Phase Angle of Entrainment in Morning‐ and Evening‐Types under Naturalistic Conditions

Abstract

Differences in morningness-eveningness among humans are commonly ascribed to circadian parameters, such as circadian period and responsivity to environmental time cues, as well as homeostatic sleep drive. Light is the primary synchronizer of the human biological clock, and if circadian differences exist between morning and evening types, they should have different phase angles of entrainment to the light/dark cycle; that is, morning and evening types should have different patterns of light exposure relative to endogenous circadian phase (ECP). When phase angle of entrainment is strictly defined as the relationship between a marker of ECP and the timing of light exposure, such differences have been demonstrated in the laboratory under controlled light/dark cycles and have recently been shown under conditions of spring and summer light exposure outside the laboratory, taking into account the variable intensity of light. Here, we report similar results from a large (n = 66), diverse cohort of morning and evening types across the age span studied at all different times of the year. Differences between morning and evening types in light exposure relative to ECP, indicative of a difference in the phase angle of entrainment to the external light/dark cycle, were found. Specifically, evening types, compared to morning types, had a higher ratio of phase advancing to phase delaying by light. We interpret this as indicating a longer circadian period (τ) in evening types.

Melatonin rhythms in renal transplant recipients with sleep–wake disturbances

“…Figure 1 shows the saliva melatonin profile over night. The mean DLMO was similar to a healthy population: 21.7 h ± 0.95 versus 20.1 ± 1.1 (morning types) and 21.7 h ± 0.95 versus 22.0 ± 1.2 (evening types) (Emens et al, 2009), but the phase angle of DLMO to bedtime was shorter than in this healthy population: 1.2 ± 1.5 hversus 2.2 ± 1.1 (morning types) and 1.2 ± 1.5 hversus 1.6 ± 1.1(evening types) (Emens et al, 2009;Lewy et al, 2006).…”

“…The phase angle describes the relationship between the timing of the biological clock and the timing of external cues (Emens et al, 2009). The phase angle between the DLMO and sleep onset time was calculated by subtracting the DLMO time from the patient's bedtime.…”

The etiology of delayed sleep phase disorder

“…Exposure to light during this portion effectively shifts sleep timing to an earlier time, as determined by the phase response curve (PRC [64]). Lack of exposure to light during this pivotal phase for advancing sleep releases the "brakes" on the tendency to phase delay for individuals with taus longer than 24h [65][66][67].…”

Human Chronotype Is Determined in Bodily Cells Under Real-Life Conditions

“…The mechanism underlying this aspect of human entrainment has not yet been fully understood. It has been suggested that chronotype is likely associated with the endogenous period length because individuals whose clock is running with longer periods tend to be later chronotypes (Brown et al, 2005(Brown et al, , 2008Duffy et al, 2001;Emens et al, 2009;Pagani et al, 2010), but likely also with other properties of the clock driving the circadian rhythms, such as amplitude (Brown et al, 2008). The strength of the cue entraining the clock, i.e., the actual exposure to light, also plays an important role in maintaining the clock in a proper phase relationship with the external light/dark cycle ).…”