title: Reversal of electrical sign in the occipital area: physiological or montage artifact.
abstract: The cases illustrate situations in which there is a polarity difference between the anterior and posterior regions resulting from the montage rather than actual physiological differences. The major most easily missed problems arise from diffuse slow waves, but a more easily recognized example of reversed or unexpected apparent polarity from a 14 and 6 per second positive spike burst is reviewed. Problems usually occur when waves in question have a wide distribution and provoke larger voltages in input 2 than in input 1 in some channels. The technologist needs to be aware of the potential problems. When they occur, a variety of montages including montages with a reference outside the involved area and possibly a non-cephalic reference can be employed to clarify the situation. A high index of suspicion, astute technologists and suspicious electroencephalographers are necessary to prevent misidentification of these wave forms as physiological in origin.
mesh_terms: D004569:Electroencephalography; D006801:Humans; D009778:Occipital Lobe / Q000502:physiology*