1. Biological Rhythms
A periodic, more or less regular fluctuation in a biological system.
They may or may not have psychological implications.

2. Biological Rhythms
Our biological clocks are the internal chemical units that control parts of the body all by themselves and are programmed and regulated by nature.
A biological clock in our brains (a teardrop shaped cluster of cells in the hypothalamus) regulates the increase and decrease of hormone levels, urine volume, blood pressure, and the responsiveness of brain cells to stimulation
It is endogenous
Generated from within
Occurs absent of time cues
Tiny teardrop shaped cluster of cells in the hypothalamus
For more information on biological clocks, see

3. Endogenous Biological Rhythms
Circannual Rhythms
Occurs generally about once a year
Example: seasonal variations (bears hibernating, birds migrating, seasonal affective disorder)
Circadian Rhythms
Occurs about every 24 hours
Example: the sleep-wake cycle
Infradian Rhythms
Occurs less frequently than once a day
Example: the 28 day menstrual cycle
Ultradian Rhythms
Occurs more frequently than once a day
Example: stomach contractions, hormone fluctuations, 90 minute sleep cycles

4. More on Circadian Rhythms
The sequences of behavioral changes that occur every 24 hours. Circa means “about” and dian means “a day,” so circadian means “about a day.”
Humans and other animals operate on a 24-hour biological cycle. These daily cycles are particularly important in the regulation of sleep, but also in the regulation of temperature, blood production, hormone production, and other bodily processes.
For example, in our 24-hour cycle we usually experience high and low points. For most of us, the low point (low temperature, low blood pressure, weakness, etc.) occurs between 3 a.m. and 5 a.m.
Circadian rhythms vary from person to person, and different people may have different optimal times to fall asleep (Are you a lark or an owl? Take the survey to find out!), have a good night’s sleep, etc.
It is best to take a test or study during your circadian peaks!

5. What is your natural rhythm?
Take the automated “Morningness-Eveningness Questionnaire” and receive personalized feedback about the peak time of day for you to engage in certain tasks. You will learn when your melatonin levels begin to rise and when your "natural bedtime“ is, among other things:

6. The Body’s Clock
Special receptors in the eye and the hypothalamus gland allow the body to respond to changes in light and dark
Ex: melatonin goes up in dark and down in light
Melatonin is used to treat insomnia and blind people with sleep-wake problems

7. Biological Rhythms and Sleep
Physiological pathway of the biological clock:
The pathway for regulation of the human biological clock appears to be based in light levels, which go from the eye to an area of the brain called the suprachiasmatic nucleus (in the hypothalamus). This nucleus tells the pineal gland to secrete melatonin, a hormone that adjusts biological clocks.
Light levels  retina  suprachiasmatic nucleus of hypothalamus  pineal gland  secretion of melatonin
Melatonin supplements are sold in the U.S. as nutritional supplements, but many researchers worry that people are taking too high doses of this substance (the most people should take in a day is 1 mg, but most pills come as 2 or more mg), when long-term effects have not been tested. Melatonin is a regulated drug in Canada, Great Britain, and many other countries. Research shows that may be helpful in the treatment of jet lag, but timing is very important and hard to get right. Studies also show that melatonin may be useful as a mild sedative, more so in the daytime than at night, when melatonin levels are naturally higher.
Humans and other animals operate on a 24-hour biological cycle. These daily cycles are particularly important in the regulation of sleep, but also in the regulation of temperature, blood production, hormone production, and other bodily processes.
Circadian rhythms vary from person to person, and different people may have different optimal times to fall asleep, have a good night’s sleep, etc.
The pathway for regulation of the human biological clock appears to be based in light levels, which go from the eye to an area of the brain called the suprachiasmatic nucleus (in the hypothalamus). This nucleus tells the pineal gland to secrete melatonin, a hormone that adjusts biological clocks.
Melatonin supplements are sold in the U.S. as nutritional supplements, but many researchers worry that people are taking too high doses of this substance, when long-term effects have not been tested. Melatonin is a regulated drug in Canada, Great Britain, and many other countries. Research shows that may be helpful in the treatment of jet lag, but timing is very important and hard to get right. Studies also show that melatonin may be useful as a mild sedative, more so in the daytime than at night, when melatonin levels are naturally higher.

8. Biological Rhythms and Sleep
Circadian Rhythms occur on a 24-hour cycle and include sleep and wakefulness. Termed our “biological clock,” it can be altered by artificial light.
Preview Question 3: How do our biological rhythms influence our daily functioning and our sleep and dreams?
Light triggers the suprachiasmatic nucleus to decrease
(morning) melatonin from the pineal gland
and increase (evening) it at nightfall.

9. Entrainment
Biological rhythms are synchronized with external events such as changes in clock time, temperature, and daylight.
Most societies are influenced by time cues & people’s bodies become synchronized to those time cues
Entrainment is the process of altering the free-running cycle (training it) to fit a different rhythm.
For example, the sleep-wake cycle can be changed. This cycle is free-running at birth (think about babies who wake up every few hours to eat), but after a few months parents have normally trained the babies to fit the adult’s schedule. The same thing happens with students over summer break. You get used to a different sleep-wake cycle, and you must train your body (entrainment) to a new cycle when school starts.

