They must choose the most appropriate combination of instrument controls and electrodes, to correct for mechanical and electrical interference from somewhere other than the brain, such as eye movement or radiation from electrical sources. Increasingly, technologists perform EEGs in the operating room, which requires that they understand anesthesia's effect on brain waves. For special procedure EEGs, 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 attach small recorders to patients to monitor the brain, and sometimes the heart, while patients carry out normal activities over a 24-hour period. They then remove the recorder and obtain a readout.
Technologists review the readouts, selecting sections for the physician to examine.
Using evoked potential testing, technologists measure sensory and physical responses to specific stimuli. After attaching electrodes to the patient, they set the instrument for the type and intensity of the stimulus, increase the intensity until the patient reacts, and note the sensation level. For nerve conduction tests, used to diagnose muscle and nerve problems, technologists place electrodes on the patient's skin over a nerve and over a 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 .