Module 8.2: Stages of Sleep and Brain Mechanisms

coma

an extended period of unconsciousness with a low level of brain activity

vegetative state

condition in which someone has decreased brain activity and alternates between wakefulness and sleep but shows only limited responsiveness, such as increased heart rate in response to a painful stimulus

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; Physicians usually wait until someone has shown no sign of brain activity for 24 hours before pronouncing brain death

What device enables brain researchers to monitor brain activity during sleep?

an EEG (records an average of the electrical potentials of the cells and fibers in the brain areas nearest to each electrode on the scalp)

polysomnograph

a combination of EEG and eye-movement records

alpha waves

a steady series of brain waves at a frequency of 8 to 12 per second that are characteristic of relaxation (not of al wakefulness)

Label the Polysomnograph Records from a College Student

a. Relaxed, awake

b. Staged 1 sleep

c. Stage 2 sleep

d. Slow-wave sleep

e. Slow-wave sleep

f. REM, or “paradoxical” sleep

stage 1 sleep

the EEG is dominated by irregular, jagged, low-voltage waves; brain activity is less than in relaxed wakefulness but higher than in other sleep stages

stage 2 sleep

prominent characteristics include K-complexes and sleep spindles

K-complex

a sharp brain wave associated with temporary inhibition of neuronal firing

sleep spindle

12 to 14 Hz brain waves in bursts that last at least half a second; results from oscillating interactions between cells in the thalamus and the cortex; increases in number after new learning

slow-wave sleep

sleep occupied by slow, large-amplitude brain waves; heart rate, breathing rate, and brain activity decrease during this time

How are stage 3 and stage 4 distinguished from each other?

Older sources distinguished between stage 3 sleep with fewer slow waves, and stage 4 with more of them.

What do large, slow waves on an EEG indicate?

Large, slow waves indicate a low level of activity, with much synchrony of response among neurons.

paradoxical sleep

sleep that is deep in some ways and light in others; discovered by Jouvet (1960)

rapid eye movement (REM) sleep

sleep stage with rapid eye movements, high brain activity, and relaxation of the large muscles; synonymous with paradoxical sleep; not the same thing as dreaming

non-REM (NREM) sleep

the stages of sleep other than REM

Describe the order of stages of sleep and how long it lasts

• When you fall asleep, you start in stage 1 and slowly progress to stage 2 and then into slow-wave sleep, although loud noises or other intrusions can interrupt the progress. After about an hour of sleep, you begin to cycle from slow-wave sleep back to stage 2 and then REM.

• The sequence repeats, with each cycle lasting about 90 minutes.

The frequency of awakenings correlates with loss of cells in the ___, and with a tendency toward cognitive decline

hypothalamus

How can an investigator determine whether a sleeper is in REM sleep?

Examine EEG pattern and eye movements

During which part of a night’s sleep is REM most common?

REM becomes most common toward the end of the night’s sleep.

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; These neurons receive input from many sensory systems and also generate activity of their own, varying with the circadian rhythm.

How does GABA affect sleep?

it inhibits or interrupts behavior and promotes slow-wave sleep

locus coeruleus

a small structure in the pons that emits bursts of impulses in response to meaningful events, especially those that produce emotional arousal; Axons from the locus coeruleus release norepinephrine widely throughout the cortex, so this tiny area has a huge influence; can promote enhanced attention to important information and enhanced memory

orexin or hypocretin

neurotransmitter that increases wakefulness and arousal; not necessary for waking up, but it is for staying awake

basal forebrain

area anterior and dorsal to the hypothalamus; includes cell clusters that promote wakefulness and sleep

Why do most antihistamines make people drowsy?

A pathway from the hypothalamus uses histamine as its neurotransmitter to increase arousal. Antihistamines that cross the blood–brain barrier block those synapses.

What would happen to the sleep–wake schedule of someone who lacked orexin?

Someone without orexin would alternate between brief periods of waking and sleeping.

How do we remain unconscious in spite of sustained neuronal activity?

• inhibition

• During sleep, axons that release the inhibitory neurotransmitter GABA increase their activity, interfering with the spread of information from one neuron to another. Connections from one brain area to another become weaker. When stimulation doesn’t spread through the brain, you don’t become conscious of it.

What’s an example of some brain areas being awake, while others are asleep?

Sleepwalkers are asleep in much of the brain, but awake in the motor cortex and a few other areas

What would happen to sleeping and waking if you took a drug that blocked GABA?

You would remain awake, or at least somewhat conscious. (Tranquilizers put people to sleep by facilitating GABA.)

Someone who has just awakened sometimes speaks in a loose, unconnected, illogical way. How could you explain this finding?

People often awaken from a REM period, because REM is abundant toward morning when people usually awaken. Different brain areas don’t wake up all at once. Shortly after awakening, certain brain areas may still be in a REM-like state, and thinking may have an illogical, dreamlike quality.

What were the results of researchers using a PET scan to determine which brain areas increased or decreased their activity during REM?

• During REM sleep, activity increased in the pons (which triggers the onset of REM sleep) and the limbic system (which is important for emotional responses).

• Activity decreased in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex but increased in parts of the parietal and temporal cortex.

• REM sleep is associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves, for pons-geniculate-occipital

PGO waves

pons-geniculate-occipital waves; a distinctive pattern of high-amplitude electrical potentials that occur first in the pons, then in the lateral geniculate, and then in the occipital cortex

insomnia

inadequate sleep

How does sleep deprivation affect a person?

