1. A. “10-20” is a measurement system designed to reliably reproduce electrode positions on different patients, regardless of head size. Electrodes are placed at intervals of either 10 or 20 percent of the hemi-circumference of the head. (Courtesy of Dr. Jay S. Pathmanathan.) B. Each channel represents the amplified recording of voltage changes over time between two electrodes. Normal alpha (8 to 12 per second) activity is present posteriorly (bottom channel). The top channel contains a large blink artifact. Note the striking reduction of the alpha rhythm with eye opening (arrow). C. Photic driving. During stroboscopic stimulation of a normal subject, a visually evoked response is seen posteriorly after each flash of light (signaled on the bottom channel). D. Stroboscopic stimulation at 14 flashes per second (bottom channel) has produced a photoparoxysmal response in this epileptic patient, evidenced by the abnormal spike and slow-wave activity toward the end of the period of stimulation. E. Large, slow, irregular delta waves are seen in the right frontal region (channels 1 and 2). In this case a glioblastoma was found in the right cerebral hemisphere, but the EEG does not differ basically from that produced by a stroke, abscess, or contusion. F. An EEG showing focal spike-and-wave discharges over the right frontal region (channels 1 to 3). The box isolates a single spike–wave transient. G. Phase reversal is shown between electrode pairs, F7-T3 and T3-T5, implying that the site of the spike generator is under the T3 electrode. (Courtesy of Dr. Jay S. Pathmanathan.) H. Localization of a spike in a montage that utilizes the right ear (A2) as a reference electrode. The amplitude of the transient at T3 is greater than at other locations, implying that the source of the spike is closest to the T3 electrode. (Courtesy of Dr. Jay S. Pathmanathan.) I. Absence seizures, showing generalized 3-per-second spike-and-wave discharge. The abnormal activity ends abruptly and normal background activity appears. J. Deep coma following cardiac arrest, showing electrocerebral silence. With the highest amplification, electrocardiogram (ECG) and other artifacts may be seen, so that the record is not truly “flat” or isoelectric. However, no cerebral rhythms are visible. Note the ECG (lower channel). K. Grossly disorganized background activity interrupted by repetitive “pseudoperiodic” discharges consisting of large, sharp waves from all leads about once per second. This pattern is characteristic of Creutzfeldt-Jakob disease. L. Advanced hepatic coma. Slow (about 2 per second) waves have replaced the normal activity in all leads. This record demonstrates the triphasic waves often seen in this disorder.
Source: Diagnostic Testing in Neurologic Disease, Adams and Victor's Principles of Neurology, 11e
Citation: Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor's Principles of Neurology, 11e; 2015 Available at: Accessed: October 12, 2017
Copyright © 2017 McGraw-Hill Education. All rights reserved