Sleep and Wakefulness activities: are they intrinsically different?

Wrist actigraphy is a well established procedure used to measure the activity of a subject for long time periods. It is a valuable tool to detect abnormal movement patterns associated with several sleep disorders, including, insomnia, phase lag and periodic limb movements. A potential ability of the actigraphy data, together with other sources of physiological and behavioral information, is the discrimination between sleep and wakefulness states. From a magnitude point of view it is usually simple to do a rough discrimination between these two states. However, the intensity alone can lead to misclassification in the presence of abnormal patterns or in the transition between states. The different characteristics of the movements in sleep and awake states is not simply a matter of magnitude, it is much more that that. Here, the purposeless nature of the movement during the sleep state is assessed and differences, comparing with the wakefulness state, are characterized.1