Journal: Current Psychiatry Reports

Article Title: The Emerging Circadian Phenotype of Borderline Personality Disorder: Mechanisms, Opportunities and Future Directions

doi: 10.1007/s11920-021-01236-w

Figure Lengend Snippet: Schematic of the circadian timekeeping system. The circadian time-keeping system is governed by the central clock of the SCN. Efferent SCN signals (blue) coordinate time-keeping among other circadian oscillators in the brain and peripheral organs, establishing a stable phase relation between endogenous circadian oscillators. This network generates an internally stable 24 h cycle that represents the internal day of the circadian system. Circadian signals used to determine the phase of the circadian clock involve robustly oscillating rhythms in core body temperature (CBT), inter-beat interval heart-rate variability (HRV) and plasma melatonin and cortisol. To impart a functional advantage of anticipating time related changes in the environment, the circadian clock is entrained to the external light-dark cycle which serves as the primary zeitgeber to the circadian clock. Retinal photic zeitgeber input signals (red) are transduced to the SCN via a dedicated non-visual circuit known as the retinohypothalamic tract (RHT). Hence, through entrainment, the SCN synchronises its period to that of the 24 h day. Interaction between the 24 h period of the external day (T) and that of the endogenous internal day (tau) generates the circadian phase of entrainment ( ψ ). The phase range at which the internal day coalesces with the external 24 h day gives rise to different ψ expressed as earlier or later chronotypes. Chronotype assessed via the midsleep time displays an approximately normal distribution in the population and is a trait that influences behavioural routines of rest and activity. Manipulation of zeitgeber exposure can produce phase shifts in ψ . Early morning exposure to bright light produces a phase advance of the circadian clock, whereas evening exposure produces a phase delay of the circadian clock. Using agents that adjust the phase of the circadian clock is the basis of chronotherapy. Endocrine and temperature reference ranges shown in figure are adapted from Hickie et al. or based on laboratory estimates. RMSSD ranges are based on ambulatory ECG recordings

Article Snippet: The circadian phase of entrainment can be estimated using actigraph assessed acrophase, midsleep time or non-parametric circadian rhythm parameters [ , ].

Techniques: Clinical Proteomics, Functional Assay, Activity Assay