Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Higher Nervous Activity
Electroencephalography

Electroencephalography (EEG) is a method for recording the bioelectrical activity of the Brain. During this Procedure, electrodes are placed on the scalp to detect fluctuations in the brain's electrical potentials. These signals are subsequently amplified 1 to 2 million times and recorded by specialized devices onto a medium (such as paper). The brain's bioelectrical activity recorded via EEG typically exhibits a wave-like pattern (Fig. 16.1). These waves vary in shape, frequency, and amplitude. In a healthy individual, a-waves (alpha waves) predominate; their frequency ranges from 8 to 12 oscillations per second, with an amplitude of 10 to 50 µV (up to 100 µV). ß-Waves (beta waves) have a frequency of 15 to 32 oscillations per second, but their amplitude is several times lower than that of a-waves. At rest, a-waves predominate in the posterior Regions of the brain, whereas P-waves are localized primarily in the frontal areas. Slow δ-waves (delta waves) and Q-waves (theta waves) appear in healthy adults as they fall asleep. Their frequency is 0.5 to 3 oscillations per second for δ-waves and 4 to 7 oscillations per second for 0-waves. The amplitude of these slow rhythms ranges from 100 to 300 µV.

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Fig. 16.1. Human Electroencephalogram during periods of wakefulness and Sleep:

a — EEG during wakefulness; b — EEG during slow-wave sleep; c — EEG during fast-wave sleep

Electroencephalography is widely used in clinical practice. It helps determine the side of brain damage, the tentative localization of a pathological focus, and distinguishes between diffuse and focal pathological processes. The method is of invaluable importance in the Diagnosis of Epilepsy.