Irregular slow waves known as delta waves, for example, arise from the vicinity of a localized area of brain damage. Electroencephalography provides a means of studying how the brain works and of tracing connections between one part of the central nervous system and another. Its effectiveness as a research tool, however, is limited because it records only a small sample of electrical activity from the surface of the brain. Many of the more complex functions of the brain, such as those that underlie emotions and thought, cannot be related closely to EEG patterns. Electroencephalography has proved more useful as a diagnostic aid in cases of serious head injuries, brain tumors, cerebral infections, epilepsy, and various degenerative diseases of the nervous system.
Some patients have other disorders that lead to problems with esophageal contraction.
For example, many patients with scleroderma have abnormal esophageal manometry tests. Esophageal spasms can cause severe chest pain that mimics heart disease. These spasms can be detected by appropriate manometry testing. This test is performed when a patient is asked to swallow a thin tube that is placed through the nose into the esophagus where it remains for 24-hours. It is similar in size to a piece of spaghetti.