MODULE 4- PSYC 388 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED

MODULE 4- PSYC 388 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED Terminology: -oscillator: -pacemaker: Use orchestra as a metaphor, - is an oscillator incapable of keeping a rhythm? - what r Local oscillators? - Removal of a local oscillator ? - how many pacemakers do we have? - circadian timekeeping system in multicellular organisms contains many oscillators, playing different roles, in a hierarchy. - Oscillator: as any device that produces a rhythm. - pacemaker: 'master oscillator' that controls the timing of other oscillators or directly driven processes. - An oscillator might be incapable of keeping a rhythm on its own, and may be completely dependent on signals from the pacemaker. We might be inclined to call this a 'directly driven process', and not a true oscillator at all. Alternatively, we might call this a 'slave oscillator'. Without the pacemaker, the slave oscillator stops. Oscillators can be 'masters', or 'slaves', or they can be something in-between. We can call these 'secondary' or 'local' oscillators. - Local oscillators would be those found in a specific body tissue or organ or brain region, which are responsible for inducing circadian rhythms in the functions of that particular tissue, organ or brain region. Removal of a local oscillator would affect rhythmicity in the affected tissue, and may have no effect on rhythms elsewhere in the organism. - Removal of a pacemaker, by contrast, would affect rhythms throughout the organism. In the absence of a pacemaker, local oscillators may continue to oscillate, but would eventually become desynchronized from other local oscillators, resulting in loss of circadian rhythmicity at the level of the whole tissue or organ. - Circadian pacemakers follow the cycles of nature, most importantly the rising and setting of the sun. There could be multiple pacemakers, with one responding to light, and others responding to nonphotic stimuli such as temperature or food. Oscillator can serve as a clock: In everyday life, we speak of clocks and watches, not of oscillators and pacemakers. When an oscillator (or pacemaker) is synchronized to the external world, a specific phase of the oscillator (the current position of the oscillator or pacemaker within its cycle) corresponds to a particular time of day in the local environment. If the phase of the oscillator represents a time of day, then the oscillator can serve as a clock. This definition aligns with our everyday notion of a clock. It is a device that allows us to know the time of day, even if we cannot see whether the sun is up, or where it is in the sky. There are other types of timing devices: give eg 'interval timer'? is it an oscillator? eg of one? egs of interval timer? There are other types of timing devices: 1. 'interval timer', which can time one cycle, but then stops and needs to be reset. It is not an oscillator. Hourglass clocks are an example of an interval timer; an hourglass clock has two compartments connected by a narrow neck. The hourglass clock is built such that one compartment can be filled with an amount of sand that takes an hour (or some other duration) to completely empty into the other compartment under the force of gravity can measure an hour (or some other interval). We call this a 'clock', but it is limited to timing one set interval, and does not provide information about time of day. Stopwatches are another example of an interval timer. Stopwatches can be distinguished from hourglass clocks because they are flexible, that is, they can be used to measure any interval. Turning an oscillator into a clock: Circadian clocks have three defining characteristics? Circadian clocks have three defining characteristics. 1. They are self-sustaining and persist with an ~ 24h periodicity in constant conditions 2. They are temperature compensated 3. They are entrainable by environmental stimuli Turning an oscillator into a clock: give eg of different roles of Circadian clocks?alarm clocks, wristwatches & measure day length? To accomplish these functions, the circadian clock must have astable 'phase relationship' with what? entrainment? - circadian clocks coordinate behaviour and physiology with predictable daily events in the real world. - Circadian clocks can act like alarm clocks, and trigger behavioural or physiological events at appropriate times of day. - Circadian clocks act as wristwatches (also called 'continuously consulted clocks'), enabling animals to recognize and remember multiple times of day at which important things (like food) are encountered. The circadian wristwatch enables some animals to use the sun as a landmark for travel (time-compensated sun compass orientation). - Circadian clocks are also used to measure day length (photoperiodism) and thereby permit some species to organize their behaviour and physiology into annual rhythms. - It is self-evident that to accomplish these functions, the circadian clock must have astable 'phase relationship' with the solar day. If the circadian clock is not synchronized to the LD cycle, then its phase will not be predictive of local environmental time, and outside of controlled environments (e.g., a zoo, household or laboratory) it may be worse than useless. It would cause animals to wake up and go to sleep at the wrong time of day for finding food and mates and staying safe. - Synchrony is critical. The mechanism by which synchrony is achieved is called entrainment. entrainment: The mechanism by which synchrony is achieved is called entrainment. Turning an oscillator into a clock: Entrainment must solve two problems: what is the objective of entrainment? 