What is Clinical Neurophysiology?

The electroencephalogram (EEG)

The electroencephalogram is a recording of the electrical activity of the brain. Electroencephalography is the process of recording the electroencephalogram. Both are abbreviated to EEG. This test is often referred to as measuring the brain waves or brain activity in the popular press.

The electromyogram (EMG) and Nerve Conduction Studies (NCS)

The term EMG is used in two slightly separate ways.

Firstly it is a category of test, which includes true EMG and nerve conduction studies. These two are often used together in the same patient. In this sense, EMG is used to distinguish these studies from EEG and EP which are performed for quite different types of illness.

Secondly, the electromyogram is a recording of the electrical activity of muscles. Electromyography is the process of recording the electromyogram. Both are abbreviated to EMG. Usually this is performed with a special EMG needle, which is quite small compared to most medical needles. EMG provides information about the muscles themselves and the nerves which drive them.

Nerve conduction studies are studies of the nerves. Small electrical pulses are used to stimulate the nerves and recordings are made of the responses. Felt pads or stick-on contacts are used to connect to the skin in most cases.

Many people find these tests peculiar and sometimes uncomfortable, but they are not usually too painful.

Evoked Potentials (EPs)

Evoked potentials are studies in which the brain's response to stimulation of the senses is recorded. The recordings are made over the scalp in a similar way to EEG, but with only a few connections. These studies include

Visual Evoked Potentials (VEP)
The patient is shown patterns or flashing lights
Auditory Evoked Potentials(AEP)
Clicks are played through headphones. These are sometimes called Brainstem Evoked Potentials.
Somatosensory Evoked Potentials (SSEP or SEP).
Small electrical pulses like those used in nerve conduction studies are applied to the arms and legs.