Considerations towards a neurobiologically-informed EEG measurement of sleepiness

Sleep is a daily experience across humans and other species, yet our understanding of how and why we sleep is presently incomplete. This is particularly prevalent in research examining the online neurophysiological measurement of sleepiness in humans, where several electroencephalographic (EEG) phenomena have been linked with prolonged wakefulness. This leaves researchers without a solid basis for the measurement of sleep need in the individual and complicates our understanding of the nature of sleep. Recent theoretical and technical advances have allowed for a greater understanding of the neurobiological basis of sleep need: sleep need may result from increases in neuronal excitability and shifts in excitation/inhibition balance in neuronal circuits, and this can be directly measured via the aperiodic component of the EEG. Here, we review the literature on EEG-derived markers of sleepiness in humans and argue that changes in these may actually result from changes in aperiodic markers of neural activity. We argue for the use of aperiodic markers derived from the EEG in predicting sleepiness and suggest areas for future research based on these.