Circadian phase-shifting by light: Beyond photons
Circadian entrainment to the solar light:dark schedule is thought to be maintained by a simple photon counting method. According to this hypothesis, the pacemaker adjusts the phase of the body’s endogenous rhythms in accordance to the intensity and duration with which it encounters a perceived twili...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2018-06-01
|
| Series: | Neurobiology of Sleep and Circadian Rhythms |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2451994417300366 |
| _version_ | 1818955747541647360 |
|---|---|
| author | Sevag Kaladchibachi David C. Negelspach Fabian Fernandez |
| author_facet | Sevag Kaladchibachi David C. Negelspach Fabian Fernandez |
| author_sort | Sevag Kaladchibachi |
| collection | DOAJ |
| description | Circadian entrainment to the solar light:dark schedule is thought to be maintained by a simple photon counting method. According to this hypothesis, the pacemaker adjusts the phase of the body’s endogenous rhythms in accordance to the intensity and duration with which it encounters a perceived twilight signal. While previous data have generally supported the hypothesis, more recent analysis has codified other factors besides irradiance that influence the magnitude of resetting responses to light delivered within the same phase of the circadian cycle. In particular, the frequency with which light is alternated with darkness, or whether it’s packaged in millisecond flashes versus continuous blocks, can significantly alter the dose-response relationship. Here, we used a drosophilid model to test whether circadian photon-counting trends can be broken with light administration protocols spanning just 15 minutes. In the early part of the delay zone, a 15-min continuous light pulse was fragmented until it could no longer produce a full-magnitude shift of the flies’ locomotor activity rhythms. The remaining exposure was then reorganized along various fractionation schemes that employed pulses with different widths and interstimulus intervals. Our results suggest that the pacemaker integrates the phase-shifting effects of equiluminous light differently depending on the stimulus pattern with which light is made available. For example, despite having fewer photons, certain ratios of light and darkness could be optimized on a timescale of seconds and minutes so as to achieve pacemaker resetting close to par with steady luminance. These data provide further evidence that the circadian pacemaker’s responses to light entail more than photon counting and motivate continued discussion on how phototherapy can be best optimized in clinical practice to improve conditions linked to circadian impairment. Keywords: Light, Circadian, Phase shift, Entrainment, Phototherapy |
| first_indexed | 2024-12-20T10:42:59Z |
| format | Article |
| id | doaj.art-368e4e75b18c4fe7bb0d0256a4b6d1b5 |
| institution | Directory Open Access Journal |
| issn | 2451-9944 |
| language | English |
| last_indexed | 2024-12-20T10:42:59Z |
| publishDate | 2018-06-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Neurobiology of Sleep and Circadian Rhythms |
| spelling | doaj.art-368e4e75b18c4fe7bb0d0256a4b6d1b52022-12-21T19:43:31ZengElsevierNeurobiology of Sleep and Circadian Rhythms2451-99442018-06-015814Circadian phase-shifting by light: Beyond photonsSevag Kaladchibachi0David C. Negelspach1Fabian Fernandez2Department of Psychology, University of Arizona, Tucson, United StatesDepartment of Psychology, University of Arizona, Tucson, United StatesDepartment of Psychology, University of Arizona, Tucson, United States; Department of Neurology, University of Arizona, Tucson, United States; McKnight Brain Research Institute, University of Arizona, Tucson, United States; BIO5 Institute, University of Arizona, Tucson, United States; Corresponding author at: Department of Psychology, University of Arizona, 1501 N. Campbell Avenue, Life Sciences North, Room 349, Tucson, AZ 85724, United StatesCircadian entrainment to the solar light:dark schedule is thought to be maintained by a simple photon counting method. According to this hypothesis, the pacemaker adjusts the phase of the body’s endogenous rhythms in accordance to the intensity and duration with which it encounters a perceived twilight signal. While previous data have generally supported the hypothesis, more recent analysis has codified other factors besides irradiance that influence the magnitude of resetting responses to light delivered within the same phase of the circadian cycle. In particular, the frequency with which light is alternated with darkness, or whether it’s packaged in millisecond flashes versus continuous blocks, can significantly alter the dose-response relationship. Here, we used a drosophilid model to test whether circadian photon-counting trends can be broken with light administration protocols spanning just 15 minutes. In the early part of the delay zone, a 15-min continuous light pulse was fragmented until it could no longer produce a full-magnitude shift of the flies’ locomotor activity rhythms. The remaining exposure was then reorganized along various fractionation schemes that employed pulses with different widths and interstimulus intervals. Our results suggest that the pacemaker integrates the phase-shifting effects of equiluminous light differently depending on the stimulus pattern with which light is made available. For example, despite having fewer photons, certain ratios of light and darkness could be optimized on a timescale of seconds and minutes so as to achieve pacemaker resetting close to par with steady luminance. These data provide further evidence that the circadian pacemaker’s responses to light entail more than photon counting and motivate continued discussion on how phototherapy can be best optimized in clinical practice to improve conditions linked to circadian impairment. Keywords: Light, Circadian, Phase shift, Entrainment, Phototherapyhttp://www.sciencedirect.com/science/article/pii/S2451994417300366 |
| spellingShingle | Sevag Kaladchibachi David C. Negelspach Fabian Fernandez Circadian phase-shifting by light: Beyond photons Neurobiology of Sleep and Circadian Rhythms |
| title | Circadian phase-shifting by light: Beyond photons |
| title_full | Circadian phase-shifting by light: Beyond photons |
| title_fullStr | Circadian phase-shifting by light: Beyond photons |
| title_full_unstemmed | Circadian phase-shifting by light: Beyond photons |
| title_short | Circadian phase-shifting by light: Beyond photons |
| title_sort | circadian phase shifting by light beyond photons |
| url | http://www.sciencedirect.com/science/article/pii/S2451994417300366 |
| work_keys_str_mv | AT sevagkaladchibachi circadianphaseshiftingbylightbeyondphotons AT davidcnegelspach circadianphaseshiftingbylightbeyondphotons AT fabianfernandez circadianphaseshiftingbylightbeyondphotons |