
effectively performing day-to-day activities (also known sleep
deficit) |
sleep deprivation | the condition of not having (or
not being allowed to have) sufficient sleep, which leads to sleep debt (also called sleep
loss) |
sleep disorder | any medical disorder which
negatively affects a person’s healthy sleep patterns, to the extent that it
interferes with the person’s normal physical, mental and emotional
functioning (also known as somnipathy or dyssomnia) |
sleep-disordered breathing | any medical condition
characterized by repeated episodes of not breathing (sleep apnea) or under-breathing
(sleep hypopnea) during sleep |
sleep gate | the point encountered during the
late evening when the circadian
drive for arousal falls off, melatonin production increases, and the homeostatic sleep drive becomes dominant enough to allow sleep to occur (also known as the primary sleepiness zone or sleep onset zone) |
sleep hygiene | the practice of consciously
following daily guidelines and adopting particular habits and
routines in order to ensure a more restful and effective sleep |
sleep hypopnea | a sleep disorder similar to sleep apnea, although less common, in
which excessively shallow breathing leads to constant awakenings, as well as loud heavy snoring and choking sounds or
snorts |
sleep inertia | the feeling of grogginess,
impaired alertness and decreased motor dexterity immediately
following awakening |
sleeping sickness | an old name for narcolepsy |
sleep latency | the length of time taken to
transition from full wakefulness to sleep onset, i.e. from “lights out” until sleep (also called sleep
onset latency) |
sleep learning | the memorization of facts,
transference of information or acquisition of new knowledge during sleep, such as by the playing
of audio recordings, etc, now largely discredited as a technique
for enhanced learning (also called hypnopedia) |
sleep-maintenance insomnia | difficulty staying asleep or going
back to sleep once woken
(also known as middle insomnia) |
sleep medication | pills or other medicinal
treatments for transient
insomnia and other sleep
disorders, including benzodiazepines and similar agents, sedative antidepressants,
antihistamines, etc |
sleep medicine | the medical specialty devoted to
the diagnosis and therapy of sleep disturbance and sleep disorders |
sleep onset | the transition from wakefulness into sleep, commonly referred to as “falling
asleep” |
sleep-onset insomnia | difficulty getting to sleep in the first place (also known as initial insomnia) |
sleep paralysis | a parasomnia manifesting as a complete
inability to move or speak during the times of falling asleep or
waking up, due to disrupted REM
sleep and the muscle
atonia that usually accompanies it “leaking” into wakefulness (also called recurrent isolated sleep paralysis) |
sleep pattern | an individual’s overall schedule
of sleep and waking times,
including naps, sleep interruptions, etc |
sleep period | the total time from sleep onset until awakening, including any short mid-sleep arousals,
which may therefore be longer than the actual total time spent
sleeping |
sleep-related eating disorder
(SRED) | a potentially dangerous parasomnia in which the
sufferer sleep-walks to the
kitchen and eats and drinks at random, often including unhealthy
fatty foods, raw foods, strange combinations of foods, or even
toxic substances, cleaning fluids, etc (also called sleep
eating or night eating syndrome) |
sleep restriction therapy | a treatment for insomnia based on very gradually
increasing sleep time, over a
period of weeks or months, from an initial achievable low
level |
sleep-sex | a parasomnia in which sexual acts (from
masturbation and sexual vocalizations to full intercourse and
actual sexual assault) are performed while still asleep and not
remembered afterwards (also called sexsomnia) |
sleep spindle | a short burst of increased brain
activity, in the region of 12-14 Hz, lasting maybe half a second,
typically experienced during stage
2 non-REM sleep (also
known as a sigma wave) |
sleep stages | the different levels and depths of non-REM (stage 1, stage 2 and stage 3) and REM sleep experienced within each sleep cycle, which can be
measured by electroencephalography and represented
graphically by a hypnogram |
sleep start | another name for hypnic jerk |
sleep state misperception (SSM) | the mistaken perception of sleep as wakefulness, leading to severe
underestimates of total sleep time (also known as paradoxical insomnia, pseudo-insomnia or subjective insomnia) |
sleep-talking | a common parasomnia due to transitory arousals from non-NREM sleep or “motor breakthroughs”
during REM dreams, the talk varying from gibberish
or indistinct mumblings to complex monologues and dialogues (also
called somniloquy) |
sleep terror | another name for night terror |
sleep time | the total time spent actually
sleeping during a sleep
period i.e. excluding any short mid-sleep arousals |
sleep-wake cycle | the daily biological pattern of
alternating sleep and wakefulness (roughly 8 hour
of nighttime sleep and 16
hours of daytime wakefulness in humans) |
sleep-wake homeostasis | an internal biochemical system,
mediated by sleep-regulating
substances like adenosine,
that generates a drive or pressure for sleep as a function of the amount of time
elapsed since the last adequate sleep episode |
sleep-walking | a common parasomnia in which sleepers rise from slow-wave sleep and perform
activities usually performed during full consciousness, such as
talking, walking, cleaning, cooking, even driving (also called somnambulism) |
slow-wave sleep | deep non-REM sleep, from which it is difficult
to awaken, characterized by slow delta wave brain activity (also known as deep sleep, delta sleep or stage 3
sleep) |
snore | an involuntary hoarse snorting
sound made during sleep,
caused by vibration of the muscles and soft tissues in the back of
