What are evoked potentials?
Evoked potential (EP) tests or evoked response tests are a diagnostic tool used to measure the time it takes for the brain to respond to various stimuli from the different senses, including sight, hearing and touch. They can be used to diagnose problems in the nervous system, such as multiple sclerosis.
The nervous system is a complex network of nerve cells threaded throughout our bodies, which send information to and from the brain as electrical impulses. Visual information is sent from the eyes after converting incoming light into an electrical signal; auditory information is sent from the ears; and somatosensory (tactile) information is sent from the skin.
What does an EP consist of?
There are three main types of evoked potentials, which test responses to sight, sound and touch. In all three, electrodes are placed on the scalp to read the brain’s response.
1. Visual evoked response test (REV): the eye is presented with stimuli such as flashes of light or checkered patterns.
2. Auditory brainstem evoked response test (RATE): sounds or tones are used to see if there is a problem with the auditory pathway in the brain or the acoustic nerve, which connects the ear to the brain.
3. Somatosensory evoked response test (SESS): evaluates response times to low-level electrical shocks administered to a part of the body where the nervous system might be involved, for example, if the physician suspects a spinal cord injury.
EPs are used to confirm a diagnosis or to monitor a patient’s nervous system.
Why are evoked potentials done?
EPs are generally used to confirm a diagnosis or monitor a patient’s nervous system. It is often used to corroborate or confirm a diagnosis of multiple sclerosis, as slow response times to stimuli may indicate that the myelin sheath insulating nerve cells is damaged, which is a key symptom of MS.
EPs can also be used to:
- Assess brain activity in comatose patients.
- Test certain nerves, such as the optic nerve, for damage
- Detect lesions and tumors
- Test vision and hearing
- Diagnose and/or monitor conditions that cause nerve damage.
Advances/developments
With the advent of more advanced diagnostic tools, such as MRIs, the use of EPs, although it has decreased somewhat, but they can still be a useful tool to provide extra evidence to make a diagnosis.