Psyc 388 Midterm PDF

Module 3: Evolution and Adaptive Significance of Circadian Clocks Main Concepts: − Phylogenetic Ubiquity of Clocks: Circadian clocks are found in all domains of life and likely evolved very early. − Evolutionary Hypotheses for Clock Development: o External Coordination Hypothesis:...

Module 3: Evolution and Adaptive Significance of Circadian Clocks Main Concepts: − Phylogenetic Ubiquity of Clocks: Circadian clocks are found in all domains of life and likely evolved very early. − Evolutionary Hypotheses for Clock Development: o External Coordination Hypothesis: ▪ Escape from light (protection from damaging UV radiation). ▪ Escape from oxygen radicals (produced by photosynthesis). o Internal Coordination Hypothesis: ▪ Separation of incompatible processes (e.g., nitrogen fixation and photosynthesis). ▪ Sequencing of related processes (e.g., glucose storage and release). − Why Clocks Remain: Clocks help organisms anticipate environmental changes, optimize biochemical processes, and improve survival and reproductive fitness. − Species-Specific Clock Functions: o Foraging: Some animals, like bees, have "zeitgedachtnis" (time-sense) for food availability. o Navigation: Using circadian clocks for time-compensated sun compass orientation. o Photoperiodism: Clocks help measure day length and regulate seasonal behaviors. o Physiological Advantages: Clock disruption in mammals can lead to health issues like metabolic disorders and cancer, showing clocks’ importance for survival. Additional Concepts from Week 2 Slides: − Adaptive Significance of Circadian Clocks: Circadian clocks provide evolutionary advantages by enabling organisms to anticipate regular environmental changes, thus enhancing their ability to forage, reproduce, and avoid predators.  − Circadian Clocks and Survival: Circadian rhythms are beneficial but not strictly necessary for survival in all species. However, disruption of circadian rhythms can lead to health problems in humans and other mammals. Module 4: Principles of Entrainment Main Concepts: − Circadian Rhythms: These rhythms are self-sustaining, temperature- compensated, and entrainable with ~24-hour periods. − Entrainment: Synchronizing the circadian rhythm to environmental (typically light- dark) cycles. ▪ Key Processes in Entrainment: ▪ Phase Shifts and Phase Response Curves (PRC): Light at different times during the circadian cycle causes phase shifts in rhythms. ▪ The Role of Light as a Zeitgeber (Time-Giver): Light is the main cue synchronizing rhythms to local time. − Masking vs. Entrainment: ▪ Masking: Direct effects of light on behavior (like suppressing activity) without affecting the underlying circadian clock. ▪ Entrainment: A true clock-mediated adjustment to light-dark cycles. − Non-Parametric Entrainment: Daily phase shifts ensure the clock remains synchronized without altering the period. − Real-World Application: Understanding entrainment can help manage circadian disorders, shift work, and jet lag. Module 5: Non-Photic Entrainment Stimuli Main Concepts: − Non-Photic Zeitgebers: Stimuli other than light that can affect the circadian clock, such as: o Social Interactions o Exercise and Behavioral Arousal o Food and Feeding Times o Temperature − Examples of Non-Photic Effects:  o Social Entrainment: Social cues, such as maternal nursing in rabbits or synchronization of rhythms within animal groups (e.g., beavers, bats), can influence circadian rhythms. o Exercise: Physical activity can shift circadian rhythms, with wheel running in rodents advancing or delaying their clocks. o Food Intake: Feeding times can also entrain circadian rhythms, particularly in neonates or animals with food-dependent cycles. − Interactions Between Photic and Non-Photic Stimuli: Non-photic cues can interact with light exposure to modulate circadian rhythms in animals and humans, which may affect human health, especially in shift workers. Module 6: Entrainment by Meal Timing − What is Meal Timing Entrainment? o Meal timing entrainment refers to the synchronization of circadian rhythms to the timing of food intake rather than light cues. This type of entrainment is particularly relevant in cases where organisms are exposed to constant lighting conditions (e.g., constant dark or light) or when the light-dark cycle is weak. − How Does Meal Timing Entrain Circadian Rhythms? o The circadian clock can be entrained not only by light but also by food availability. When food is consistently available at specific times of day, it can reset certain oscillators in the body, especially those related to metabolism and digestion. o Food-entrainable oscillators (FEOs) exist in peripheral tissues like the liver, which respond strongly to feeding times and regulate metabolic cycles independently of the central clock located in the suprachiasmatic nucleus (SCN). − Mechanisms of Meal Timing Entrainment o Peripheral Clocks: Meal timing primarily affects peripheral circadian clocks (e.g., in the liver, pancreas, and gut) more than the central clock (SCN). The liver's clock, for instance, is sensitive to the timing of food intake and regulates metabolism in anticipation of regular feeding times.  