Sleep and Dreams

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Sleep and Dreams

• AWAKE Group Presentation
• May 2, 2007
• Victoria Zvonkina, M.D.

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Dreams

• Dreams have fascinated people for centuries.
• The reasons why dreams occur are still obscure.
  When something is not clear, there is always room
  for speculation.
• Dream interpretation is still very popular.
• Internet has many dream interpretation websites (
  example below).

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Why We Dream

• The search for an understanding of dreams is
  thousands of years old.
• Yet to this day there are disagreements between
  researchers.
• Over the past 100 years, three theories dominated
  research
• - Late 19th century, Freuds Interpretation of
  Dreams
• - 1950s report of correlation of dreaming and
  newly discovered rapid eye movement (REM) sleep
• - 1970s theory that dreaming was triggered by
  random neural activity in the brainstem.
• New approach to dreaming is to consider it as a
  memory processing mechanism.

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Brain Activity During Sleep

• To understand how dreams may be produced and
  their functions, it is important to understand
  how brain activity differs in wake and REM and
  non-REM sleep.
• A series of positron emission tomography (PET)
  studies showed that most brain regions are
  inactive during slow wave sleep, entry into REM
  leads to reactivation of some regions, along with
  deactivation of others.
• This pattern in REM suggests a shift away from
  conscious executive control and towards
  hallucinatory (activation of sensory association
  cortices) and emotional (activation of amygdala,
  anterior cingulate, and medial orbitofrontal
  cortex) processing.

Maquet P, 2001 Hobson et al, 1998 Nofzinger EA
et al, 1997.
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Sleep and Memory Processing

• Sleep has been shown to enhance prior learning of
  perceptual and motor skills, paired word
  associates, and emotionally charged episodic
  memories.
• In humans, positron emission tomography (PET)
  studies have shown that brain regions activated
  during learning a task were selectively
  reactivated during the next nights REM sleep
  (Maquet P, et al, 2000.)
• In rats, similar results were shown as well
  (Louie K, Wilson MA, 2001.)

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Memory Consolidation

• Not all sleep is equal in relation to learning
  and memory consolidation.
• For example, improvement on a motor skill task
  has been reported to correlate with amounts of
  late night light (stage 2) Non-REM sleep (Walker
  et al, 2002), but improvement on a visual
  perception task to correlate with both late-night
  REM sleep and early-night slow-wave Non-REM sleep
  in separate studies (Stickgold R, 2000 Karni A
  et al, 1994.)

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Memory Consolidation cont.

• If memory processing in sleep is differently
  activated during sleep stages, and dreaming at
  least parallels, and possibly contributes to
  these processes, then we would expect to see
  changes in the dream content during different
  sleep states.
• Simply put, this is exactly what is seen.
• In REM sleep, dreams are hallucinatory,
  emotional, narrative, and with frequent fictive
  movements. It is thought to facilitate
  consolidation of visual perceptual and emotional
  memories.
• Non-REM sleep is more thought-like and less
  hallucinatory, and is implicated in in simple
  memorization (word pair lists experiments).

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Memory and REM sleep

• One experiment focused on incorporation of waking
  events into the dream content (Fosse MJ, 2003.)
• Out of 299 dream reports, there were 364 waking
  dream elements.
• However, only 1-2 of these appeared as possible
  replay of waking events.
• Therefore, we dream about what happened, but not
  what actually happened. (Strickgold R, 2003.)

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Incorporation of Waking Events Into Dreams

• Another experiment involved subjects palying a
  game of Tetris 2-3 hrs for 2 or 3 days.
• Subjects 12 subjects with no prior Tetris
  experience novices 10 with extensive Tetris
  experience experts and 5 subjects with dense
  amnesia with extensive medial temporal lobe
  damage from either anoxia or encephalitis
  amnesiacs.
• On the evening of each day of game play subjects
  were awakened repeatedly during the first hour of
  night, and asked to recall thoughts, feelings, or
  images from sleep.
• Nine of the novices, and five of the experts (a
  total of 64) reported visual images of the game
  at sleep onset.
• 60 of amnesiacs also reported images from the
  game, however they could not recall playing the
  game due to amnesia.
• The reports were similar between the groups, such
  as seeing little squares going down the screen,
  and occasionally rotating them but none reported
  seeing the desk or the room.
• Thus the imagery had no characteristics of
  episodic memories, and it was also limited the
  aspects of the experience to which subjects paid
  most attention.