the throat, soft palate and uvula due to obstructed air movement
while breathing during sleep |
somnambulism | another name for sleep-walking |
somniloquy | another name for sleep-talking |
somnipathy | another name for sleep disorder |
somniphobia | another name for hypnophobia |
somnolence | another name for excessive daytime sleepiness or stage 1 non-REM sleep |
spinal cord | a thick cord of nerve tissues
extending through the spinal column, and linking the brain to the
nerves that branch off to other parts of the body |
stage 1 sleep (NREM1) | the first short period of very
light, easily disrupted non-REM
sleep, between wakefulness and sleep proper, characterized by alpha waves and theta waves and often punctuated by
sudden twitches or hypnic
jerks (sometimes called somnolence or drowsy
sleep) |
stage 2 sleep (NREM2) | the second stage of non-REM sleep, and the stage in which
most time is spent, characterized by theta waves punctuated by higher voltage sleep spindles and K-complexes |
stage 3 sleep (NREM3) | the third and deepest stage of non-REM sleep, during which
the sleeper is largely unaware of and unresponsive to the outside
environment, characterized by delta
waves (according to older definitions of sleep stages, where delta sleep accounts for less than 50% of
the total) along with some sleep
spindles (also called deep
sleep or slow-wave
sleep) |
stage 4 sleep (NREM4) | according to older definitions of sleep stages, the deepest
part of slow-wave non-REM sleep, in which delta waves exceed 50% of the
total (also called deep sleep or slow-wave sleep) |
stimulant | a substance, drug or medication
that stimulates the central nervous
system, often used to treat excessive daytime sleepiness |
stimulus control therapy | a treatment for insomnia/span> based on the strict rule that
an individual has just ten minutes to fall asleep and, if sleep is not achieved in that
time, they must get up, go somewhere else to relax, and only return
to bed again when they feel sleepy (also called the 10-minute
rule) |
suprachiasmatic nucleus (SCN) | a tiny region in the hypothalamus of the brain responsible for
controlling circadian
rhythms, sending out the alerting pulses of the circadian alerting system, and regulating melatonin production in
response to the light-dark
cycle |
synapse | an electro-chemical mechanism that
allows neurons to connect to
each other by transmitting and receiving electrical or chemical
signals across a small gap (synaptic gap or synaptic
cleft) between neurons by
means of neurotransmitters (also called synaptic connection) |
teeth grinding | a common parasomnia, often caused by stress or
anxiety, in which teeth grinding during the light stages of non-REM sleep can cause sleep disruption as well as
tooth damage and jaw pain (also called bruxism) |
terminal insomnia | difficulty staying asleep until a
reasonable time in the morning, or waking up very early in the
morning and not being able to get back to sleep (also called late
insomnia) |
thalamus | a region at the base of the brain
through which sensory and motor signals pass to reach the cerebral cortex |
theta waves | brain waves with a frequency of 4-7 Hz
(typical of light non-REM
sleep) |
thyrotropin | a hormone, actively suppressed during sleep, that stimulates the
thyroid gland to produce other hormones used in metabolism (also called thyroid-stimulating hormone) |
transient insomnia | insomnia that persists for just a few
days, usually following a stressful event or excessive use of
caffeine or nicotine |
tryptophan | an essential amino acid (which
must be obtained through diet, such as from chocolate, dairy
products, bananas, nut butters, seeds, etc), which is used to
produce serotonin and melatonin and may help cause
drowsiness |
two-process model of sleep-wake
regulation | the widely-accepted theory,
usually attributed to Alexander Borbély, that sleep is regulated by interactions
between two distinct processes, the circadian rhythm (Process C) and sleep-wake homeostasis (Process S) |
tyramine | a naturally occurring compound,
derived from the amino acid tyrosine (and found in many processed
meats, fermented foods such as cheese, tofu and soy sauce, as well
as in eggplant, raspberries, avocado, nuts, etc), which may have
the effect of inhibiting sleep |
ultradian rhythms | recurrent periods or cycles,
repeated multiple times within a 24-hour period, such as the
repeated sleep cycles within
a full sleep period |
unihemispheric sleep | the ability of some aquatic
mammals and birds to sleep with just one half of their brain at a time, while the other half
(complete with one open eye) remains alert for predators (sometimes
called unihemispheric slow-wave sleep) |
upper airway resistance
syndrome | a sleep disorder similar to, but milder
than, sleep apnea |
ventrolateral preoptic nucleus (VLPO
or VLPN) | a small area in the hypothalamus, sometimes referred to as
the sleep switch because neurons in this area help to promote sleep by inhibiting activity
in areas of the brainstem that maintain wakefulness |
wakefulness | the absence of sleep (sometimes also, in general usage,
alertness or the inability to sleep), in which muscle tone is high, body movement is
voluntary and brain waves are
in the beta and gamma range |
wake maintenance zone | the period, about 2-3 hours before
one’s habitual bedtime, during which the circadian alerting system‘s pulses
emitting from the suprachiasmatic
nucleus reach their peak, offsetting the accumulated homeostatic sleep drive and
allowing for continued alertness late into the evening |
yawn | an involuntary, deep, open-mouthed
inhalation of air, usually during times of drowsiness, fatigue or
boredom |
Zeitgeber | an external environmental time
cue, such as daylight, that synchronizes an organism’s internal circadian clock to the
Earth’s 24-hour light-dark
cycle (from the German word meaning “time-givers”) |
