Recording and Interpreting Event-Related Potentials
West Haven V.A. Hospital
I was asked to explain how one records brain electrical activity through the scalp and how one interprets the data.
To place things in historical perspective, I would point out that the recording of the electrical activity of the brain is similar in principle to the phrenologists' endeavor, "bumpologists," as they were called by the English caricaturists (Fig. 1.1). The bumpologists had a perfectly sound idea. They believed that there is localization of function in the brain. In the late 1700s and early 1800s this was a radical notion. Gall and his followers tried to convince everybody that there were mental faculties that could be studied objectively ( Gall, 1810). The original bumpologists assumed that they could assess two features of mental faculties by these objective measures: the location of bumps and the height of the bumps. That is exactly what we do when we measure electrical bumps; we call it the location (or topography) and amplitude of the bump. We make the same assumptions that the phrenologists made: The bigger the bump, the more of this activity or function or mental faculty is occurring. Thus, in Fig. 1.2, the bumpologist on the right has concluded that bumps "No. 3 and 4 are very clear." (These are the very words an audiologist might use when discussing the Jewett bumps, as the records of brainstem activity are familiarly called.) For the phrenologist in Fig. 1.2, bumps No. 3 and 4 refer to influence and conceit and are slight parodies of the mental faculties that Gall and Spurtzheim worked out. Of course we don't use terms like those any more. We call Jewett's bumps 3 and 4 "activity in the superior olivary complex" and "activity in the