10. Internal Desynchronization
A state when biological rhythms are not in phase with each other (when the clock is out of sync)
When one changes, others are thrown off
Why would a rhythm change? Changes in routine.
Airplane flights- Jet lag can affect energy level, mental skills, & motor coordination
Adjusting to a new work shift or working swing shifts- efficiency drops, tired, irritable, more accidents, sleep disturbances, digestive disorders
Circadian rhythms also affected by genetics, illness, fatigue, stress, etc.
Some people are night owls, some are early birds

11. Figure 5.3: Effects of direction traveled on the performance of professional baseball teams.
To gain some insight into the determinants of jet lag, Recht, Lew, and Schwartz (1995) analyzed the performance of visiting teams in major league baseball over a three-year period. In baseball, visiting teams usually play 3–4 games in each destination city, so there are plenty of games in which the visiting team has not traveled the day before. These games, which served as a baseline for comparison, were won by the visiting team 46% of the time. Consistent with the observation that flying west creates less jet lag than flying east, visiting teams that flew westward the day (or night) before performed only slightly worse, winning 44% of the time. In contrast, visiting teams that flew eastward the day before won only 37% of their games, presumably because flying east and shortening one’s day creates greater jet lag. Source: Adapted from Kalat, J. W. (2001). Biological psychology. Belmont, CA: Wadsworth.
Figure 5.3: Effects of direction traveled on the performance of professional baseball teams.
To gain some insight into the determinants of jet lag, Recht, Lew, and Schwartz (1995) analyzed the performance of visiting teams in major league baseball over a three-year period. In baseball, visiting teams usually play 3–4 games in each destination city, so there are plenty of games in which the visiting team has not traveled the day before. These games, which served as a baseline for comparison, were won by the visiting team 46% of the time. Consistent with the observation that flying west creates less jet lag than flying east, visiting teams that flew westward the day (or night) before performed only slightly worse, winning 44% of the time. In contrast, visiting teams that flew eastward the day before won only 37% of their games, presumably because flying east and shortening one’s day creates greater jet lag. Source: Adapted from Kalat, J. W. (2001). Biological psychology. Belmont, CA: Wadsworth. Reprinted by permission.

12. The Debate
Are our rhythms endogenous or are they environmentally determined?
How do we find out?
To study endogenous circadian rhythms, scientists isolate volunteers from time cues.
Experiments without sunlight or clocks
Will the “day” be longer than 24 hours or less?

13. The Experiment Stefania Follini
Spent 4 months (130 days) in an underground cave in New Mexico without any clocks or sunlight
Inside her twenty by twelve foot acrylic glass room, away from all cues to the normal 24-hour daily cycle, her biological clock drifted away from its regular rhythm.
Spent hours awake
10 hours asleep
With her slowed-down daily cycle, her meals were more spread out and she lost weight. She reported that at one point her menstrual cycle had stopped.
When asked, thought she had only been in the cave for 2 months

14. Moods and Long-Term Rhythms
Seasonal Affective Disorder
and PMS

15. Moods & Long-Term Rhythms
Do moods respond to …
Seasonal changes?
In women, menstrual changes?

16. Seasonal Affective Disorder
A controversial disorder in which a person experiences depression during the winter and an improvement of mood in the spring.
Winter months = sadness, lethargy, and drowsiness
Affects 1% of Americans
Treatment involves phototherapy or exposure to fluorescent light (
Evaluating frequency of and treatment for S.A.D. is difficult
Most people claiming S.A.D. just don’t like the winter
Sleet, snow, cold
Less active
Lonely during the holidays
See CNN article on S.A.D:

17. Menstrual Cycles and Mood
Does the menstrual cycle affect mood?
Women do have physical symptoms
Cramps, breast tenderness, and water retention
Can make women grumpy just like pain can make men grumpy
Emotional symptoms are rare
Irritability and depression – fewer than 5% of women have symptoms predictably.

18. Studies done comparing mood swings and menstrual cycles
Women were polled about their psychological & physical well-being without revealing the true purpose of the study (women kept daily records for 2 or 3 months)

19. The Findings No gender differences exist in mood
Same emotional symptoms & number of mood swings in a month
No relation exists between stage of the menstrual cycle & emotional symptoms
Even when women firmly believe they do
No consistent PMS pattern across menstrual cycles
No connection exist between PMS and behavior
Work performance, motor skills, problem solving, etc

20. Why Women Overestimate “PMS”
Why do so many women think they suffer from emotional symptoms?
They notice depression or irritability when these moods occur premenstrually but overlook times when moods are absent premenstrually
Symptoms are excused as “caused by stress” when they occur at other times
They are influenced by cultural attitudes and myths about menstruation
The notion that hormones impair mood & performance is rarely extended to men (testosterone levels rise & fall in a cyclical manner also)

21. Figure 7.2 Menstruation, actual mood, and perceived mood Myers: Psychology, Eighth Edition Copyright © 2007 by Worth Publishers