o Hormonal Responses: Hormones like insulin, glucagon, and ghrelin are influenced by meal timing and play a role in resetting peripheral clocks. − Evidence for Meal Timing as a Zeitgeber o Rodent Studies: In rodents, restricting food availability to certain periods of the day causes their circadian activity to shift, even in constant darkness or light. These studies suggest that food can be a potent zeitgeber (time cue) that influences circadian rhythms. o Food Anticipatory Activity (FAA): Animals exhibit food anticipatory activity when they are about to receive food at a predictable time. This behavior suggests that circadian rhythms in the body prepare for meals by aligning metabolism, body temperature, and other functions. − Interaction Between Light and Meal Timing o Light and meal timing can act together or independently to entrain circadian rhythms: o Light cues typically synchronize the central SCN clock, while meal timing can entrain peripheral clocks. o When the central and peripheral clocks become misaligned (e.g., in shift workers), the mismatch can lead to metabolic problems like obesity and diabetes. − Implications of Meal Timing for Human Health o Metabolic Health: Irregular meal times or eating late at night can disrupt the natural rhythms of peripheral clocks, leading to metabolic issues like obesity, insulin resistance, and impaired glucose tolerance. o Shift Work and Jet Lag: Meal timing is especially important in shift workers, as eating meals at inappropriate times (relative to the body's circadian phase) can exacerbate circadian misalignment. For people suffering from jet lag or working irregular hours, adjusting meal timing may help reduce the adverse effects of circadian disruption. − How Meal Timing Differs From Light Entrainment  o While light entrainment primarily affects the SCN, meal timing entrainment has its strongest effects on peripheral oscillators. o Unlike light, which directly suppresses melatonin and shifts sleep-wake cycles, meal timing works through metabolic and hormonal pathways that influence body temperature, insulin sensitivity, and fat storage. − Practical Applications of Meal Timing o Time-Restricted Feeding (TRF): Studies show that restricting food intake to specific time windows (e.g., eating within an 8-12 hour window) can have significant benefits for metabolic health, even when caloric intake remains the same. o Fasting and Rhythms: Fasting or intermittent fasting, where meals are skipped or delayed, can also entrain circadian rhythms, potentially improving metabolic outcomes by aligning the body's rhythms with feeding and fasting cycles. − Current Research in Meal Timing Entrainment o Chrononutrition: This field studies the effects of meal timing on health and circadian biology, with growing evidence that aligning meals with circadian rhythms can improve health outcomes. o Human Studies: While animal studies provide strong evidence for meal timing as a zeitgeber, human studies are still exploring the best practices for meal timing, especially in conditions like shift work or irregular schedules. Main points: − Meal timing is a potent, non-photic zeitgeber that primarily influences peripheral clocks in the body. − Food-entrainable oscillators (FEOs) in tissues like the liver are sensitive to the timing of food intake and regulate metabolism accordingly. − Meal timing entrainment is important for maintaining metabolic health and mitigating the effects of circadian disruption, particularly in shift workers or those experiencing jet lag. − Food anticipation is a behavioral marker of circadian rhythms entrained by feeding schedules. Module 7.1: Photic and Non-Photic Entrainment in Humans Main Concepts: − Photic Entrainment: In humans, light is the most powerful zeitgeber and can shift circadian rhythms based on intensity, duration, and timing. o Phase Response Curves (PRCs): These curves represent how different intensities and times of light exposure influence circadian shifts in humans. o Melatonin Suppression: Light exposure suppresses melatonin, a hormone critical for sleep-wake regulation. − Non-Photic Stimuli in Humans: o Social Cues: Although these have weaker effects in humans than in animals, co-habitation and social interactions can influence circadian rhythms. o Exercise: Physical activity, especially at night or early morning, can shift the circadian clock and aid in re-entrainment after time-zone changes. o Feeding: There is limited data, but meal timing could influence human circadian rhythms, especially during shift work or jet lag. − Circadian Blindness: Some blind individuals lack photic input to the circadian clock, leading to free-running rhythms that don’t synchronize with the environment. Treatments like melatonin and strict sleep schedules can help in such cases. Study Questions 1. What are the primary theories as to why circadian clocks first evolved? ▪ External Coordination Hypothesis: o Escape from light: Protect early organisms from UV radiation by restricting replication to the night. o Escape from oxygen radicals: Protection from oxygen radicals produced by photosynthesis by confining antioxidant production to night. ▪ Internal Coordination Hypothesis: o Separation of incompatible processes like nitrogen fixation and photosynthesis (spatial/temporal). o Sequencing of processes, ensuring biochemical reactions occur in the correct order. 2. Are circadian rhythms found in all kingdoms of life? Yes, circadian rhythms are found in all three domains and six kingdoms of life (Animalia, Plantae, Fungi, Protista, Bacteria, Archaea). 