What we do (clinical neurophysiology)

We use EEGs to measure your brain activity to help us identify any irregular or abnormal activity in relation to some clinical events which may have occurred to you over a period. We carry these tests out on a variety of ages (neonates to adults). For information for children please see our children's page.

EEGs are generally performed to help diagnose patients with epilepsy. In our department we perform different types of EEGs to help with a diagnosis, such as routine, sleep deprived and ambulatory. In some complexes cases and/or surgical pathways we performed long-term (3-5 day) EEGs, called video-telemetry. This can be done in the hospital or at home. You can find our patient information sheets for the different types of EEG we perform below.

The brain works by a series of nerve impulses, which cause electrical signals within the brain. When a part of the body is stimulated, for instance, the eyes by a flashing light, or the ears by a clicking sound, the brain responds to this stimulation. This response is called an ‘evoked potential’.

The electrical signals within the brain (also called brainwaves) can be recorded through the scalp. The brain’s responses to those are often very small but can be recorded using special techniques.

Types of evoked potentials

There are various types of evoked potentials, each with a different method of stimulation:

• Visual evoked potential (VEP) tests look at the pathway from the optic nerve to the part of the brain where images are interpreted and turned into pictures.
• Brainstem auditory evoked potential (BAEP) tests look at the pathway from the ear to the part of brain that interprets sound.
• Somatosensory evoked potential (SSEP) tests look at the pathway from the peripheral nerves in the arms and legs to the sensory part of the brain.

Usually, we repeat each stimulus a number of times so that plenty of responses are recorded. The computer then averages these out to show how the nerve pathways are working.

We use nerve conduction studies to test the electrical conduction of impulses travelling along your nerves. To measure this, a special recording electrode is placed onto your skin (usually on your hand, arm or leg) and then another electrode is used to stimulate the skin. The stimulator produces small electrical pulses which feel like a sharp tapping sensation. We repeat the process for a number of different nerves. There are no side effects, although you might find it uncomfortable. We usually use this method to examine nerves in your arms or legs.

If the nerve is trapped, damaged or diseased then the signals will be altered.

An appointment will usually last between 30 minutes and an hour, depending on your problem and the extent of testing needed.

Find out more, including how to prepare for your study, in our nerve conduction studies patient information guide, which can be found at the bottom of this page.

Pacemaker or implanted cardiac defibrillator

Please let us know if you have a cardiac pacemaker or an implanted cardiac defibrillator by calling our department - see contact us.

In addition to nerve conduction studies, your doctor might perform another test to record the electrical activity of your muscles.

Electromyography (EMG) involves inserting a small needle into the muscle, to view and listen to the electrical activity generated within the muscle. You might be asked to move in a certain way to contact the muscle being tested.

The test uses a small needle, so shouldn't be too uncomfortable. You might have some minor bruising and feel a little sore for a short time after the test.

The activity we record can provide information not only about the muscle but also about the nerve that supplies it and the neuromuscular junction between the two. Depending on your symptoms and a doctor's examination, we might use EMG to test one muscle or several.

Anticoagulants

Please let us know if you're taking warfarin or might have a problem with bleeding or clotting, as there's a risk that the needle might cause problematic bleeding into the muscle.

Find out more, including how to prepare for your study, in our nerve conduction studies patient information guide, which you can find below.