The Development of Circadian Rhythms in Human Infants

For the purpose of this study, the protocol had to be „user friendly‟ and promote
maximum participation so a simple method of measuring sleep (actigraphy) was
employed.
Actigraphy allows home monitoring of infant sleep. The actiwatch is a lightweight,
small, simple to use device which measures movement by use of an accelerometer.
Using algorithms (mainly written for adult work) it translates movement counts into
estimates of wake and rest (see methods section 2.7). The algorithms are written
specifically for adult use. They do not allow sleep to be separated into different sleep
states as it gives only a crude measure of movement rather than a precise measure of
sleep (Acebo et al., 1999, Sadeh & Acebo, 2002, Morgenthaler et al., 2007). An
actiwatch model, however, has been developed for use in infants which divides sleep
into active and quiet sleep (Sadeh et al., 1989).
Another drawback of actigraphy it is less able to differentiate between movement
artefact during sleep from movement during „genuine‟ wakefulness. Movement in
infants induced by the carer (such as rocking) may also be scored incorrectly as a
period of wakefulness when actually the infant is asleep. This is less of an issue in
adult research as movement generated is by study participant only.
Actigraphy has variable correlation with specific sleep parameters. In adults it may
have up to 90% agreement with polysomnography for detecting periods of sleep
(Paquet et al, 2007, Morgenthaler et al, 2007). This is achieved in children at around
9 months of age. The use of actigraphy in younger infants have reportedly much
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