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Neurophysiology
A guide for patients and carers
What are evoked potentials?
An EEG shows the complex electrical activity of the brain that is going on from minute to minute throughout life. The responses of the brain to an individual stimulus - a sound, a touch, a flash of light - are usually buried amongst the general background activity of the brain and cannot easily be picked out.
Evoked potentials are electrical responses produced in the nervous system by stimulation of some kind. Clinical neurophysiology is most commonly concerned with stimulation of one of the senses - usually vision, hearing or the sensory nerves in the limbs.
A single evoked potential resulting from one stimulus is normally quite small and difficult or impossible to distinguish from the background EEG activity. However, if the evoked responses to many stimuli, rather than just one, are collected and averaged the signal emerges clearly. All the electrical activity not directly related to the stimulus is ‘averaged out’ and disappears from the recording, allowing the response caused by the stimulus itself to be seen quite easily.
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Contents
- Introduction
- What is clinical neurophysiology?
- Who works in a neurophysiology department?
- What will happen in the clinical neurophysiology department?
- What is an EEG?
- Why is my doctor sending me for a sleep EEG?
- Can an EEG be carried on yound children and babies?
- What will the EEG show in someone with epilepsy?
- What is an ambulatory EEG?
- When is video-telemetry used?
- Can the EEG help with the decision about possible surgery for epilepsy?
- What are evoked potentials?
- What is evoked potential testing used for?
- What can I expect during the test?
- What is EMG and nerve conduction studies?
- EMG in measuring electrical activity of the muscles
- Summary
- Other organisations that may be able to help
