Electroencephalography (EEG)

Introduction

Electroencephalography (EEG) is the measurement of electric potentials at the scalp due to currents flowing through scalp tissue. The strength and distribution of currents (and therefore potentials) reflects the intensity and position of activity in the underlying neural tissue. EEG signal is measured between two electrodes, the position of which determines the recorded brain area. Multiple electrodes are typically placed in standard arrangements that cover the entire scalp and allow investigators to observe the activity of the entire brain simultaneously.
EEG is typically recorded as a time-series of potential differences, which can be evaluated visually, or analyzed spectrally, or through the use of source localization methods. The principal spectral components of EEG are divided into the following signal bands: delta (0-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (above 12 Hz) and gamma (above 40 Hz). Many studies have related changes in various spectral components of EEG to specific cognitive functions and clinical conditions.

Applications:

In clinical settings, continuous EEG recordings are used for monitoring sleep and anesthesia, and diagnosis of epilepsy, coma, brain death, and more recently ADHD. In research environments, EEG recordings are used in wide range of applications, including: neuroscience and cognitive psychology research into understanding brain function; Brain-Computer Interfaces to allow control of computers or machines from neural signals; neurofeedback where users are able to train their brains to generate specific activity patterns; neuromarketing where marketing companies seek to tap directly into brain signals to assess subjects’ engagement levels; neuroergonomics where researchers quantify mental workload under various strains; gaming where EEG signals are used to control computer games and toys; etc.

Check out Wikipedia's entry on EEG for a more detailed introduction to EEG.

EEG Spectral Components

Source: Wikipedia's entry on EEG