They must choose the most appropriate combination of instrument controls and electrodes to correct for mechanical or electrical interference that come from somewhere other than the brain, such as eye movement or radiation from electrical sources. Increasingly, technologists perform EEG's in the operating room, which requires that they understand anesthesia's effect on brain waves. For special procedure EEG's, technologists may secure electrodes to the chest, arm, leg, or spinal column to record activity from both the central and peripheral nervous systems. In ambulatory monitoring, technologists monitor the brain, and sometimes the heart, while patients carry out normal activities over a 24-hour period. Then they remove the small recorder carried by the patients and obtain a readout.
Technologists review the readouts, selecting sections for the physician to examine.
After the electrodes have been attached, they set the instrument for the type and intensity of the stimulus, increase the intensity until the patient reacts, and note the sensation level. The tests may take from 1 to 4 hours. For nerve conduction tests, used to diagnose muscle and nerve problems, technologists place electrodes on the patient's skin over a nerve and over the muscle. Then they stimulate the nerve with an electrical current and record how long it takes the nerve impulse to reach the muscle. Technologists who specialize in and administer sleep disorder studies are called polysomnographic technologists.