Phase response curves to light and to melatonin Essay

Phase response curves to light and to melatonin - Essay Example In human light PRC (Figure 1), the y-axis of the PRC shows the direction and relative magnitude of the phase shift in hours induced by light exposure (solid line). Circadian Time Zero (CT0) corresponds to 11:00 am and CT22-CT18 is the duration for day time activity. The black bar, which indicates the time period between 12:00 midnight – 8:00am, along x-axis represents the duration for sleeping. Bright light treatment causes the phase-delay of circadian phase, which is represented by the area from CT10 to CT18. During this period, bright light treatment causes later onset of sleeping/awakening cycle. As time progresses from CT10, stronger effect on phase-delay is observed. At CT18, this phase-delay effect is changed dramatically to phase-advancing effect. The peak phase-advancing effect coincides with sunrise. From CT18 to CT3, bright light treatment induces phase-advancing effect, causing earlier onset of sleeping / awakening cycle. This effect gradually decreases from CT19 to CT3. As noted in the graph, little or no effect is observed when bright light treatment is applied from CT14 to CT20, in which this time period corresponds to 2:00pm to 8:00pm. The intensity of the light used in bright light treatment can have direct effect on the magnitude of the phase advancement or delay. ... After this time point, this effect decreases to the lowest point to CT12. It should be noted that during this time period, bright light treatment has no phase-shifting effect on circadian rhythm. From CT18 to CT0, melatonin administration induces a phase-delay effect on circadian rhythm, however, this effect is relatively small when compared with the phase advancing effect induced by bright light treatment. From 2 hours before the onset of sleeping (CT12) onwards until time of sunrise (CT18), administration of melatonin does not exert any effect on circadian rhythm. This time duration coincides with phase delaying effect of bright light treatment. b. Using this knowledge of the phase response curves to light and to melatonin, design a protocol to alleviate the effects of jet lag when travelling from London Singapore (8 time zones eastward) The flights for travelling from London to Singapore are available both in the morning and at night. The local time in Singapore is ahead of London by 8 hours (8 time zones eastward). Assuming there are two flights travelling from London to Singapore, one flight has the depart time at 11:00 am (London local time) and arrive in Singapore at 7:00 am (Singapore local time, one day ahead); the other flight departs at 22:00 pm (London local time) and arrives at 18:00 pm (Singapore local time, one day ahead). The total duration of the flight is approximately 13 hours. The circadian rhythm may be entrained by advance or delay the sleep/awake cycle and both intake of melatonin at about 4 hours before to its natural peak in the circadian cycle or bright light treatment may induce an advance response (3). The following protocol is devised from