Evolutionary Functions of Sleep: Energy, Predation, and Cognition

What are the main risks associated with sleep for animals?

Immobility, vulnerability to predators, and missed opportunities for feeding or mating.

From an evolutionary perspective, what must any trait that persists confer?

Survival or reproductive advantages sufficient to outweigh costs.

What are the two interacting processes that regulate sleep?

The homeostatic drive, which accumulates sleep pressure during wakefulness, and the circadian clock, which gates the timing of sleep.

How often do sleep cycles through NREM and REM occur?

Roughly every 90 minutes.

What are the three stages of NREM sleep?

Drowsiness, light sleep with spindles, and slow-wave sleep.

What characterizes REM sleep?

Desynchronized EEG, vivid dreaming, and muscle atonia.

What evolutionary explanation does energy conservation provide for sleep?

During NREM sleep, core body temperature and metabolic rate decline, reducing caloric expenditure when foraging is risky. (Siegel)

Why can't energy conservation alone explain the persistence of REM sleep?

REM sleep can be metabolically costly, similar to quiet wakefulness.

How does predator avoidance influence sleep patterns in different species?

Species with high predation risk tend to sleep lightly and in short bouts, while apex predators enjoy longer, deeper sleep. (Allison and Cicchetti)

What is the 'sentinel theory' proposed by Taylor et al (2000)?

REM evolved to interrupt long periods of deep NREM, allowing for brief arousals to monitor the environment. (Taylor et al)

What restorative functions does slow-wave sleep support?

Immune function, tissue repair, and synaptic downscaling. (Tononi and Cirelli)

What role does REM sleep play in synaptic connections?

It may prevent the decay of synaptic connections that would deteriorate without intermittent activation.

What argument did Kavanau (1997) make regarding cognitive processing and sleep?

As nervous systems grew complex, it became necessary to have time to organize and store information instead of constantly reacting to the outside world.

What is 'restful wake' and its significance in the evolution of sleep?

Characterized by slowed EEG, it allowed early organisms to stabilize learned information, eventually differentiating into NREM and REM.

How do NREM and REM support different types of memory?

NREM supports the replay and integration of hippocampal-dependent memories, while REM reinforces motor perceptual circuits.

What is the significance of unihemispheric NREM in dolphins and white whales?

It allows them to sleep while still being able to swim, as motor-circuit consolidation is unnecessary due to constant motion.

How does the presence of REM sleep reflect convergent evolution?

Both birds and mammals retained REM sleep to support complex visual and motor demands.

What is the relationship between sleep and recovery according to Siegal (2008)?

The relationship is complex and varies across species, indicating that sleep is not purely restorative.

What does the term 'sleep pressure' refer to?

The accumulation of the need for sleep during wakefulness.

What are the implications of sleep cycles being consistent across mammals and birds?

It suggests that different phases of brain and body activity during sleep have been favored by evolution for survival.

What is the role of the circadian clock in sleep regulation?

It gates the timing of sleep to optimal periods.

What does the term 'muscle atonia' refer to in the context of REM sleep?

A state of temporary paralysis of most voluntary muscles during REM sleep.

What evidence supports the idea that sleep evolved as a multifaceted process?

The combination of energy conservation, predator avoidance, physiological restoration, and cognitive processing.