3. What do we mean by a ‘continuously consulted clock’? A continuously consulted clock is a circadian oscillator that provides a constant reference for recognizing different phases of the day, allowing organisms to adjust behaviors accordingly. 4. What is ‘Zeitgedachtnis’? Zeitgedachtnis is the time-sense memory of animals, allowing them to remember the time of day when food or other important resources are available. 5. What is an interval timer and how do we decide if a rhythm is controlled by an entrained oscillator or an interval timer? An interval timer is like an hourglass, measuring the time between two events. If a rhythm persists under constant conditions (like light or dark), it is controlled by an entrained oscillator rather than an interval timer. 6. Define homeostasis. Homeostasis is the maintenance of stable internal physiological conditions, such as temperature and pH, in response to changing external conditions. 7. Are circadian clocks physiologically advantageous? Yes, circadian clocks provide advantages by coordinating internal processes and helping organisms anticipate regular environmental changes. 8. Are circadian clocks indispensable for life? Not necessarily. Some organisms (like troglobytic species or reindeer in the high Arctic) lack rhythms under specific conditions, but circadian rhythms confer evolutionary advantages in many environments. 9. How do honey bees communicate the location of food sources to other bees? Honey bees use the waggle dance, which conveys both direction and distance to food sources in relation to the sun’s position. 10. What is eclosion, and when do fruit flies do this? Eclosion is the emergence of adult flies from their pupal cases. Fruit flies typically eclose at dawn to optimize conditions for survival. 11. Can losing your circadian clock make you more vulnerable to predation in the wild? Who was the first person to test this, and what was the experiment? Yes, DeCoursey tested this by SCN-lesioning chipmunks. Those without circadian clocks exhibited nighttime restlessness and were more vulnerable to predation. ▪ SCN-lesioning refers to a procedure where the suprachiasmatic nucleus (SCN), the central circadian clock in the brain, is deliberately damaged or removed in order to study its function. The SCN is located in the hypothalamus and is responsible for regulating the body's circadian rhythms, including the sleep-wake cycle, hormone release, and other daily physiological processes. ▪ By lesioning (destroying) the SCN in animals, researchers can observe how the absence of the central circadian clock affects behavior, physiology, and the ability to maintain regular rhythms. This method is used to: o Investigate the role of the SCN in controlling circadian rhythms. o Determine whether other parts of the body (peripheral clocks) can compensate for the loss of the SCN. o Study how behaviors like sleep, feeding, and activity become disrupted without the SCN’s influence. 12. What might be the purpose of circadian rhythms in blind mole rats that live underground? Even without light cues, blind mole rats may use circadian rhythms for internal processes like metabolism, temperature regulation, and social interactions. 13. What is meant by "Swamping" as a survival strategy and what has this got to do with circadian clocks? Swamping refers to synchronizing reproductive events (e.g., spawning) to overwhelm predators. Circadian clocks help organisms time these events precisely. 14. What are the ‘subjective day’ and ‘subjective night’? The subjective day is when an organism perceives it as day based on its internal clock, even in constant conditions. Subjective night is similarly defined for the night phase. 15. What is the ‘non-parametric’ model of entrainment, and what does it predict? The non-parametric model suggests entrainment occurs through discrete phase shifts (advances or delays) based on light exposure at specific times. It predicts gradual re-entrainment to time zone shifts. 16. What is ‘parametric’ entrainment? Parametric entrainment occurs when continuous exposure to light modulates the clock's period, ensuring stability in rhythmic behavior. 17. What is a phase shift? What is a ‘delay’ and what is an ‘advance’? A phase shift is a change in the timing of a circadian rhythm. A delay means the rhythm occurs later, while an advance means it occurs earlier. 18. What is a ‘phase response curve’? What kind of data are plotted on a PRC? How does the PRC explain entrainment? A PRC plots phase shifts (advances/delays) against circadian time at which light was given. It explains how different light exposures shift rhythms, helping the clock align with the environment. 19. What direction of phase shift is needed for a person from Vancouver to entrain to local time after flying east or west across several time zones? Flying east requires a phase advance (shift the clock forward), and flying west requires a phase delay (shift the clock backward). 20. How long is one circadian hour? How is it calculated? One circadian hour is 1/24th of the organism’s circadian period, which might be slightly longer or shorter than 24 hours. 21. How much light does a flying squirrel need to see to entrain to an LD cycle? Flying squirrels can entrain to even brief exposures to light, such as 1-2 minutes of light per day. 22. What kind of phase shift is induced in nocturnal animals by light exposure during the day? Early night? Late night? ▪ Daytime light exposure: Usually no effect or a delay. ▪ Early night: A delay in the circadian rhythm. ▪ Late night: An advance in the rhythm. 