Evoked Potentials (EP)
What is an evoked potentials study?
Evoked potentials studies measure electrical activity in the brain in response to stimulation of sight, sound, motor impulse or touch. Stimuli delivered to the brain through each of these senses evoke minute electrical signals. These signals travel along the nerves and through the spinal cord to specific regions of the brain and are picked up by electrodes, amplified, and displayed for a doctor to interpret.
Visual evoked potential (VEP) test. This test can diagnose problems with the optic nerves that affect sight. Electrodes are placed along your scalp and the electrical signals are recorded as you watch a checkerboard pattern flash for several minutes on a screen.
Somatosensory evoked potential (SSEP) test. This test can detect problems with the spinal cord as well as numbness and weakness of the extremities. For this test, electrodes are attached to your wrist, the back of your knee, or other locations. A mild electrical stimulus is applied through the electrodes. Electrodes on your scalp then determine the amount of time it takes for the current to travel along the nerves to the brain.
Auditory evoked potential (AEP) test. This test can diagnose hearing ability and can point to possible brainstem tumors or multiple sclerosis. Electrodes are placed on your scalp and earlobes and auditory stimuli, such as clicking noises and tones, are delivered to one ear.
Motor evoked potential (MEP) elicited in peripheral muscles by transcranial magnetic stimulation over human motor cortex is one of the hallmark measures for non-invasive quantification of cortical and spinal activity in clinical neuroscience. Clinical uses of MEPs include as a tool for the diagnosis and evaluation of multiple sclerosis and as a prognostic indicator for stroke motor recovery.