How are electrodes placed for somatosensory evoked potentials (SEPs)?

Updated: Feb 26, 2019
  • Author: Sombat Muengtaweepongsa, MD, MSc; Chief Editor: Selim R Benbadis, MD  more...
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Recording electrode sites are identified by anatomical landmarks. Those on the head are defined using the international 10-20 system, or its extension, the 10-10 system. Electrode CP3 is midway between C3 and P3, and electrode CP4 is midway between C4 and P4. CPi denotes either CP3 or CP4, whichever is ipsilateral to the stimulated limb; CPc is the contralateral centroparietal scalp electrode. CPz is midway between Cz and Pz.

Recording electrodes over the spine are placed in the midline and can be labeled with the name of the vertebral body they are placed over followed by the letter S, for example, C5S or T10S.

Recording montages for cortical SEP components are either cephalic bipolar, in which both electrodes are placed over the head, or referential, in which a reference electrode is placed at a noncephalic site. Cephalic bipolar montages yield signals with less noise contamination and are preferred for routine clinical use.

For upper limb SEP studies, electrodes are placed over Erbs point (ie, the angle between the clavicular head of the sternocleidomastoid muscle and the clavicle), both ipsilateral and contralateral to the stimulus (labeled EPi and EPc, respectively). For lower limb SEP studies, IC denotes an electrode placed over an iliac crest.

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