4 - Sleep in Other Species

Question 1

The fundamental architecture of cortices is the same for most mammals (eg. mice, cats and rats etc.). Why is this important for sleep research?

Answer 1

EEG recordings are relevant and meaningful

Question 2

What is the hyperstriatum? What is its relevance to sleep study?

Answer 2

Area of avian brain derived from the same structure as the mammalian cortex, but has more of a nuclear structure.

These nuclei seem to have similar function to mammalian cortex. Can still record EEG that doesn’t look radically different from mammalian EEG.

Awake/alert bird: low voltage activity
Asleep bird: high voltage activity

Question 3

How is birds REM sleep?

Answer 3

Very brief compared to mammals.

Question 4

Do reptiles, amphibia and fish have cortex/hyperstriatum?

Answer 4

No, no similar cerebrum to mammals/birds

Question 5

What do recordings from reptile/amphibian and fish show?

Answer 5

Homeostatic regulation of sleep

• Low voltage activity = alert
• High voltage activity = sleep

Nothing resembling REM sleep, but slow wave sleep looks a little similar (but may not be)

Question 6

Why do vertebrates all have sleep?

Answer 6

The brainstem is fairly conserved

Question 7

How did people study sleep in invertebrates?

Answer 7

Behavioural criteria

Nervous system too different for electrophysiological recordings.

Question 8

What did Zeppelin contribute to animal sleep study?

Answer 8

4 behavioural criteria for being asleep

Question 9

What are 5 behavioural criteria for being asleep?

Answer 9

• Organism moves to location (usually safe) from where it is usually active and organism positions themselves in a species-specific manner (eg. flamingos standing on one leg in water with head tucked under wing)
• Immobility
• Change in threshold for responding to external stimulus
• A strong enough (moderately intense) external stimulus has to lead to rapid reversal of state to full waking
• If you deprive the organism of the opportunity to engage in above behaviours, you get an increase in pressure to induce state and an increase in amount of time getting it (homeostatic regulation)

Question 10

How do you tell if an animal is actually asleep versus resting?

Answer 10

If the threshold to respond isn’t elevated, it isn’t sleep.

Eg. Waking up immediately at a fire alarm could indicate resting

Question 11

What are a few things that you might mistake for sleep? (4) How can you tell these from sleep?

Answer 11

• Coma (find a threshold where they will wake up, if they don’t wake they’re not asleep)
• Drug induced stupor (find a threshold where they will wake up, if they don’t wake they’re not asleep)
• Hibernation
• Resting (threshold to respond to external stimuli)

If you get someone out of coma or drug induced sleep, they will not try to get back into coma/stupor (last criteria for homeostatic regulation)

Question 12

What is the most critical test for being asleep?

Answer 12

If the state in question is withheld, the organism will try to get it and get more of it.

Question 13

How do we know drosophila sleep?

Answer 13

• Get into unique position with wings
• Don’t move
• Change in threshold for response
• Can be woken with moderate stimulus
• When deprived of state, they try to get more

Question 14

How do you keep drosophila awake?

Answer 14

Keeping them moving/flying

Question 15

When you keep a fruit fly flying, does it stay still because it’s sleeping or because it’s low on calories?

Answer 15

We don’t know because we can’t keep a drosophila awake without keeping them moving

Some genes that regulate sleep in drosophila are very similar to those in humans, shows that some elements of fruit fly sleep are probably similar to mammalian sleep

The ambiguity in answering this question violates the last criteria for sleep (homeostatic regulation).

Question 16

There are placental mammals, marsupials and ___

Answer 16

monotremes (prototheria)

• Including the duck billed platypus and shorty-beaked echidna
• Don’t give live birth (lay eggs)
• Regulate temperature same way as other mammals, but at much lower temperature
• Completely different amounts of REM sleep

Question 17

What do monotremes show in terms of sleep?

Answer 17

• Platypus shows more REM sleep than any other specie studied

Question 18

What is REM sleep defined as for monotremes? Who proposed an explanation of this?

Answer 18

• Atonia
• Rapid eye movement
• Slow waves (weird)

Lesku proposed that this may be an intermediate stage of REM sleep evolution as we know it.

Called brainstem REM sleep, no forebrain indication of REM sleep

Lesku showed a species of bird with brainstem REM sleep but slow waves (ostrich). Ostrich is a very primitive form of bird descendant.

