Uncovering the Fundamentals of Polarity within the EEG: A Closer Look

A thorough understanding of the governing concepts of polarity behavior within electroencephalograph (EEG) promotes analytical and thus technical proficiency of the technologist by providing a skill set to logically resolve the myriad of waveform presentations that are expected across all montage derivations. In addition to avoiding a reliance on cursory conceptualization techniques, a solid grasp of the underlying theory of EEG polarity permits a fundamental realization of the cause-effect relationships between the various directions of eye movement and the resulting multitude of wave deflection presentations observed across all montages. Such wisdom can logically account for the futility of using a particular bipolar montage to localize discharges of interest that are located at end-of-chain. Further, it provides a logical template from which to make sense of physiological and nonphysiological contamination within referential electrodes. Regardless of montage formatting, an EEG epoch can be deconstructed into discrete components; all of the left-sided electrodes within each pair of leads, or channel, are classified as input 1, whereas the right-sided ones are termed input 2. The Polarity Rule states that if input 1 is more negative with respect to input 2, there will be an upward deflection of the associated wave. All wave deflections within any montage arrangement can be explained from this core rule. For those expected to take examinations that include EEG polarity questions, this deeper appreciation may assist by shifting away from the need to memorize a plethora of scenario-dependent wave behaviors.