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Chapter 5: Consciousness
Body Rhythms & Mental
• Awareness of oneself & the
• Fluctuations in subjective
experiences are accompanied by
predictable ups & downs in brain
activity & hormones
Biological Rhythms: The Tides of
• A biological clock in our brains governs the
waxing and waning of
–hormone levels,
–urine volume,
–blood pressure,
–and the responsiveness of brain cells to
• Many of these rhythms continue to
occur even in the absence of
external time cues; they are
endogenous, or generated from
• Circadian rhythm- occur
approximately every 24 hours
–Ex: sleep/wake cycle (best known)
–Ex: menstrual cycle
• Influence everything from the
effectiveness of medicines taken at a
certain time to alertness &
performance on the job
Circadian Rhythms
• Exists in plants, animals, insects, &
• Reflect the evolutionary adaptation
of organisms to the many changes
associated with the rotation of the
• To study, volunteers must be
isolated from sunlight, clocks, &
all clues to time
The Body’s Clock
• Circadian rhythms are controlled by a
biological clock, or overall
• Controlled by a tiny tear drop shaped
cluster of cells in the hypothalamus
called the suprachiasmatic nucleus
• Neural pathways from special
receptors in the back of the eye
transmit into the SCN & allow it to
respond to changes in light & dark
• SCN sends out messages to respond
to these changes
• Other clocks also exist and some may
operate independently of the SCN.
• For most circadian rhythms, the SCN
is regarded as the master pacemaker.
When the Clock Is Out of Sync
• Under normal conditions, the
rhythms are synchronized, just as
wristwatches can be
• Their peaks may occur at different
times, but they occur in phase with
one another.
• If you know when one rhythm peaks,
you can predict when another will do
When the Clock Is Out of Sync
• When your normal routine changes, your
circadian rhythms may be thrown out of
phase with one another.
–Internal desynchronization- “Jet lag”,
shift work
• Sleep & wake patterns usually adjust
quickly, but temperature and hormone
cycles can take several days to return to
–Can be affected by illness, stress,
fatigue, excitement, exercise, drugs,
meal times, etc.
–Differ greatly among individuals
because of genetics
Moods and Long-term Rhythms
• In humans, long-term cycles have been
observed in everything from the
threshold for tooth pain to conception
• Folklore holds that our moods follow
similar rhythms, particularly in response
to seasonal & menstrual changes.
• But do they?
Does the Season Affect Moods?
• Clinicians report that some people
become depressed every winter,
when periods of daylight are short,
and improve in mood each spring, as
daylight increases
• This pattern that has come to be known
as seasonal affective disorder (SAD)
–feelings of sadness, lethargy, &
• Treated with phototherapy
–No conclusive evidence
Does the Menstrual Cycle Affect Moods?
• Controversy has
raged about
another longterm rhythm,
the monthly
menstrual cycle.
• Are these physical changes correlated
with emotional or intellectual
–Evidence shows physical changes
–Emotional symptoms are rare
Does Testosterone Affect Moods
• The notion that hormones affect mood
& performance has rarely been
extended to men.
• Men’s hormones also fluctuate in a
cyclical manner.
• There may be a bias to attribute
women’s moods to hormones, but not
• High levels have been linked to
criminal violence, delinquency,
rambunctiousness, sociability,
restlessness, elation, sadness,
moodiness, aloofness, & being a trial
–Behavior affects testosterone levels
as well as the reverse