Chapter 10 - Background

Summary

Symmetry: it may be symmetric, mildly asymmetric, or markedly asymmetric. Mild asymmetry of the dominant hemisphere may be physiologic. Continuity: it may be continuous, nearly continuous, discontinuous, or burst-suppressed. Attenuation is the periodic dampening of amplitudes by less than half the remaining background, while suppression is when the amplitude falls below 10 uV. Voltage: it may be normal (above 20 uV), low voltage (20-10 uV), or suppressed (less than 10 uV). Organization: a well-organized background has an anterior-posterior gradient, predominantly alpha frequencies, and a reactive posterior dominant rhythm (PDR). The loss of either or all these features results in a deterioration in background organization. Variability and reactivity: variability refers to spontaneous changes in the background, while variability refers to changes in response to external stimulation. Always specify the stimulation used and advance it in a graded manner. Variability and reactivity of the background are associated with favorable clinical outcomes. Presence of stage II sleep architecture such as spindles and K complexes should be noted