Garrett: Brain & Behavior, 2e
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Chapter 15: Sleep and Consciousness
Chapter Summary, Outline, and Key Terms
Brief Chapter Summary:
Chapter 15 is a discussion of sleep, consciousness, and associated issues. The chapter begins
with a description of circadian rhythms and the physiological origins of the 24-hour cycle.
Then rhythms of shorter duration are described, including the basic rest and activity cycle
evident during the day and the cycle seen in the stages of sleep. The electroencephalogram
(EEG) is described as the primary indicator of changing arousal levels during sleep and
waking. Evidence for various functions of rapid eye movement and slow wave sleep are
examined, followed by a summary of the brain structures involved in sleep and waking. This
section concludes by covering sleep disorders and their potential causes and a discussion of
sleep as a form of consciousness. This raises the question of how we define consciousness.
The second part of the chapter continues this exploration by analyzing awareness and
attention as components of consciousness and continues with a discussion of how a sense of
self is achieved and influenced. The roles of body image, memory and mirror neurons within
the sense of self are presented and lead into a section on the disorders of self, specifically the
split brain and dissociative identity disorder. The chapter concludes with a theoretical
discussion of the nature of consciousness.
Outline and Key Terms:
I. Sleep and Dreaming
A. The purpose of sleep is unclear.
1) Restorative Hypothesis
2) Adaptive Hypothesis
B. Circadian Rhythms
1) The suprachiasmatic nucleus (SCN) of the hypothalamus is the main (although not
the only) “clock” controlling the circadian rhythm
(a) Zeitgebers are environmental stimuli that help regulate the sleep/wake cycle
(b) Melatonin is a hormone released by the SCN from the pineal gland which
induces sleepiness
(c) Light information reaches the SCN from the retinohyopthalamic pathway
C. Rhythms During Waking and Sleeping
1) Ultradian rhythms are cycles that are shorter than a day
2) The basic rest and activity cycle is 90-100 minutes long
3) Sleep is measured by electroencephalogram or EEG
(a) Stage 1 is characterized by theta waves
(b) Stage 2 is indicated by the appearance of sleep spindles and K complexes
(c) Stages 3 and 4 are known as slow wave sleep and are characterized by slow delta
waves
(d) Stages then reverse and end with rapid eye movement (REM), instead of
returning to Stage 1
D. The Functions of REM and Non-REM Sleep
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1) The Activation-Synthesis Hypothesis states that during REM sleep the forebrain
integrates neural activity generated by the brainstem with information stored in
memory
2) According to another hypothesis, REM sleep promotes neural development during
childhood
The Functions of Non-REM Sleep
1) Slow wave sleep responds to temperature
2) Slow wave sleep may promote cerebral recovery
Sleep and Memory
1) REM sleep promotes memory (see chapter 12)
2) Both REM and slow wave sleep are needed for consolidation
3) The reverse learning hypothesis states that memories are purged during REM sleep
Brain Structures of Sleep and Waking
1) Sleep Controls
(a) Adenosine accumulates in the basal forebrain and preoptic area during
wakefulness and ultimately induces drowsiness
(b) The preoptic area and pons are particularly important for sleep regulation
2) The basal forebrain contains both sleep-related cells and cells related to waking.
3) Waking and Arousal
(a) Two major pathways
i. PPT/LDT
ii. Locus coeruleus and rahpe to cortex
(b) Arousing pathway includes neurons from the lateral hypothalamus
(c) The pons is the source of PGO waves
i. Excitation travels from the pons through the lateral geniculated to the occipital
area
ii. PGO waves trigger the EEG desynchrony of REM
(d) The pons sends impulses to the magnocellular nucleus to produce the atonia of
REM. Disordered atonia is seen in cataplexy, a form of narcolepsy
Sleep Disorders
1) Insomnia
(a) Insomnia is the inability to sleep or obtain quality sleep
(b) Lack of sufficient sleep can shorten the lifespan and may contribute to obesity
(c) Affected by stress and most common in people with psychological problems
(d) Treatment can be addictive
(e) Disruption of the circadian rhythm, and thus a desynchrony between body
temperature and sleep initiation or time of arousal is often the culprit
2) Sleepwalking
(a) Occurs during slow wave sleep
(b) Can be triggered by stress, alcohol and sleep deprivation
3) Narcolepsy
(a) Narcolepsy patients fall into REM sleep suddenly during waking hours
(b) Mutation of the HLA-DQ6 gene, which reduces hypocretin secretion, is seen in
more than 85% of narcoleptics
4) REM Sleep Behavior Disorder
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(a) REM sleep behavior disorder is characterized by physical activity during REM
sleep and can lead to injury
(b) Often associated with a neurological disorder or a tumor
I. Sleep as a Form of Consciousness
1) Lucid dreamers are aware of when they are dreaming and in some cases can control
the nature of the dream
2) The gradations of sleep lead us to confront the question of what defines
consciousness
II. The Neural Bases of Consciousness
A. Awareness
1) Awareness of something is more specific than awareness and therefore easier to study
2) The question of how the brain combines information about an object is referred to as
the binding problem
3) Much of our behavior is guided by processes outside of awareness such as
proprioception
B. Attention
1) Attention refers to how the brain allocates its limited resources to focus on some
neural inputs while excluding others.
2) The Cheshire cat effect results from binocular rivalry
3) Attention is a physiological process, and changes in attention are matched with
changes in neural activity
4) The thalamus is a critical region but attention also requires working memory and
other brain areas
C. The Sense of Self
1) Body Image
(a) Body image is tied to a sense of self because we identify our body and its parts
(b) Phantom Limb (Chapter 11) illustrates how a loss of a body part is tied to a sense
of self
(c) Disruptions of body image diminish the sense of self
2) Memory
(a) A sense of self would likely be severely impaired by the loss of long term, but not
necessarily short term, memory.
(b) Confabulation suggests the importance of memory to self identity
D. Self, Theory of Mind, and Mirror Neurons
1) Sense of self requires an understanding of ourselves and the ability to distinguish
between self and others.
2) Mirror neurons may be necessary for understanding the intentions of others
E. Split Brains and Dissociative Identity Disorder: Disorders of Self
1) Surgical separation of the hemispheres gives us the opportunity to observe different
aspects of consciousness
2) The brain interpreter is hypothesized to be located in the left hemisphere an
integrate all cognitive processes going on within the brain
3) Dissociative Identity Disorder (DID) (formerly known as multiple personality
disorder) involves shifts in consciousness and behavior that seem to suggest distinct
personalities
(a) 90-95% of patients report childhood abuse
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(b) May be a mechanism to cope with significant and persistent emotional stress
(c) Incidence is increasing leading to doubt that all cases are “real”
(d) Amnesia associated with DID may be state-dependent learning
(e) MRI data suggest that the learning mechanisms may be involved
F. Theoretical Explanations of Consciousness
1) Most theories require a widely distributed neuronal network
2) Consciousness is sometimes theorized to be the coordination of this widespread
network
The thalamus is speculated to be the executive of consciousness
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