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Biological Rhythms and Sleep
®
AP Science Practice
Like the ocean, life has its rhythmic tides. Over varying time periods, our bodies fluctuate,
Research and with them, our minds. Let’s look more closely at two of those biological rhythms — our
These studies on circadian 24-hour biological clock and our 90-minute sleep cycle.
rhythms were correlational:
Researchers measured whether
participants were larks or owls, Circadian Rhythm
and then measured variables such
as creativity and punctuality. As 1.5-4 How do our biological rhythms influence our daily functioning?

1.5-4 How do our biological rhythms influence our daily functioning?

a result, they can’t conclude that
being a lark or an owl causes the
reported differences. Drawing The rhythm of the day parallels the rhythm of life — from our waking at a new day’s birth
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
causal inferences would require to our nightly return to what Shakespeare called “death’s counterfeit.” Our bodies roughly
random assignment. synchronize with the 24-hour cycle of day and night thanks to an internal biological clock
called the circadian rhythm (from the Latin circa, “about,” and diem, “day”). As morning

nears, body temperature rises; it then peaks during the day, dips for a time in the early after-
Copyright © Bedford, Freeman & Worth Publishers.
noon (when many people take siestas), and begins to drop again in the evening. Thinking
is sharpest and memory most accurate as we approach our daily peak in circadian arousal.
Have you ever pulled an all-nighter? You might remember feeling groggiest in the middle of
the night, but gaining a sense of new alertness with the arrival of your normal wake-up time.
Age and experience can alter our circadian rhythm. Most 20-year-olds are evening-
Eric Isselée/Shutterstock energized “owls,” with performance improving across the day (May & Hasher, 1998). Most
older adults experience more fragile sleep and are morning-loving “larks.” For our ances-
tors (and for today’s hunter-gatherers), a grandparent who awakened easily and early
helped protect the family from predators ( Samson et al., 2017 ). By mid-evening, when the
night has hardly begun for many young adults, retirement homes are typically quiet. After
about age 20 (slightly earlier for women), we gradually shift from being owls to being larks
( Roenneberg et al., 2004 ). Night owls tend to be smart and creative ( Giampietro & Cavallera,
2007 ). Morning types tend to do better in school, take more initiative, be more punctual, and
be less vulnerable to depression ( Preckel et al., 2013 ; Randler 2008 2009; Werner et al., 2015 ).
,
,
Sleep Stages eaming stages?

Peter Chadwick/Science Source Seeking sleep, we crawl into bed and fake it until we make it. Eventually, sleep overtakes
1.5-5 What is the biological rhythm of our sleeping and dreaming stages?

1.5-5
What is the biological rhythm of our sleeping and dr
us, and consciousness fades as different parts of our brain’s cortex stop communicating
(Massimini et al., 2005). Sleep may feel like time-traveling a few hours into the future. Yet
the sleeping brain remains active and has its own biological rhythm.
About every 90 minutes, you cycle through distinct sleep stages. This fact came to light
circadian [ser-KAY-dee-an] when 8-year-old Armond Aserinsky went to bed one night in 1952. His father, Eugene,
rhythm our biological clock; a University of Chicago graduate student, needed to test an electroencephalograph he had
regular bodily rhythms (for repaired that day (Aserinsky, 1988; Seligman & Yellen, 1987 ). Placing electrodes near Armond’s
example, of temperature and eyes to record the rolling eye movements then believed to occur during sleep, Aserinsky
wakefulness) that occur on a
24-hour cycle. watched the machine go wild, tracing deep zigzags on the graph paper. Could the machine
still be broken? As the night proceeded and the activity recurred, Aserinsky realized that the
REM sleep rapid eye
movement sleep; a recurring periods of fast, jerky eye movements were accompanied by energetic brain activity. Awakened
sleep stage during which vivid during one such episode, Armond reported having a dream, Aserinsky recalled 65 years later,
dreams commonly occur. Also of “a chicken walking through a barnyard” ( Nichols, 2018 ). Aserinsky had discovered what we
known as paradoxical sleep, now know as REM sleep ( r apid e ye m ovement sleep; sometimes called R sleep ).

because the muscles are relaxed Similar procedures used with thousands of volunteers showed the cycles were a normal
(except for minor twitches) but
other body systems are active. part of sleep ( Kleitman, 1960 ). To appreciate these studies, imagine yourself as a participant.
(Sometimes called R sleep. ) As the hour grows late, you feel sleepy and yawn in response to reduced brain metabo-
lism. (Yawning, which is also socially contagious, stretches your neck muscles and increases

94 Unit 1 Biological Bases of Behavior

03_myersAPpsychology4e_28116_ch01_002_163.indd 94 15/12/23 4:30 PM