Fig. 4: Wake effort.

In the neuronal interpretation of the two-process model, during wake, once the upper threshold has been reached to remain awake requires effort i.e. additional input to wake active neurons which shifts the position of the upper threshold. During sleep, if awoken while homeostatic sleep pressure is above the upper threshold, then again effort is required to shift the upper threshold (grey dashed lines). Regions in which wake effort is needed are highlighted in magenta. As in Fig. 3 we have drawn the `active' parts of the thresholds in dark grey and the `inactive' parts of the thresholds in light grey.