Quantitative modelling of sleep-wake cycles and application to shiftwork

Svetlana Postnova

Alertness CRC Ltd&

School of Physics, The University of Sydney, Australia

Alumni of the Physics Faculty at the Saratov State University, year 2004

Why model sleep-wake cycles?

• We spend 1/3 of our lives asleep

• Still don’t know why we need to sleep

• Lack of sleep leads to fatigue, accidents, stress, and disease

• 20% of fatal road accidents happen due to driver’s fatigue.

Picture from http://www.sdt.com.au/safedrive-directory-DRIVERFATIGUE.htm

Picture from http://www.coxsoft-art.com/6-methods-to-get-rid-of-fatigue/

Significant risk group - shiftworkers• work irregular hours sleep is disturbed• every 5th person works shifts, e.g. medical

personnel, police force, pilots, …• Poor quality of life• have twice the number of accidents• increased risk of disease, e.g., diabetes,

obesity, heart disease, and cancer.

Why model sleep-wake cycles?

Modelling can help to understand the biological system predict dynamics develop interventions

Photo from http://imannailah.blogspot.com.au/

Biology of sleep-wake cyclesSleep-wake cycles result from interaction between circadian and homeostatic processes

Homeostatic (H) –sleep need increases a function of time awakeCircadian (C)– oscillator with a ~24h period whose phase depends on light input

Borbely and Achermann, 1999, J Biol Rhythms

These processes affect the dynamics of sleep- and wake-active neuronal populations

Saper et al., 2005, Nature

H

C

Quantitative model of sleep-wake cycles

Based on biology

Simulates mean activity of neuronal populations involved in sleep-wake regulation (Neural Field Theory)

Validated against experiments

For full system of equations and detail seePostnova et al., 2013 PLoS one (open access)Postnova et al., 2012, 2014 J Biol Rhythms

For sleep-wake part of the model seePhillips et al., 2007 J Biol RhythsFulcher et al., 2010 J Theor Biol

Postnova et al., 2012, J Biol Rhythms

Quantitative model of sleep-wake cycles: how it works

Sleep Drive, D (mV)

VMA,

(mV)

Fulcher et al., 2010, J Theor Biol

wake

sleepCircadian phase is affected by light input:Light in the morning – advanceLight in the evening – delay

Light input depends on what you do, e.g.Go outside into sunlightStay up late with lights on

Circadian (C)

Homeostatic (H)

Sleep drive (D)

Fulcher et al., 2010, J Theor Biol

wake

sleep

wake

wake

sleep

sleep

Application to shiftwork: effects of shift light intensity

Postnova et al., 2013, PLoS one

Shift – awake

Break – sleep

Light intensity

* Circadian phase marker

room light bright light• Bright light improves adaptation to night

shifts• Amount of sleep increases in bright light

case

Slee

p dr

ive,

D (m

V)

before

after

room light bright light

after

before

• Sleepiness during shifts is significantly reduced in bright light case

Summary

• Quantitative biology-based modelling is a powerful tool that can improve understanding of the system and be applied to real-life problems

• The model of sleep-wake cycles was validated against experiments and also used to study - sleep of different animals, including dolphins and wales- effects of caffeine- effects of alarm clock set at different volume and time- effects of sleep deprivation- adaptation to jetlag- dynamics on different types of shift schedules

For references see http://sydney.edu.au/science/physics/research/complex-systems/brain-dynamics/index.shtml or google “brain dynamics complex systems USYD”

Write to spostnova@sydney.edu.au for questions

Acknowledgements

Prof. Peter Robinson (University of Sydney, Australia)Dr Andrew Philips (Harvard University, USA)Dr Ben Fulcher (Monash University, Australia)Dmitry Postnov (University of Copenhagen, Denmark)Romesh Abeysuriya (University of Sydney, Australia)Andrew Layden (University of Sydney, Australia)

And many other people who worked on the model

Funded by Australian Research Council and National Health and Medical Research Council through the Centre for Integrated Research and Understanding of Sleep (CIRUS)