Evoked Potential (EP)

Evozierte Potentiale Neurozentrum Aarau

What is evoked potential?

EP tests involve repeating a certain stimulus. The electrical response of the brain or spinal cord to this stimulus is measured at a specific point on the head or spine and deduced from the other electrical activities of the brain. This involves placing the electrode on the head, precisely over the part of the brain that responds to the stimulus. This simple method makes it possible to measure disruptions or damage to the conduction paths (nerves) in our bodies. Compared to spontaneous potentials (e.g. EEG) signals, evoked potentials are of lower amplitude. The stimuli must be applied repeatedly to take a reading.

Visual evoked potentials (VEP) test the optic tracts

This makes it possible to test the conduction of nerve impulses transmitted along the optic tract. The optic tract is stimulated with a checkerboard pattern that rapidly changes its black and white profile at regular intervals. The patient observes the pattern on a screen, first with one eye and then the other. Using electrodes attached to the head of the patient, the doctor records the electric potentials triggered in the visual cortex.

This is an important method, for example, in the diagnosis of inflammatory or circulation-related optic nerve and optic tract changes (e.g. optic neuritis in multiple sclerosis patients).

Somato-sensory evoked potentials (SSEP) test the sensory pathways.

SSEPs makes it possible to evaluate the central and peripheral sensory pathways,
allowing the doctor to test the transmission of sensations from the arms and legs via the spinal cord and to the brain. This is done with short, repetitive stimuli on the ankles and wrists. The signals that are triggered are measured on the head or over the vertebral canal.

This method is used, for example, to accurately detect sensory disturbances (e.g. in cases of multiple sclerosis).

Motoric evoked potentials (MEP) test the pathways responsible for movement.

MEPs monitor the transmission of nerve impulse that are responsible for controlling muscle movements from the brain via the spinal cord to the extremities (arms and legs).

During the examination, the head, neck or lumbar region of the patient is placed in a strong magnetic field, which stimulates the corresponding region of the cerebral cortex or spinal cord. This results in brief, involuntary muscle twitching in the arms or legs, depending on the part of the brain being stimulated. Some patients find this uncomfortable, but it is not dangerous (the doctor will be aware of the few rare contraindications and should take these into account).