The relation between electrical brain activity, fatigue and sleepiness is complex and not well understood. Fatigue and sleepiness are based on two different psychological constructs. A model that distinguishes between both constructs is outlined. According to this model it is possible to predict fatigue as well as sleepiness for human operators.
While it seems extremely difficult to define a scientific approach for the investigation of fatigue through EEG measurements, sleepiness is clearly related to changes in electrical brain activity.
A standard physiological method to assess sleepiness is the so-called polysomnographic recording that includes EEG. In particular, the assessment of micro-sleep events, the so-called MSLT (Multiple Sleep Latency Test) that has also clinical relevance, and the determination of sleep onset latencies are related to the concept of sleepiness and are based on EEG measures.