Strickgold R, et al. Science 2000290350-353.
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Memory and Dreams

• These examples illustrate that memory processing
  indeed occurs during sleep.
• They also show that different types of memories
  are processed differently by the brain.
• Different stages of sleep serve different
  functions in memory processing.

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Dream Content From an Evolutionary Standpoint
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Dream Content From an Evolutionary Standpoint

• There is no unified explanation, what role do
  dreams play, and due to what evolutionary
  pressures they have evolved.
• It seems maladaptive to lose responsiveness to
  the surroundings and experience hallucinations
  instead of real events.
• Sleep however, is an easily reversible state, and
  different stimuli can be sensed strongly enough
  to trigger an awakening.

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Sleep In a Novel Environment

• One evolutionary adaptation is that animals sleep
  in safe sites where they can be less vulnerable
  to attack by predators.
• Therefore, many mammals spend a lot of energy and
  time seeking and protecting sleep sites (Hobson,
  1989.)
• A novel environment can present unknown dangers,
  and individuals will often not have a such a good
  night sleep as in a familiar environment.
• Sleeplessness and fitful sleep that are often
  experienced in a novel environment function to
  provide an opportunity to learn to identify
  external stimuli, which on subsequent nights may
  be ignored (Symons, 1993.)
• Sleep in a novel environment will contain a
  higher number of nocturnal awakenings and a
  shorter latency of REM sleep (Gundel, et al,
  1993.)

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Vigilance Mechanism

• Vigilance hypothesis (Symons et al, 1993) does
  not give any explanation to the function of
  dreams, but it states that natural selection has
  disfavored those hallucinations that compromise
  external vigilance.
• Since the sleeper is unable to see or move,
  vision and movement do not play a role in
  providing accurate information about external
  world. These are non-monitored modalities.
• Therefore, vision and movement hallucinations can
  exist during sleep without compromising vigilance.

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Vigilance Mechanism cont.

• Modalities such as touch, smell, or sound can
  compromise vigilance by interfering with signals
  coming from the external environment.
• These modalities are monitored by the sleeper.

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Vision in Dreams

• Dreams during REM sleep are predominantly visual
  (Hobson, 1988.)
• Some detection of external visual stimulation
  still occurs.
• Gross changes in illumination will cause
  awakening, because they can either signify a
  potential danger, or a suitably timed bright
  light will be interpreted as a circadian cue,
  such as light of dawn (Deacon Arendt, 1994.)
• External light flashes may be incorporated into
  dreams (Dement Wolpert, 1958.)

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Movement in Dreams

• We are generally immobile during sleep, so
  dreaming of movement (similar to dreaming of
  vision) does not compromise vigilance.
• Immobility during sleep is an adaptive mechanism,
  protecting us from ourselves.
• People with narcolepsy often have injuries due to
  sleep walking (Bear et al, 1996.)
• Frequent vestibular activation during REM sleep
  may explain dreams of flying, floating, and
  falling.
• Dreams of falling, however, may trigger awakening
  due to the vigilance theory, because falling can
  occur during sleep unlike other kinds of motion
  (Symons, 1993.)

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Kinesthetic Sense in Dreams

• Kinesthetic sense, or a sense of detecting the
  actual body position, is important to monitor
  during sleep.
• Therefore, there are virtually no dreams with
  kinesthetic sensation in them (Hobson, 1988.)
• Rechtschaffen, one of the fathers of sleep
  medicine, (1973) writes yet it is true that
  someone might sleep through a very exciting
  dream, whereas we would probably not have very
  much difficulty in awakening him by lifting his
  arm.

