Somatosensory evoked potential (SEP) tests are often used to detect problems during surgeries that might impact your brain, spinal cord, or nervous system. But that’s not all.

Evoked potential tests are used to examine the strength and speed of electrical activity in your body. They measure the electrical impulses traveling to and through your central nervous system in response to a stimulus.

Somatosensory evoked potential tests are sometimes abbreviated “SEP” or “SSEP.” They’re also called somatosensory evoked response (SER or SSER) tests. All of these names and abbreviations refer to the same test.

Other types of evoked potential tests include:

Let’s take a closer look at how SEP tests work, why you might need one, and what to expect.

Other evoked potential tests measure electrical activity between your eyes and your brain, or your ears and your brain. What distinguishes SEP tests is that they monitor the electrical pathways from your limbs all the way to your brain.

Electrodes can be placed on your arms, legs, or both. These electrodes provide very mild electrical stimulation. When the cells in your skin, muscles, and nerves detect this stimulation, they pass that information to your brain.

Another set of electrodes will be attached to your scalp, spine, or both. These electrodes don’t provide any electrical stimulation. Instead, they measure the intensity — called amplitude — of the signal traveling from your nerves to your brain. They also measure if there’s a delay — called latency — in the signal.

SEP tests are most commonly used during surgeries that might impact your brain, spinal cord, or nervous system. By measuring electrical activity during the surgery, doctors can avoid causing damage that wouldn’t otherwise be apparent until after the surgery was over.

SEP tests can also be used to help diagnose neurological conditions like multiple sclerosis (MS). In these cases, SEP tests are usually just one of many tests performed to help gather information and narrow down the number of possible causes of your symptoms.

SEP tests can be used to help diagnose conditions that affect your nervous system. If you have symptoms like uncoordinated movement, poor balance, or muscle weakness, an SEP test is one tool that could help pinpoint the cause.

For example, tumors on or near your spine could affect your body’s ability to transmit signals from your limbs to your brain. In this case, an SEP test could help provide information about the location of the problem.

It’s also common during some surgeries to have an SEP test at the same time. In these instances, you won’t be awake for the test, but they can alert the surgical team if your nervous system is negatively affected by the procedure.

Some surgeries that could incorporate an SEP test include:

Before your test

Before you have an SEP test, be sure to ask your doctor how to prepare. In most cases, you won’t need to fast or stop taking medications, but this may not be true for everyone.

If you have hair, you’ll want to wash it the night before your test so the electrodes can easily be placed on your scalp. Avoid using hair spray, gel, or other styling products.

During your test

You’ll be asked to sit in a chair or lie down on a table. You may need to wear a hospital gown so doctors can access your arms, legs, and back.

A medical professional will place electrodes on your scalp and spine, as well as your arms, legs, or joints. The electrodes will be attached with an adhesive.

The electrodes on your limbs will administer mild electrical impulses. You might feel some discomfort, but it shouldn’t be painful.

The test typically lasts between 1 and 2 hours.

After your test

The SEP test provides immediate results. The doctor might be able to share the results with you right away. Sometimes your SEP test will be one of many tests, so the results might not be meaningful until all tests have been completed.

If the test wasn’t performed by the referring doctor, the results will be sent to them. Your doctor will share the results with you after they’ve had a chance to review them.

SEP tests are considered very safe and do not pose a significant health risk. Be sure to speak with your doctor about any specific concerns you might have prior to your test.

The results of an SEP test show which pathways in your nervous system are functioning properly and which are experiencing disruptions. Your doctor can use this information to help determine the source of your symptoms.

An SEP test alone doesn’t usually lead to a diagnosis, but it often helps to rule out some conditions.

If you’re expecting to have an SEP test done, you may have some questions. Be sure you ask your doctor in advance how to prepare and what to expect from the results.

How long does a SEP test take?

If your SEP test is done as part of a surgical procedure, it will likely last the duration of the surgery. In this case, you’ll likely be unconscious throughout.

If you’re completing an SEP test by itself, you can expect it to take anywhere from 1 to 2 hours.

Why is a SEP test performed?

SEP tests are used during some surgeries to provide doctors with feedback about potential nerve impairments throughout the procedure. This helps them to avoid permanent damage.

You might also need a SEP test if your doctor is trying to diagnose or monitor the progression of a neurological condition. SEP tests can help locate the source of problems with proprioception, or your sense of how your body is oriented in space.

Does a SEP test hurt?

No, SEP tests are not painful. The electrical impulses can cause a tingling sensation that might cause some mild discomfort. SEP tests rarely cause some mild skin irritation.

SEP tests are used to measure how well your nervous system passes messages from your limbs to your brain. It can be used to help diagnose neurological issues or conditions affecting your nervous system.

SEP tests are used during some surgeries as a way for doctors to avoid damaging your nervous system while you’re unable to describe what you’re feeling.

It’s a safe and minimally invasive test, and results are usually available quickly.