Midterm Review and Study Questions

Question 1

What features of human sleep make it particularly difficult to understand why we sleep, from the perspective of evolutionary advantage?

Answer 1

• Sleep is irresistible drive with no obvious survival function
• Sleep entails survival risks
• Lost time (opportunity cost)
• No explanation for dreams

Question 2

What did the results of von Economo’s studies suggest about the nature of neural regulation of sleep that was contrary to the prevailing view at the time of his work in the 1920’s?

Answer 2

Encephalitis enlargica, sleep came from the brain, not toxins in the body.

Question 3

How did Loomis characterize sleep stages during the 1930s, and how do these stage descriptions compare to the standard stage descriptions that were developed decades later?

Answer 3

Loomis et al. classified sleep into five different stages, A to E, based on EEG characteristics. However they failed to identify REM sleep (rapid eye movement sleep). Stage A: drowsy sleep; B: sleep onset C: light sleep; D: intermediary sleep and E: deep sleep. Stage B corresponds to sleep stage 1 of the contemporary classification

Question 4

Summarize the principal findings made by Bremer using the encéphale isolé and cerveau isolé preparations. How do these finding relate to the traditional view of the factors that generate waking and sleep?

Answer 4

That sensory input carried be the cranial nerves was necessary in order to arouse the cortex to wakefulness.

Question 5

How did the studies of Moruzzi and Magoun related to the Ascending Reticular Arousing System (ARAS) contribute to our understanding of how sensory input affects arousal?

Answer 5

Many lesions in cats (decorticalization etc.). The researchers proposed that a column of cells surrounding the midbrain reticular formation received input from all the ascending tracts of the brain stem and relayed these afferents to the cortex and therefore regulated wakefulness.

Question 6

What were Sigmund Freud’s views related to dreams and their function. How did his views both differ from and continue some ancient traditions related to the source of dreams and their interpretation?

Answer 6

His belief that dreams represent disguised messages (albeit, messages to and from oneself) was consistent with ancient beliefs, but he added the idea that the function of the disguise was to prevent anxiety and arousal that could disrupt sleep

The structure of dreams, and their often obscure and baffling content, were ways of expressing powerful instinctual drives (often sexual in nature) in a safe manner, without causing the dreamer the anxiety of acknowledging these drives, and without allowing their associated arousal to disturb sleep

Question 7

What were the critical findings of Aserinsky, Dement and Kleitman that contributed to the emergence of a new view of the nature of sleep during the mid-20th century?

Answer 7

• Slow rolling eye movements for falling asleep
• REMs accompanied by brain/body arousal
• REM considered an emerging stage, rather than descending (ie. not something one does when falling asleep)

Question 8

What was Jouvet’s early contribution to the study of REM sleep?

Answer 8

• Observed REM sleep in cats
• Called it paradoxical sleep for the complete loss of muscle tone (atonia)
• Attributed the loss of postural muscle tone to descending inhibition of spinal motor systems by a region of the pons

Question 9

What remarkable experimental observation did Jean-Jacques d’Ortous de Mairan make in the 18th century and how did he interpret it?

Answer 9

Found biological rhythms in the mimosa plant

Question 10

What critical observation did de Candolle make in the 19th century that changed the
possible interpretations of de Mairan’s phenomenon?

Answer 10

Candolle put the mimosa plant in constant light and found that it was phase shifted two hours earlier. Light was made responsible for this (early evidence for entrainment)

Question 11

If you observed a daily rhythm of water intake in a new organism you had discovered, how would you go about determining whether that is a true circadian rhythm or not?

Answer 11

Force a phase shift, if there is entrainment to the shift than you can say the rhythm is circadian (near 24 hours)

Question 12

Based on the work of DeCoursey, Pittendrigh and others, what is the standard model of how an external 24 h cycle can entrain rhythms with periods that differ in both directions from 24 h?

Answer 12

Giving light pulses to free runing organisms caused phase delays (lengthening period by one cycle) or phase advances (shortening the period by one cycle)

Because of the mechanics of entrainment, short-period clocks tend to become stably synchronized at an early phase relative to the external cycle (phase lead) while long-period clocks tend to be relatively late (phase lag)

Question 13

At a neuronal level, how can we interpret the fact that an awake, alert individual shows a desynchronized EEG characterized by low-voltage, fast activity?

Answer 13

Many neurons are being excited and inhibited at the same time, so the sum is close to zero.

Question 14

When the neuronal population being recorded is relatively synchronized, the EEG will be characterized by?

Answer 14

High voltage slow oscillations (HVS)

Question 15

A desynchronized neural population will generate?

Answer 15

unstable, low-voltage, fast oscillations (LVF) in the EEG record

Question 16

How is Fourier analysis used in the evaluation of EEG signals related to the study of sleep?

Answer 16

Fourier analysis yields a power spectrum, which illustrates how much power (weighting) is associated with each frequency contributing to any given waveform

Question 17

What are the four frequencies related to sleep and waking?

Answer 17

β : beta: >13
α : alpha: 8-13
θ : theta: 4-8
δ : delta: 1-4

Question 18

What type of neurons in the brainstem play a role in the onset of REM sleep?

Answer 18

Cholinergic pontine (pons) neurons

Question 19

What are the two greatest disadvantages of actigraphy?

Answer 19

Actigraphy is not useful for distinguishing sleep stages, since gross motor patterns alone cannot discriminate all sleep stages, nor can it be used to detect symptoms of most sleep disorders.

Question 20

What are masking effects?

