Electroencephalography (EEG) is the measurement of electrical activity in the brain. Measurement and graphical representation is recorded via electrodes that are placed on the scalp. Electrical activity in the brain passes through the electrodes, which are connected to an EEG amplifier. Signals within the brain are low in amplitude, so an EEG amplifier is used to ‘amplify’ brain activity and make it more visible. Brain activity is then recorded via an EEG amplifier and represented graphically in the form of waves also known as brainwaves.
When neurons or nerve cells fire simultaneously throughout the brain, the action potentials produced cause a significant change in electrical charge that is large enough to be recorded by electrodes. These electrodes are conductors that are placed along the surface of a thoroughly-cleaned scalp. They allow electrical activity to pass through them and, by placing numerous electrodes onto the scalp, electrical activity within different areas of the brain can be recorded at the same time. Electrodes are connected via a cable to an EEG amplifier, such as a polygraph, and it is this machine that records the physiological changes that occur within different areas of the brain.
An EEG recording may be either monopolar or bipolar. A monopolar recording occurs when an individual electrode measures brain activity in comparison with an indifferent and remotely-located electrode, whereas a bipolar recording measures brain activity between a pair of electrodes. Measurement occurs in the form of waves and is made up differing frequencies. These frequencies are grouped as either falling within the alpha (8 -13 hertz), beta (13-30 hertz), delta (0.5-2 hertz) or theta (4-7 hertz) range. An EEG amplifier allows brainwaves to be recorded, often resulting in particular waveforms that are characteristic to certain behaviors; for example, when an individual is relaxed, alpha activity is typically recorded.
EEG’s have been implemented to record brain activity during different behaviors. They have been used to record brain activity during sleep and have also been used to measure epileptic activity such as seizures. Epilepsy is a condition characterized by recurrent seizures that are either partial or generalized. Partial seizures occur in one hemisphere of the brain from a specific area, whereas generalized seizures begin in various areas and result in a loss of consciousness. EEG recordings help to distinguish whether a seizure is either partial or generalized by measuring the significant change in brain activity that occurs during the epileptic activity.