1. First, circadian clocks cycle with a periodicity that only approximates the 24h day. The process of entrainment must somehow adjust the clock on a regular basis so that it does not drift out of synchrony with the outside world (as it does when organisms are kept in constant light or dark). 2. Second, the process of entrainment must somehow ensure that organisms do the right thing at the right time of day. In strictly diurnal animals, vision is usually the dominant sense, and night vision is weak. To be useful, the circadian clock must be synchronized to the outside world such that sleep and waking states occur at the appropriate time of day. - objective of entrainment is to control both the period and the phase of the circadian clock, to align it stably with the environment. Any external stimulus that can entrain a circadian clock is called a Zeitgeber (German for 'time- giver'). Zeitgeber Any external stimulus that can entrain a circadian clock. Masking: diurnal animals and nocturnal rodents eg? 'negative masking' 'positive masking - Masking refers to a direct effect of an environmental stimulus on behavioural state. Light and dark can directly affect behaviour. - In diurnal animals, light tends to stimulate (or at least permit) activity and increase alertness, while in nocturnal animals, light inhibits activity and promotes sleep. - Among chronobiologists, the direct effect of light on behaviour is called masking because light can 'mask' the true phase of the circadian clock. - Nocturnal rodents are normally active at night, but if the lights are turned on, they become quiet, and may even go to sleep. This is called 'negative masking', because light is suppressing a behaviour that would normally be present at that time of day. - Nocturnal rodents in a laboratory cage normally sleep in the day, but if the lights are abruptly turned off, the may become active. This is called 'positive masking', because darkness is stimulating a behaviour that would normally be absent at that time of day. Masking: what is the consequence of the direct effect of light and dark on behaviour an animal that has no functional circadian due to brain lesion or gene mutation? - A consequence of the direct effect of light and dark on behaviour is that a light- dark cycle could induce a daily rest-activity rhythm in an animal that has no functional circadian clock, due to a brain lesion or gene mutation. - Such an animal might appear to be entrained by LD, despite lacking any internal clock that could be entrained. This, as you recall, was the issue faced by those (such as de Mairen) who first asked the question, 'are daily rhythms generated endogenously, or are they direct responses to the environment?' Masking: what are several ways to determine whether synchrony of a rest-activity cycle with a LD cycle is due to entrainment or to masking (or both)? - how can you make rhythm by masking? - does LD cycle usually entrain rhythms? if not why? 1. One way is to look at how quickly the rhythm synchronizes to an LD cycle. If synchrony is instantaneous, this is likely due to masking. To confirm this suspicion, you can replace the LD cycle with constant light or dark, and then compare the timing of activity (or sleep) onset on the first day in constant conditions with the onset on the last day of LD. If the two onsets are very different, then masking is likely to explain the timing of the rhythm that is evident in LD. - After a few days in constant conditions, you can fit a regression line to the onset of the daily active period prior to the LD cycle, and then extrapolate it forward to the first day after the LD cycle (see the oblique red lines drawn on the charts in Figure 1). If the timing of activity onsets in DD prior to the LD cycle predicts the phase of onsets in DD after the LD cycle, then the LD cycle cannot be said to have controlled the phase of the circadian clock, and thus cannot be said to have entrained the rhythm. - the LD cycle appears to have produced the observed rhythm entirely by masking, i.e., by inhibition of activity in the light, and stimulation of activity in the dark. The circadian clock, meanwhile, was free-running without entraining. The LD cycle cannot be said to have entrained the rhythm. - LD cycles usually do entrain rhythms, unless something is drastically wrong with the organism (e.g., a brain lesion or gene mutation, or they have lost their eyes), or there is something abnormal about the LD cycle (e.g., it is substantially different from 24h, as on another planet that rotates faster or slower than earth).