Biopsychology - Biological Rhythms Flashcards
Intro to biological rhythms
Repeated patterns of changes in the body
Regulated by an internal clock
3 types: circadian, ultradian and infradian
Circadian rhythms
Rhythms that last approx 24 hours
E.g. sleep-wake cycle
Controlled by endogenous pacemakers and exogenous zeitgebers
Endogenous pacemakers
Internal body clocks that regulate biological rhythms
Located inside our bodies
For sleep-wake cycle: suprachiasmatic nucleus (SCN)
In the hypothalamus above where the optic nerves cross
Controls release of melatonin from pineal gland
Exogenous zeitgebers
External cues that influence and reset our internal clocks
Most powerful for sleep-wake cycle: Light
Light detected by SCN even when eyes are closed
Adjusts internal clock to match external world
Chipmunk study
Compared chipmunks to those with damages SCN
Released into natural habitat and observed for 80 days
More chipmunks with damages SCN killed by predators
Importance of SCN in regulating sleep-wake cycle
Michel Siffre cave experiment
French researcher spent two months in underground caves in 1962
No exposure to natural light or clocks
Monitored sleep patterns and body activities
Maintained a regular sleep-wake cycle of about 25 hours
Lost track of time
Suggests existence of internal biological clock
Indicates natural cycle might be close to 25 hours without external cues
Czeisler’s Study Findings
● Controlled for artificial light
● Found natural circadian rhythm closer to 24.8 hours
● Much closer to 24 hours than previously thought
● Shows how artificial light can act as an exogenous
zeitgeber
● Importance of controlling variables in scientific research
Other Circadian Rhythms in the Body
● Body temperature fluctuations
● Digestive processes
● Hormone secretion patterns
● All affected by time of day
● Can you think of other bodily
Chronotherapeutics
● Study of how timing affects medical treatments
● Applies understanding of circadian rhythms to improve
healthcare
● Example: Timing of cancer treatments can affect
efficacy and side effects
● Potential to optimize medication schedules
Practical Applications
● Managing jet lag
● Shift work scheduling
● Optimizing study and work schedules
● Improving sleep hygiene
Circadian Rhythms and Mental Health
● Disrupted circadian rhythms linked to mental health issues
● Can affect mood disorders like depression and bipolar disorder
● Seasonal Affective Disorder (SAD) related to changes in light exposure
● Proper sleep hygiene important for mental well-being
Circadian Rhythms in Different Age Groups
● Circadian rhythms change throughout life
● Teenagers tend to have delayed sleep phase
● Older adults often experience earlier wake times
● These changes can affect school and work performance
Circadian Rhythms and Athletic Performance
● Athletic performance can vary based on time of day
● Some studies show peak performance in late afternoon
● Individual variations exist (“morning larks” vs “night
owls”)
● Could affect timing of training and competitions
Circadian Rhythms in a 24/7 Society
Modern society often ignores natural circadian rhythms
● 24/7 availability of artificial light and entertainment
● Potential health consequences of chronic circadian disruption
● Importance of “circadian hygiene” in digital age
Infradian Rhythms
● Last longer than 24 hours
● Can be weekly, monthly, or yearly
● Examples:
● Female menstrual cycle
● Seasonal Affective Disorder (SAD)
● Animal hibernation
Infradian Rhythm: Menstrual Cycle
● Monthly rhythm regulated by hormones
● Typical cycle: 28 days (can vary from 23-36 days)
● Ovulation occurs midway through cycle
● Estrogen levels highest during ovulation
● Progesterone increases after ovulation
Infradian Rhythm: Seasonal Affective Disorder (SAD)
● Yearly cycle related to seasons
● Typically causes depression in winter months
● Linked to melatonin secretion by the pineal gland
● Longer periods of darkness increase melatonin
production
External Influences on Infradian Rhythms
● Exogenous zeitgebers (external factors) play a significant role
● Light exposure can affect menstrual cycle length
● Pheromones may synchronize menstrual cycles among
women
Case Study: Cave Experiment
● Woman spent 3 months in a cave with minimal light
● Menstrual cycle shortened from 28 to 25.7 days
● Demonstrates the impact of light on infradian rhythms
Ultradian Rhythms
● Last less than 24 hours
● Occur multiple times per day
● Examples:
● Sleep cycles
● Eating patterns
Ultradian Rhythm: Sleep Cycles
● Complete cycle lasts about 90 minutes
● Alternates between REM and non-REM sleep
● Stages: Light sleep, Deep sleep, REM sleep
● Average person experiences 5 cycles per night
Stages of Sleep
● Stage 1-2: Light sleep (alpha and theta waves)
● Stage 3-4: Deep sleep (delta waves)
● Stage 5: REM sleep (similar to waking brain activity)
● Body paralyzed during REM to prevent acting out
dreams
Ultradian Rhythm: Eating Patterns
● Most humans eat about 3 meals per day
● Appetite rises and falls between meals
● Controlled by complex neural mechanisms
Flexibility of Ultradian Rhythms
● Case study: Randy Gardner stayed awake for 264 hours
● After extended wakefulness, body prioritized deep and REM sleep
● Demonstrates adaptability of sleep cycles
● What might be the long-term effects of disr
Individual Differences in Rhythms
● Research shows significant variations in sleep stage durations
● Particularly noticeable in deep sleep stages (3 and 4)
● Highlights importance of personalized approach in sleep research
Research Challenges
● Highly controlled environments may lack ecological validity
● Invasive monitoring can affect natural sleep patterns
● Balance needed between scientific rigor and real-world
applicability
