Corresponding author e-mail: horaciod@u.washington.edu The master circadian clock located within the hypothalamic suprachiasmatic nucleus regulates an array of diverse circadian rhythms, including the sleep-wake cycle, hormonal rhythms and the phase of peripheral oscillators. This centralized regulation by SCN’s clock warranties the synchronization of circadian rhythms to the light dark (LD) cycle through direct retinal input to the SCN, as well as the internal synchronization of circadian rhythms, characterized by a constant phase relationship between different circadian rhythms within an animal. Neurons within the SCN are single-cell circadian oscillators that oscillate in synchrony under 24-h LD cycles. Exposure to 22-h LD, however, leads to the desynchronization between neurons located within the ventrolateral (vl) and dorsomedial (dm) SCN. This forced desynchronization protocol has become a useful tool to dissect out circadian outputs of the master clock that differentially rely on the activity of each of these SCN subregions. Our laboratory has exploited this animal model to better understand the circadian regulation of core body temperature, sleep stages, the release of melatonin, luteinizing hormone and corticosterone, as well as the decoding of photic input by the SCN neuronal network. Taken together, our results represent the first insight into the neural bases of internal desynchronization, a signature feature of most circadian disorders. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil
H de la Iglesia (Thu,) studied this question.