The Chronobiology and Sleep Laboratory (CSL) conducts research on circadian rhythms and sleep patterns. The circadian (about a day) system plays an important role in regulating cognitive performance and sleep-wake timing. Circadian rhythms of behavior and physiology are normally synchronized with the rising and setting of the sun. In response to shift work or jet lag, however, circadian rhythms can become misaligned with the sleep-wake cycle and/or solar day. This results in sleep disturbances and impaired neurobehavioral performance. Additionally, many individuals are habitually exposed to sleep deprivation due to lifestyle choices, environmental pressures, or sleep disorders.

The CSL aims to 1) understand the impact of circadian desynchrony and sleep insufficiency on performance and health, and 2) develop approaches for optimizing circadian entrainment and improving sleep behavior. There are three major research themes in the CSL:

Non-visual photoreception

Light is the primary stimulus that synchronizes the human circadian system. For decades, it was assumed that rod-cone photoreceptors that mediate vision also drive circadian light resetting. In recent times, one of the most exciting stories to unfold has been the discovery and characterization of retinal ganglion cells that contain the photopigment melanopsin. Melanopsin cells are intrinsically photosensitive and respond preferentially to blue light, but they also receive input from rods and cones. The melanopsin cells are responsible for mediating several non-visual light responses including circadian resetting, melatonin suppression, and pupillary constriction. The CSL studies the contributions of melanopsin and visual photoreceptors to non-visual light responses by manipulating the irradiance, duration, and wavelength of light exposure. We also study non-visual light responses in patients with different types of retinal diseases (link to CSL publications).

Circadian rhythms, sleep, and metabolism

The circadian system plays a key role in regulating energy metabolism. Notably, shift workers are at increased risk of obesity and metabolic disorders, and this is thought to arise in part from circadian misalignment with the rest-activity cycle and chronic sleep loss. Sleep deprivation is also associated with impaired glucose homeostasis, and has been implicated in the development of Type 2 diabetes. The CSL studies the role of circadian rhythms and sleep in energy metabolism. In previous work, we characterized plasma lipids that are circadian-regulated and influenced by exposure to sleep deprivation

Monitoring and predicting cognitive vulnerability to sleep deprivation

Sleepiness is a major cause of vehicular accidents. Technologies that monitor changes in sleepiness can potentially be used to warn individuals when they are at increased risk of falling asleep, hence preventing an accident from taking place. Some people are also inherently at greater risk of having lapses in attention when exposed to sleep loss, due to trait-like individual differences in cognitive vulnerability to sleep deprivation. The CSL has conducted research on behavioral and physiologic measures that carry information about a person’s current vigilance state, as well as his/her relative vulnerability to the effects of sleep deprivation


The CSL conducts both laboratory and field studies. The CSL routinely uses the following research methods:
  • Polysomnography for sleep staging and for assessing wake-dependent changes in the electroencephalogram
  • Constant routine procedure for assessing circadian rhythms
  • Evaluation of circadian phase markers including core body temperature, melatonin, and cortisol
  • Eye-tracking for ocular-based measures of drowsiness
  • Pupillometry for evaluating pupillary responses to light
  • Neurobehavioral tests for assessing sustained attention, working memory, processing speed, hand-eye coordination, and mood/fatigue
  • Actigraphy monitoring of sleep-wake patterns in field studies


The CSL conducts research that has broad implications for health and safety. Our work has therefore been supported by diverse sources of funding including medical research grants, military contracts, and industry partnerships. Many of our research initiatives were supported by the Duke-NUS Signature Research Program funded by the Agency for Science, Technology, and Research, and the Ministry of Health, Singapore. Below we highlight additional sources of support, both past and present, by research topic:

  • Non-visual photoreception: National Medical Research Council, Singapore; and the Singapore National Eye Center Health Research Endowment Fund.
  • Circadian rhythms and metabolism: SingHealth Foundation, Singapore.
  • Shift work and cognitive vulnerability: Defense Advanced Research Projects Agency (DARPA), USA; Defense Science Technology Agency, Singapore; Republic of Singapore Navy; Defense Science Organization (DSO) National Laboratories, Singapore.
  • Sleep insufficiency in adolescents: National Research Foundation, Singapore; Far East Organization
  • Sleep deprivation and alcohol: Ministry of Education, Singapore; Defense Science Technology Agency, Singapore
© Chronobiology and Sleep Laboratory 2017