Answer 20

This term refers to the idea that external stimuli that alter behaviour directly, rather than by acting through the circadian system, can mask or obscure the actual state of the circadian system at that time. Because overt, measurable rhythms in behaviour or physiology are used as an index of the activity of the underlying circadian clock mechanism that drives them, anything external to the organism that modifies an overt rhythm can complicate assessment of the state of the underlying circadian system.

Question 21

What are positive and negative masking effects?

Answer 21

activity provoked by an external noise may cause an animal to behave as if it were in its active phase, even when its circadian clock is dictating rest. This is an example of positive masking, the induction of a behaviour at an inappropriate circadian phase. When an environmental change instead inhibits behaviour that would normally occur at that time (e.g., putting a cover over a canary’s cage during the day so that it stops singing), it is considered an example of negative masking.

Question 22

Who conducted the first systematic studies of human circadian rhythms in a
laboratory?

Answer 22

Jürgen Aschoff and Rütger Wever

Question 23

Why is temporal isolation a critical condition for many studies of circadian rhythms?

Answer 23

To prevent masking effects

Question 24

What is the phenomenon of different rhythms running with different periods? What did this method show about circadian rhytms?

Answer 24

Spontaneous internal desynchronization

It provided some of the earliest evidence suggesting that more than one circadian clock was involved in the regulation of human daily rhythms.

Question 25

What is a constant routine and how is it used to study circadian rhythms?

Answer 25

The idea underlying this approach is that even in temporal isolation people may be exposed to events that can affect the measurement of the output of the circadian clock. For example, large meals can affect body temperature, so the pattern of the daily temperature rhythm could be modified by the meal pattern selected by a participant. An individual’s own postural changes may influence measurement of body temperature or hormonal rhythms, and increased activity can raise body temperature. Going to sleep can also lower temperature and affect other rhythms independently of the circadian system. All of these effects can be seen as types of internal masking. This term refers to masking effects on a target measure that result from the participant’s own behaviour, rather than from an external disturbance. Thus, if one wants a pure measure of the waveform and periodicity of a human body temperature rhythm, for example, one has to control not only the environment but the individual’s own activity, posture, meal patterns and other behaviours.

Question 26

What is forced desynchronization and how is it used in studying the regulation of
human sleep?

Answer 26

By forcing sleep to occur at many different circadian phases, rather than solely during the usual circadian rest phase, one can evaluate what the independent impact of the circadian system is on features such as sleep onset, sleep duration, and REM sleep or SWS probability

This approach depends on the fact that circadian clocks cannot be synchronized to external cycles that differ very much from the natural, or intrinsic, period of the clock. Thus, if participants in a time-free environment are signalled to sleep and awaken cyclically with period lengths of, e.g., 21 or 28 h, their near-24 h circadian clocks cannot follow these cycle lengths, even if the sleep-wake cycle does

Question 27

What are the principal advantages and disadvantages of studying circadian rhythms
in a controlled laboratory environment? Similarly, what are the advantages and disadvantages of studying them in the field environment?

Answer 27

• Some of the factors that are held constant or eliminated in laboratory studies may have very important roles in shaping circadian rhythm expression in the natural world
• Controlled conditions allow for replication

Question 28

List the stages of sleep a healthy adult human goes through in their first cycle

Answer 28

• Stage 1 (briefly)
• Stage 2 (10-25 min)
• Stage 3/SWS (25-45 min)
• Stage 2 (few minutes)
• REM (around 5 min)

Question 29

How long are average sleep cycles in humans?

Answer 29

90-110 minutes

Question 30

What is a Basic Rest-Activity Cycle and what is the evidence that it exists?

Answer 30

NREM/REM cycles continuing into daytime activity.

Evidence:

• Oral activity rhythms
• Cognitive performance

Question 31

What are the infant equivalents for NREM and REM sleep called?

Answer 31

NREM: Quiet sleep
REM: Active sleep

Question 32

How long is a newborn’s REM/NREM cycle?

Answer 32

50-60 minutes cycles

Question 33

What proportion of newborn’s sleep is REM?

Answer 33

50%

Question 34

True or false? Changes in white matter can be attributed to myelination in both girls and boys.

Answer 34

False

Only in girls

Question 35

What underlying circadian clock change may contribute to the altered sleep timing of adolescents?

Answer 35

related to modifications (so far unidentified) in hormonal or neural mechanisms that regulate the circadian clock. Based on oscillator theory, a lengthened internal circadian period would predict delayed (i.e., later) preferred sleep onset and sleep end times

Question 36

What molecular biological mechanism might explain longterm preferences for a delayed sleep phase?

Answer 36

Polymorphisms in the PER3 and CLOCK genes

Question 37

What mutated gene binds to PER2 to induce a longterm preference for advanced sleep phase?

Answer 37

Casein kinase 1 delta

Question 38

How is REM sleep in the platypus and ostrich unique?

Answer 38

REM sleep (eye movement and atonia) accompanies slow waves

Question 39

What are the two evolutionarily distinct types of REM sleep?

Answer 39

• Brainstem REM sleep (ostriches and platypus)
• Forebrain REM sleep (brainstem REM is accompanied by cortical activation)

The forebrain REM sleep feature of cortical activation was
Chapter 4. Sleep in other species 73
added to create the paradoxical situation of cortical activation occurring during continued sleep.

Question 40

What is an explanation for evolution from brainstem REM to forebrain REM?

Answer 40

One possibility is that the evolution of the mammalian cortex (and its avian counterpart, the hyperstriatum) made it maladaptive to maintain lengthy periods of synchronized slow waves during sleep. Perhaps the development of a more complex cortical organization to facilitate a growing capacity for learning and brain plasticity throughout life.