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Many of us worry about waking up halfway through surgery. The University of
Bristol has an answer. Electrodes on the skull could give an early warning that
the anaesthetic is wearing off (GB 2359367). As a patient goes under, alpha
brain waves between 8 and 12 hertz disappear, only to return as the patient
starts to wake up. The hard bit is detecting the very weak signals fast enough
for the anaesthetist to act. Strangely enough, superimposing a little bit of
random electrical noise to the brain signal will do the trick. This lifts the
level just enough for the circuitry to detect faint alpha patterns on top of the
noise.