Electroencephalography (meaning ‘electrical – brain – study of’) is the process of measuring tiny voltage fluctuations across the scalp. The signal originates from cortical layers close to the brain surface and is produced by the simultaneous firing of many thousands of neurons. When enough neurons fire together in space and time, the signal is strong enough to get through the brain, skull and scalp, and is picked up as a continuous oscillating signal at a number of electrodes.
EEG has traditionally been used to monitor people with epilepsy, sleep disorders and in coma. Analysing the properties of the signals can reveal the psychological state of an individual. States such as arousal, cognitive engagement and relaxation have distinct EEG profiles and can be quantified using signal processing techniques. In a non-clinical research setting, EEG can provide a snapshot as to what the brain is doing immediately after stimulation (e.g. the detection of a face).
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