Specialized Laboratory for Evoked Potentials
Book an appointmentWhat are Evoked Potentials?
In these examinations, a specific stimulus is repeatedly applied. On the head or along the spine, the electrical response of the brain or spinal cord to this stimulus is recorded over a specific point and calculated separately from the other electrical activities of the brain. For this purpose, the electrode on the head is placed precisely over the brain area where these stimuli can be perceived. Using this simple method, interruptions or damage to the conduction pathways (nerves) in our body can be measured. Compared to spontaneous potentials (e.g., EEG), evoked potentials are signals with low amplitude. In order to record them, the stimuli must be presented repeatedly.
Visual Evoked Potentials (VEP) check the visual pathways
These allow the measurement of the transmission of nerve impulses through the visual pathway. The visual pathway is stimulated using a checkerboard pattern that changes its black-and-white profile at rapid, regular intervals. The patient observes the pattern on a screen with one eye at a time. The electrical potentials triggered in the visual cortex are recorded by the physician using electrodes attached to the patient’s head.
This measurement method is particularly significant in the diagnosis of inflammatory or circulatory-related changes of the optic nerve and visual pathways (e.g., optic neuritis in multiple sclerosis).
Somatosensory Evoked Potentials (SSEP) check the sensory pathways
SSEPs allow an assessment of the central and peripheral sensory conduction pathways. With SSEPs, the physician can test the transmission of sensory perceptions from the arms and legs via the spinal cord to the brain. This is done by applying repeated short electrical stimuli to the ankles and wrists. The resulting signals are recorded from the head or the spinal canal area.
This method is used, for example, to more precisely detect sensory disturbances (e.g., in multiple sclerosis).
Motor Evoked Potentials (MEP) check the pathways that transmit movement
MEPs examine the conduction of nerve impulses responsible for muscle movement from the brain, via the spinal cord, to the extremities (arms and legs).
During the examination, a strong magnetic field is applied over the patient’s head, neck, or lumbar region, stimulating the corresponding areas of the cerebral cortex or spinal cord. This results in brief, involuntary muscle twitches in the arms or legs, depending on the stimulated brain area. Some patients find these sensations unpleasant, but they are not dangerous (some rare contraindications are known to the physician and should be observed).
The term “evoked potentials” is derived from the Latin word evocare, meaning “to call forth.” The definition of evoked potentials describes a neurological diagnostic method used to test the conductivity and functional capacity of nerve pathways, based on the stimulation of a sensory organ or a peripheral nerve.
The potentials cause so-called potential changes in the cerebral cortex, which can be detected by means of electroencephalography (EEG). In this way, the induced electrical potential can be observed in specific areas of the nervous system. Every sensory stimulus triggers electrical potential changes in the brain, which is why the evoked activity can be measured and displayed with precision.
What are evoked potentials and why are they measured?
The measurement of evoked potentials depends on the type of potential being assessed:
- Visual Evoked Potentials (VEP):
Visual evoked potentials are measured to diagnose and evaluate the optic nerves and the visual pathway. The analysis of visual evoked potentials is useful, among other things, for the diagnosis and monitoring of multiple sclerosis, tumor-like disorders of the central visual pathway, existing optic neuritis or injury, and glaucoma. - Auditory Evoked Potentials (AEP):
The analysis of auditory evoked potentials is used to assess the central and peripheral auditory pathways. AEP is applied in the diagnosis of diseases and tumors of the auditory nerves, in cases of suspected cerebellopontine angle tumors, and for the earliest possible detection of hearing disorders. - Somatosensory Evoked Potentials (SEP):
Somatosensory evoked potentials are examined when sensory disorders are suspected. This enables targeted diagnostics for determining the level of spinal cord lesions, investigation of Huntington’s chorea, and for detecting sensory nerve damage (peripheral or central). With the examination of somatosensory evoked potentials, the cause of sensory disturbances can be interpreted. In this process, the sensory nerve pathways from the hands or feet leading to the brain are measured. - Motor Evoked Potentials (MEP):
Motor evoked potentials are used in a corresponding examination to assess the functional capacity of the motor system. The motor system is responsible for voluntary movements, and in certain diseases this system can be impaired or even damaged. The analysis of motor evoked potentials is used in the diagnosis of central and peripheral nerve disorders such as amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Diseases of the motor cortex and the motor pathways in the spinal cord can be diagnosed through the evaluation of motor evoked potentials. Magnetic evoked potentials are measured using a coil that generates a magnetic field over the head or spine.
Evoked potentials are measured using EEG.
From the Latin evocare (“to call forth”, “to evoke”) and potentia (“strength”, “power”), they are differences in potential in the electroencephalogram (EEG) that are triggered by stimulation of a sensory organ or a peripheral nerve. In a broader sense, all deliberately induced electrical phenomena in the EEG can be understood as evoked potentials. The measurement of evoked potentials is carried out by attaching electrodes to the patient’s head, which record the brain’s electrical activity.
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