Glossary
Alpha Waves
Relatively slow brain waves characteristic of a relaxed, but still awake, state, often experienced just before falling asleep.
Example:
As you lie in bed, eyes closed and feeling calm, you are likely experiencing an increase in alpha waves.
Beta Waves
High-frequency, low-amplitude brain waves associated with an alert, awake, and actively thinking state.
Example:
When you are intensely focused on solving a complex math problem, your brain is primarily producing beta waves.
Circadian Rhythm
Your body's natural, internal 24-hour cycle that regulates sleep-wake patterns, body temperature, and hormone release.
Example:
After pulling an all-nighter, your body's natural circadian rhythm will likely be thrown off, making it hard to fall asleep at your usual time the next night.
Delta Waves
Large, slow brain waves associated with the deepest stages of sleep (NREM-3), indicating profound relaxation and reduced brain activity.
Example:
When a person is in a state of deep, restorative sleep, their EEG will primarily show prominent delta waves.
Electroencephalograms (EEGs)
Devices used by neurologists to measure and record the electrical activity of the brain, often used to study sleep stages.
Example:
Researchers used electroencephalograms to observe the distinct brain wave patterns of participants as they transitioned through different sleep cycles.
Hallucinations
Sensory experiences that appear real but are created by the mind, which can occur during the hypnagogic state of NREM-1 sleep.
Example:
Just as he was falling asleep, David experienced a vivid hallucination of someone calling his name, though no one was there.
Insomnia
A common sleep disorder characterized by persistent difficulty falling asleep, staying asleep, or getting a good quality of sleep.
Example:
Despite feeling exhausted, Maria often suffers from insomnia, lying awake for hours before finally drifting off.
Jet Lag
A temporary sleep disorder caused by rapid travel across multiple time zones, disrupting the body's natural circadian rhythm.
Example:
After flying from New York to Tokyo, Sarah experienced severe jet lag, feeling wide awake at 3 AM and exhausted during the day.
Latent Content
According to Freud, the underlying, symbolic, and hidden meaning of a dream, which reveals unconscious drives and conflicts.
Example:
While the manifest content of your dream might be flying on a pizza, the latent content could symbolize your desire for freedom or a feeling of being overwhelmed by choices.
Manifest Content
According to Freud, the remembered storyline or superficial plot of a dream, which is often bizarre or nonsensical.
Example:
In a dream, you might recall the manifest content of flying through the sky on a giant pizza, which is the literal story you remember.
Melatonin
A hormone produced by the pineal gland that helps regulate sleep and wakefulness by increasing in the evening to promote sleep.
Example:
Taking a melatonin supplement before bed can sometimes help people adjust their sleep schedule, especially when experiencing jet lag.
NREM-1 (Hypnagogic State)
The initial, lightest stage of non-REM sleep, characterized by a transition from wakefulness to sleep, where one might experience hallucinations.
Example:
During NREM-1, Sarah felt a sudden jolt as if she were falling, a common sensation in this light sleep stage.
NREM-2
A deeper stage of non-REM sleep characterized by the appearance of sleep spindles and K-complexes, where one is less easily awakened.
Example:
During NREM-2, a sleep study participant's EEG showed distinct bursts of brain activity known as sleep spindles.
NREM-3 (Deep Sleep)
The deepest stage of non-REM sleep, characterized by slow delta waves, where growth hormones are released and the body undergoes significant restoration.
Example:
Children often spend a significant amount of time in NREM-3, which is crucial for their physical growth and development.
Narcolepsy
A chronic neurological condition characterized by overwhelming daytime drowsiness and sudden attacks of sleep, often triggered by strong emotions.
Example:
During an exciting conversation, John suddenly experienced a narcolepsy attack, falling asleep mid-sentence.
Night Terrors
Episodes of screaming, intense fear, and flailing while still asleep, typically occurring during NREM-3 sleep and common in children.
Example:
Unlike a nightmare, a child experiencing night terrors might sit upright in bed, eyes wide open and screaming, but be unresponsive and have no memory of the event later.
Plasticity
The brain's ability to change, adapt, and reorganize itself throughout life, especially in response to experience or damage.
Example:
Learning a new language as an adult demonstrates the brain's remarkable plasticity, as it forms new neural connections.
REM Rebound
The tendency for individuals to spend more time in REM sleep after periods of REM sleep deprivation, as the body tries to catch up.
Example:
After several nights of poor sleep, Sarah noticed she had unusually vivid and long dreams, which is a common sign of REM rebound.
REM Sleep (Paradoxical Sleep)
A stage of sleep characterized by rapid eye movements, vivid dreaming, increased brain activity similar to wakefulness, and temporary muscle paralysis.
Example:
During REM sleep, even though your brain is highly active and you're dreaming vividly, your body's muscles are temporarily paralyzed, preventing you from acting out your dreams.
Sleep Apnea
A potentially serious sleep disorder in which breathing repeatedly stops and starts during sleep, leading to frequent awakenings and poor sleep quality.
Example:
His partner noticed that during the night, Mark would frequently stop breathing for short periods, indicating he might have sleep apnea.
Sleep Deprivation
A condition that occurs when an individual does not get enough sleep, leading to impaired concentration, drowsiness, and negative health effects.
Example:
After studying all night for an exam, Mark suffered from sleep deprivation, making it difficult to focus and recall information during the test.
Sleep Paralysis
A temporary inability to move or speak that occurs just as one is waking up or falling asleep, often accompanied by vivid hallucinations, due to REM sleep mechanisms lingering.
Example:
Waking up unable to move or scream, despite feeling fully conscious, is a terrifying experience known as sleep paralysis.
Sleep Spindles
Sudden, brief bursts of rapid, rhythmic brain wave activity that occur during NREM-2 sleep, thought to be involved in memory consolidation.
Example:
The presence of sleep spindles on an EEG indicates that a person has entered the NREM-2 stage of sleep.
Suprachiasmatic Nucleus (SCN)
A cluster of neurons in the hypothalamus that serves as the primary control center for the circadian rhythm, responding to light cues.
Example:
When light hits your eyes in the morning, the suprachiasmatic nucleus signals your body to reduce melatonin production, helping you wake up.
Theta Waves
Brain waves that are slower than alpha waves, typically present during NREM-1 sleep and also associated with deep meditation.
Example:
As a person drifts off to sleep, their brain activity shifts from alpha waves to the slower theta waves.