Sleep deprivation impairs memory, attention, and cognition. It also magnifies unpleasant emotional reactions and increases the risk of depression

phase delayed

a person has trouble falling asleep at the usual time, as if the hypothalamus thinks it isn’t late enough

phase advanced

a person falls asleep easily but awakens early

sleep apnea

impaired ability to breathe while sleeping; People with sleep apnea have multiple brain areas that appear to have lost neurons, and consequently, many of them show deficiencies of learning, reasoning, attention, and impulse control

What kinds of people are most likely to develop sleep apnea?

Sleep apnea is most common among people with a genetic predisposition, old people, and overweight middle-aged men.

narcolepsy

a condition characterized by frequent periods of sleepiness during the day; strikes about 1 person in 1,000; has 4 main symptoms (a person does not need to have all 4)

What are the four symptoms of narcolepsy?

1. Attacks of sleepiness during the day.

2. Occasional cataplexy—an attack of muscle weakness while the person remains awake. Cataplexy is often triggered by strong emotions, such as anger or great excitement. (One man suddenly collapsed during his wedding ceremony.)

3. Sleep paralysis—an inability to move while falling asleep or waking up. Many people have experienced sleep paralysis at least once or twice, but people with narcolepsy experience it frequently.

4. Hypnagogic hallucinations—dreamlike experiences that the person has trouble distinguishing from reality, often occurring at the onset of sleep.

Whats the cause of narcolepsy?

• The cause relates to the neurotransmitter orexin. People with narcolepsy lack the hypothalamic cells that produce and release orexin.

• Why they lack them is unknown, but the most likely possibility is an autoimmune reaction, in which the immune system attacks part of the body—in this case, cells with orexin

What’s a treatment for narcolepsy?

The most common treatment is stimulant drugs such as methylphenidate (Ritalin), which enhance dopamine and norepinephrine activity.

What is the relationship between orexin and narcolepsy?

Orexin is important for staying awake. Therefore, people or animals lacking either orexin or the receptors for orexin develop narcolepsy, characterized by bouts of sleepiness during the day.

periodic limb movement disorder

a sleep disorder characterized by repeated involuntary movement of the legs and sometimes the arms; mostly during NREM sleep

REM behavior disorder

a condition where move around vigorously during their REM periods, apparently acting out their dreams. They frequently dream about defending themselves against attack, and they may punch, kick, and leap about. They often injure themselves or other people and damage property

What’s a proposed cause for REM behavior disorder?

the results suggest that inadequate inhibitory transmission may be responsible for REM behavior disorder

night terrors

experiences of intense anxiety from which a person awakens screaming in terror; more severe than a nightmare; occurs during NREM sleep and are more common in children than adults; dream content, if any, is usually simple, such as a single image; runs in families; most common during slow-wave sleep early in the night and usually not accompanied by dreaming

Of the following, which shows the LEAST brain activity?

a. Slow-wave sleep

b. Coma

c. Vegetative state

d. Minimally conscious state

b. Coma

Sleep spindles in stage 2 sleep appear to be important for which of the following?

a. Consolidation of memory

b. Inhibition of impulses

c. Defense mechanisms against anxiety

d. Control of body temperature

a. Consolidation of memory

What do the high-amplitude slow waves of slow-wave sleep indicate?

a. An increased level of brain activity

b. Synchrony among neurons

c. Muscle contractions

d. Responses to sensory stimulation

b. Synchrony among neurons

Why is REM sleep also known as paradoxical sleep?

a. Activity in the left hemisphere does not match the activity in the right hemisphere.

b. We did not know it existed until its discovery in the 1950s.

c. It is deep sleep in some ways and light in others.

d. Because a pair of docs discovered it.

c. It is deep sleep in some ways and light in others.

At which time, if any, is slow-wave sleep most common?

a. Immediately after falling asleep

b. Not immediately, but during the early part of the night’s sleep

c. Near the end of the night’s sleep

d. During all parts equally

b. Not immediately, but during the early part of the night’s sleep

What tends to activate the locus coeruleus?

a. Stomach contractions

b. Conflict between emotions

c. Meaningful information

d. Sexual desire

c. Meaningful information

What is the role of orexin with regard to wakefulness and sleep?

a. It stimulates REM sleep.

b. It inhibits the spread of brain activity while someone is asleep.

c. It helps someone stay awake.

d. It is active during switches back and forth between wakefulness and sleep

c. It helps someone stay awake.

Why are people unconscious during slow-wave sleep?

a. Inhibitory transmitters block the spread of activity in the cortex.

b. The sensory receptors become unresponsive to nearly all input.

c. Spontaneous activity ceases in the neurons of the cortex.

d. Circulating hormones block the sodium gates in axon membranes.

a. Inhibitory transmitters block the spread of activity in the cortex.

If you awaken but find you temporarily cannot move your arms or legs, what is happening?

a. You are probably developing a severe neurological disease.

b. You are probably just being lazy.

c. You need more time to get the blood flowing to your muscles.

d. Most of your brain is awake, but part of your pons and medulla remain in REM sleep.

d. Most of your brain is awake, but part of your pons and medulla remain in REM sleep.

Of the following, which one is not associated with an increased probability of sleep apnea?

a. Having a relative with sleep apnea

b. Being female

c. Being overweight

d. Being middle-aged

b. Being female

Narcolepsy is linked to a deficit of which neurotransmitter?

a. Dopamine

b. GABA

c. Orexin

d. Acetylcholine

c. Orexin