INTRODUCTION TO EVOKED POTENTIALS

EVOKED POTENTIALS
There are three main types of evoked potentials being used in clinical practice- visual, auditory and somatosensory.

The principle on which these evoked potentials are measured is that brain is the final destination of all the sensations. If we stimulate sensory, auditory or visual pathway, and record tiny electrical potentials so generated in brain by placing electrodes over scalp, we can demonstrate the integrity of these pathways. Further abnormalities suggest various types of diseases.

In its simplest form, visual evoked potential is performed by asking patient to look at TV screen where a visual stimulus is provided (usually one eye at a time) and recording is made by electrodes placed over the occiput.

Auditory evoked potential is recorded by providing (one by one) auditory click stimuli via headphones and responses are recorded by electrodes placed over mastoids.

Somatosensory potentials are recorded by electrically stimulating a peripheral nerve like median or posterior tibial nerves and responses are recorded over scalp (laterally for median and midline for posterior tibial, corresponding to arm and leg areas of homunculus).