23. What kind of phase shift is induced in Syrian hamsters by a 3h bout of exercise (wheel running)? ▪ Day/Rest phase: Typically, no phase shift. ▪ Early night: Phase delay. ▪ Late night: Phase advance. 24. What kind of phase shift is needed to entrain to a 24h LD cycle if the circadian clock has an intrinsic periodicity of 24.5 h? A phase advance is needed to reduce the rhythm from 24.5h to 24h. 25. Can circadian rhythms be entrained or shifted by stimuli other than light? Yes, stimuli like exercise, feeding, social interactions, and temperature can shift rhythms (non- photic entrainment). 26. Describe evidence for ‘nonphotic’ entrainment in bats, beavers, and rabbits. ▪ Bats: Roosting bats can entrain to social stimuli like the activity of conspecifics. ▪ Beavers: Families in lodges synchronize their rhythms in the absence of light. ▪ Rabbits: Neonates entrain to maternal feeding times. 27. Can circadian rhythms in hamsters be phase-shifted by being woken up in their usual rest phase for a few hours? Is any method of keeping the hamsters awake effective? Yes, but only certain arousal methods (like forced running) are effective in inducing phase shifts. 28. In Syrian hamsters, can scheduled exercise alter entrainment to LD cycles? Yes, scheduled exercise can facilitate entrainment and shift rhythms. 29. Does the amount that a rat runs in its wheel in constant dark have an effect on free-running rhythms? Yes, the more the rat runs, the shorter its circadian period becomes. 30. Are there species differences in the response of circadian rhythms to exercise? Yes, hamsters show larger phase shifts to exercise than rats or mice. 31. In what ways do the phase response curves to light pulses and exercise differ, if at all? The PRC to light shows larger shifts, while the PRC to exercise has smaller shifts and is dependent on the time of day. 32. Are photic and non-photic PRCs exact mirror images? No, they are not exact mirror images; they have different shapes and magnitudes of shifts. 33. Can daily feeding schedules entrain free-running rhythms in the constant dark? Are there species differences in the likelihood of this occurring? Yes, feeding schedules can entrain rhythms, especially in rodents. Species differences exist, with some more reliant on food for entrainment than others. 34. What is a ‘temporal niche switch’? Under what conditions has it been shown to occur in nocturnal rodents? A temporal niche switch is when animals change from being nocturnal to diurnal (or vice versa), often due to environmental pressures. 35. Can a single day of food deprivation cause phase shifts of free-running rhythms in Syrian hamsters? If so, what is the likely cause of the shifts? Yes, food deprivation can cause phase shifts, likely due to the stress or arousal it induces. 36. What is the evidence that anticipation of a daily meal is controlled by food-entrained circadian oscillators? What is the evidence that there is likely more than one food-entrainable oscillator? Activity rhythms before feeding time show anticipation. The persistence of food-anticipatory rhythms even when the master clock (SCN) is lesioned suggests multiple oscillators. 37. What is masking, and how is it different from entrainment? Masking is a direct effect of stimuli (like light) on behavior that does not involve the circadian clock. Entrainment adjusts the internal clock. 38. Can circadian rhythms in humans entrain to light-dark cycles? Early studies by Aschoff and Wever suggested maybe no, while a later study by Czeisler indicated yes. What was the critical difference between the Czeisler study and the earlier work? Czeisler's study used strict light control with no dim light allowed, which showed humans can entrain, unlike Aschoff's study, which allowed self-selected light exposure. 39. Does exercise shift circadian rhythms in humans, and if so, how does the PRC compare to the PRC to light? Yes, exercise shifts circadian rhythms. However, the PRC to exercise has smaller shifts than the PRC to light. 40. Which circadian rhythm is thought to provide the most accurate measure of the phase of the circadian clock in humans? The melatonin rhythm, particularly the melatonin onset, is considered the most accurate measure. 41. When other factors are controlled, is scheduled bedtime a Zeitgeber in humans? Scheduled bedtime is a weak zeitgeber compared to light or food. 42. Describe the ‘constant routine’ procedure for measuring circadian rhythms and phase shifts in humans. The constant routine involves keeping subjects in constant conditions (dim light, constant temperature) while measuring biological rhythms like melatonin or core body temperature. 43. What do we mean by ‘circadian blind,’ and how can this be diagnosed? Circadian blindness occurs when a person’s clock doesn’t respond to light. It can be diagnosed by testing for melatonin suppression in response to light. 44. Can some blind people entrain to 24h LD cycles? Yes, some blind people can still entrain if their circadian system can perceive light through non- visual pathways. 45. What determines how long it takes to entrain to a new time zone? Factors include the magnitude and direction of the time shift, individual circadian period, and exposure to light at the correct phase.