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Sense of Touch in Dreams

• Sensation of touch is not very often present in
  dreams in order for us to be able to recognize a
  real stimulus.
• Symons (1993) reports frequencies of touch
  sensations in dreams from 1 to 9.
• According to the vigilance hypothesis natural
  selection could not favor vivid dreams of tactile
  sensations, because inability to detect a real
  tactile sensation could compromise survival.
• We have all heard, when a person is wondering
  whether they are sleeping they may pinch
  themselves.

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Sense of Smell in Dreams

• Dreams of smell, or olfaction would also not be
  favored by evolution because they would
  compromise vigilance to real smells.
• Olfactory sensations were reported only in 1 of
  dream narratives (Symons, 1993.)
• The speculation is that a smell signifying a
  known danger should awaken the sleeper.
• However, studies of neutral smells (i.e.,
  peppermint) on sleep show a low percent of
  awakening (Badia et al, 1990.)

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Audition in Dreams

• Sleepers should also be vigilant to external
  noises.
• The data on this subject is contradictory.
• External noises are being well detected by
  sleepers (Degaute et al, 1992 Arkin, 1981.)
• However, 63 of dream narratives contain auditory
  sensations (Symons, 1993.)
• The theory is, that auditory dreams relate
  primarily to speech, but not to other types of
  auditory signals that could compromise survival.

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In Summary

• Sleep research so far has not disproved the
  vigilance hypothesis.
• It explains from an evolutionary standpoint why
  we experience only certain sensation in dreams,
  and not others.
• However, this hypothesis does not explain why we
  dream in a general sense.

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Conclusions

• The leading scientific theory is that sleep has a
  large function in memory processing.
• It appears from different research studies that
  different stages of sleep have different
  functions with respect to memory processing.
• Future research is needed to better identify
  these functions.
• It also remains to be understood, whether dreams
  have a specific function, or are simply a
  byproduct of memory processing in sleep.

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References

• Arkin AM. Sleep Talking Psychology and
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• Badia P, Wesensten N, Lammers W, Culpepper J,
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• Fosse MJ, et al Dreaming and episodic memory A
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• Freud S The Interpretation of Dreams. 1955,
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• Gundel A, Nalishiti V, Reucher E, Vejvoda M,
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• Hobson JA. The Dreaming Brain. 1988, Basic Books.
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References cont.

• Hobson JA, Stickgold R, Pace-Schott EF. The
  neuropsychology of REM sleep dreaming.
  Neuroreport 1998 9R1-R14.
• Karni A, et al. Dependence on REM sleep of
  overnight improvement of a perceptual skill.
  Science 1994 265679-682.
• Louie K, Wilson MA. Temporally structured replay
  of awake hyppocampal ensemble memories during
  sleep. Neuron 2001 29145-156.
• Maquet P, et al. Experience-dependent changes in
  cerebral activation during human REM sleep. Nat
  Neurosci 2000 3831-836.
• Maquet P. the role of sleep in learning and
  memory. Science 2001 2941048-1052.
• Nofzinger EA, et al Forebrain activity in REM
  sleep an FDG PET study. Brain Res 1997
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• Rechtschaffen A. The psychophysiology of mental
  activity during sleep. The Psychophysiology Of
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• Strickgold R Memory, cognition, and dreams.
  Sleep and Plasticity. Oxford University Press,
  2003, pp 17-40.
• Strickgold R, et al. Replaying the game
  hypnagogic images in normals and amnesiacs.
  Science 2000290350-353.
• Strickgold R, et al. Visual discrimination task
  improvement a multi-step process occuring during
  sleep. J Cogn Neurosci 200012246-254.
• Symons D. The stuff dreams arent made of why
  wake-state and dream state sensory experiences
  differ. Cognition 1993 47181-217.
• Walker M, et al. Practice with sleep makes
  perfect sleep dependent motor skill learning.
  Neuron 2002 35205-211.

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Thank You