4.2 Sleep and Why We Sleep

Sleep
- a stated distinguished by low levels of physical activity and reduced sensory awareness.
- it involves interplay between circadian and homeostatic mechanisms, which regulate sleep.
  - our bodies regulate sleep through sleep rebound.
  - sleep rebound refers to the fact that individuals who are deprived of sleep fall asleep more quickly given opportunities for sleep.
- it can be characterized by certain patterns of brain activity, which can be visualized with an EEG.
  - using an EEG, we can also describe and differentiate the different phases for sleep.
Parts of the brain regulate our sleep-wake cycles:
- These parts include:
  - hypothalamus: where the biological clock (the SCN) is located.
  - thalamus: involved in regulation of slow-wave sleep
  - pons: regulates rapid eye movement (REM) sleep
Sleep is also associated with the secretion and regulation of several hormones:
- These hormones include:
  - melatonin:
    - secreted by the pineal gland.
    - regulates biological rhythms and the immune system.
  - FSH and LH:
    - secreted by the pituitary gland.
    - regulates the reproductive system.
  - growth hormone:
    - secreted by the pituitary gland.
    - stimulates physical growth and maturation.
    - regulates other metabolic processes.

There is no clear understanding of the reason for why we sleep.
Several hypotheses explain the idea that otherwise, explain the function of sleep.

First Hypothesis: We might have evolved to sleep in order to restore the resources expended during the day.
- This is derived from the phenomena that bears hibernate during winter when the resources are scarce.
- However, there is little research that supports this idea.
  - It has been suggested that there is no reason to think that our energy demands could not be met with periods of rest and inactivity.
  - Some research found a negative correlation between an individual’s energy demands, and the amount of time spent sleeping.
Second Hypothesis: We sleep as an adaptive response to predatory risk during times of darkness.
- Research on the area is complex and contradictory
  - Research suggests that species that face higher predatory risk sleep fewer hours than other species.
  - Some research suggest that there is no relationship between time for deep sleep and the species’ predation risk.
Third Hypothesis: There is no single universally adaptive function, and different species have evolved different patterns of sleep in response to a species’ unique evolutionary environments.

Fourth Hypothesis: One reason why we sleep is due to its importance to memory formation and cognitive function.
- We know these as sleep deprivation results on memory deficits and cognitive disruptions.
  - This leads to difficulty in maintaining attention, making decisions, and recalling long-term memories.
  - The more sleep deprived you are = the worse these effects become.
- Also, slow-wave sleep after learning a new task can improve performance and store related memory much effectively.
- Optimal sleep has also shown multiple cognitive benefits, such as increased capacities for:
  - language learning
  - creative thinking
  - inferential judgements
  - potential for processing of emotional information.

Across different cultures and periods of time, dreams and their meanings have varied over time,

Austrian psychiatrist Sigmund Freud was convinced that dreams represented opportunities to tap into the unconscious.
By analyzing dreams, Freud though that people can gain insight on how it can help people deal with the problems in their lives.
According to him, he differentiates between the two different meanings of a dream.
- Manifest Content: the actual content, or the storyline, of a dream
- Latent Content: the hidden meaning of a dream.

Swiss psychiatrist Carl Jung believed that dreams allowed us to tap into the collective unconscious.
- This collective unconscious is a theoretical repository of information believed to be shared with everyone.
According to him, certain symbols in dreams are reflected as universal archetypes.
- This means that the meanings of these symbols are similar for all people regardless of culture and location.

Sleep and dream researcher Rosalind Cartwright simply believes that they reflect life events that are important to the dreamer.
- Unlike other perspectives, her idea has found empirical support.
Recent research uncovered techniques on how can researchers detect and classify visual images in their dreams.
- This can be achieved by using fMRI in measuring brain activity patterns.
Neuroscientist John Allan Hobson is credited for the activation-synthesis theory of dreaming.
- He proposes that we dream because our brain tries to make sense (synthesize) the neural activity (activation) that was happening during REM sleep
- This is in contrast to ideas of Freud and others that the meanings of dreams are filled with representations of anxiety, fear, or apprehension.
Recent research continues to update the theory based on accumulated evidence.
- Hobson had also suggested that dreaming represents a state of proto-consciousness.
- This is where dreaming involves constructing a virtual reality in our heads that we might use or might help us during wakefulness.
Hobson has also cited research on lucid dreams to better understand dreaming in general.
- Lucid dreams are dreams where a person becomes aware that they are dreaming and they can control the dream’s content.

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