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Effect of somnolence on electroencephalography
In healthy subjects, electroencephalography (EEG) shows distinct characteristics correlated to the level of somnolence experienced by a subject. To better measure these changes, and thus the level of somnolence, a common approach is to analyze the low frequency band (for example delta, alpha and theta waves) of the electroencephalographic signal. EEG frequency analysis is a standard approach that can provide insights into sleep and waking brain activity. While being in a drowsy state, the EEG shows higher slow frequency activity than compared to a rested waking condition. These changes may be used to track the somnolence state of a subject using only a handful of electrodes applied on the scalp and paired with an EEG recorder. For example, this very same technique has been used during long haul flights in aviation pilots to objectively measure their somnolence during the flight. Similar approaches are used also for car drivers somnolence detection.