In each of these lineages (birds/mammals), the initial state of sleep was slow waves, periodically SWS interrupted by fast wave sleep.

As the hyperstriatum became more sophisticated, makes it mal-adapted to maintain slow wave sleep for long amount of time.

Result is forebrain now gets a burst of desynchronized cortex.

All this is speculation, but fits with facts.

Question 19

What is unihemispheric sleep? In which
species is it observed and what other unusual (for mammals) sleep characteristic is
observed in these species?

Answer 19

The capacity for some species to show electrophysiologically defined sleep i one cerebral hemisphere while the other hemisphere remains awake

• This type of sleep can typically accompany motor system control, such as active swimming. It is also surprising that they only show medium to high voltage EEGs (SWS in terrestrial mammals)
• Bottlenose dolphin,

Question 20

True or false, if unihemispheric sleep animals are deprived of sleep in one hemisphere, will they try to compensate this?

Answer 20

The other side will not try to compensate this, but during a recovery period, the deprived hemisphere will compensate with delta wave rebound.

Question 21

Describe the sleep patterns of the amphibious fur seals (Otariidae) and true seals (Phocidae) when they are on land and in the sea.

Why?

Answer 21

True seal: Bilateral sleep when submerged in water and waking when they need to breathe

Amphibious Fur Seals: Unihemispheric sleep when submerged, but bihemispheric sleep when on land. This is because of breathing and swimming (contralateral fin). If fur seals are deprived of bihemispheric sleep, they will attempt to get both more unihemispheric sleep and bihemispheric sleep.

Fur seals seem to prefer bihemispheric sleep and have an increased drive for it that true seals do not.

Question 22

What functional advantages of unihemispheric sleep are suggested by results from a study by Rattenborg et al. (1999) of sleep in ducks?

Answer 22

• The choice between uni- and bihemispheric sleep appears to be modulated by the potential for predatory threats.
• Four mallard ducks that were housed in a linear arrangement of four transparent boxes showed different sleep patterns depending on their positions in the row.
• The two central birds that were surrounded by conspecifics on either side tended to show primarily bilateral sleep and bilateral eye closure. The two ‘edge’ birds showed a 150% increase in unilateral sleep and eye closure relative to central birds.

Question 23

How do levels of acetylcholine change in the hemispheres of fur seals when they enter unihemispheric and bihemispheric sleep?

Answer 23

In fur seals, both hemispheres showed depressed ACh levels during bihemispheric sleep (as expected), but only the sleeping hemisphere showed reduced ACh during unihemispheric sleep; the waking hemisphere continued to show high ACh levels, typical of waking in terrestrial mammals

Question 24

What anatomical correlates are there of the presence of unihemispheric sleep? (2)

Answer 24

• Smaller corpus callosum (less connection between two hemispheres)
• Larger posterior commissure (counterintuitive because of above)

Question 25

Describe three major potential advantages of being capable of generating unihemispheric sleep in ocean-dwelling species.

Answer 25

• Permitting sustained sleep in one hemisphere while allowing motor behaviours for swimming and surfacing (to breathe)
• Maintaining close contact with others and vigilance for predators
• Thermal balance, they cannot afford the lost heat production they would suffer if they were to become immobile during sleep, as terrestrial mammals do, and especially if they underwent the atonia of REM sleep.

Question 26

Which two aspects of temperature regulation may be aided by the existence of unihemispheric sleep?

Answer 26

• Motor activity

- Glial thermogenesis

Question 27

What are the implications of the existence of unihemispheric sleep for our use of the usual behavioural criteria for identifying sleep?

Answer 27

• May not adopt unique posture for sleep
• May not reduce or stop gross motor activity
• May not be reduction in environmental responsiveness from one hemisphere

Question 28

How does the existence of unihemispheric sleep in some species change one’s view of the level at which sleep duration is regulated?

Answer 28

Thus, the sleep of aquatic species can be interpreted as meeting most of the usual behavioural criteria for sleep, but doing so only one hemisphere at a time. This conclusion raises interesting questions about the neural level at which sleep homeostasis is regulated, and, as a consequence, the neural level at which the need for sleep arises and is satisfied.

Question 29

How does sleep change during their seasonal migrations for many small migratory
bird species?

Answer 29

• Normally diurnal birds can migrate at night
• Migratory birds develope zugunruhe (migratory restlessness), increased activity orientated towards migration direction (even in cage).
• Reduced sleep by increased activity