Introduction

Chapter 1 Introduction

Electroencephalography (EEG) remains one of the principle tools in the practice of clinical neurology. Notwithstanding the development of increasingly sophisticated imaging techniques over the years, including computed tomography (CT) scanning, magnetic resonance imaging (MRI), nuclear medicine imaging, and newer functional MRI techniques, the use of EEG in the assessment of neurological disorders continues to increase. The information learned from EEG testing differs in a number of ways from what is learned from radiological images such as MRI scans. Whereas MRI primarily furnishes anatomical information as a snapshot in time, EEG captures electrical information over time. Just as an X-ray image of the heart does not tell us whether a patient’s heart is beating quickly or slowly, information easily learned from an electrocardiogram, likewise CT and MRI scans of the brain do not give direct information regarding electrical irritability in the brain or even indicate whether the patient is awake or asleep. Thus radiological imaging studies and electroencephalography are complementary techniques.

Electroencephalography is used in a variety of clinical situations, but the large majority of EEGs are obtained as a part of the evaluation of seizures or epilepsy. Estimates of the population prevalence of epilepsy range between 0.5% and 1%, suggesting that at least 2 million people in North America have epilepsy. EEG is also useful in the evaluation of confusional states and coma, and it can play an important role in separating psychiatric illness from organic disease.

Electroencephalography is a relatively young science. One hundred years ago, it was not yet a settled fact that there was electrical activity in the human brain. In 1875, Richard Caton was the first to report an observation of electrical activity from the brains of monkeys and rabbits, though techniques available at the time did not allow him to record these waveforms for posterity. Caton made his observations using a device called Thomson’s mirror galvanometer (Caton, 1877). Oscillations in the mirror affixed to a galvanometer caused movements of a beam of light the mirror reflected on the wall of his laboratory. His report that “Feeble currents of varying direction pass through the multiplier when the electrodes are placed on two points of the external surface, or one electrode on the grey matter, and one on the surface of the skull” is considered the first description of an EEG wave (Caton, 1875). Thereafter, successful recordings were made by Caton and others from the brains of dogs, monkeys, rabbits, and cats, although some still claimed that the recorded waves were related to the pulsations of cerebral blood vessels rather than to brain electrical activity.

Hans Berger, considered the father of modern Electroencephalography, was the first to record EEG in humans (see Figure 1-1) while working as a professor of psychiatry at the University of Jena in Germany. His previous work included precise measurements of cerebral pulsations in both animals and humans and, later, the measurement of brain temperature variations in animals to determine whether temperature fluctuated in different behavioral states. His first attempts at recording brain waves in 1924 were carried out using a string galvanometer designed to record electrocardiograms (see Figure 1-2). The initial recordings were made in subjects with areas of missing cranial bone, either from palliative trepanations (creation of a window in the skull bone) for relief of increased intracranial pressure from brain tumors or from skull defects related to injuries sustained during the First World War. Because of these patients’ skull defects, the needle electrodes he used could be placed only a few millimeters away from the brain surface.

Figure 1-1 Hans Berger at age 52 (1925), one year after he began his work on the human electroencephalogram.

(Courtesy Mrs. Ursula Berger. With permission, from Berger H, Gloor P. On the electroencephalogram of man; the fourteen original reports on the human electroencephalogram [Gloor P, translator and editor], Amsterdam and New York, Elsevier, 1969.)

Figure 1-2 This photograph shows one of the first attempts at recording the electroencephalogram in humans. The patient had undergone a left-sided trepanation. The recording attempt was made with silver electrodes secured to the scalp with adhesive tape but was unsuccessful. This patient was recorded sitting up; later patients were studied lying on a couch with glass legs for electrical isolation.

(With permission, from Berger H, Gloor P. On the electroencephalogram of man; the fourteen original reports on the human electroencephalogram [Gloor P, translator and editor], Amsterdam and New York, Elsevier, 1969.)

In his first report, titled “On the Electroencephalogram of Man” and published in 1929, Berger outlines the path toward his first successful observation of the EEG of man (which he did not, at the time, have the equipment to record). The observation was made in 1924 in a 17-year-old boy who had undergone palliative trepanation over the left cerebral hemisphere for a brain tumor. The first published recorded rhythm, shown in Figure 1-3, was obtained in a 40-year-old man who had had a large bone flap removed to relieve pressure from a brain tumor. The recording was made with needle electrodes placed subcutaneously which, in this patient, represented the epidural space. The patient died from his tumor a few weeks later.