American Clinical Neurophysiology Society Guideline 2: Guidelines for Standard Electrode Position Nomenclature 2016 PDF

GUIDELINE American Clinical Neurophysiology Society Guideline 2: Guidelines for Standard Electrode Position Nomenclature Jayant N. Acharya,* Abeer Hani,† Janna Cheek,‡ Partha Thirumala,§ and Tammy N. Tsuchidak¶# * Department of Neurology, Penn State University Hershey Medical Center, Hershey,...

GUIDELINE American Clinical Neurophysiology Society Guideline 2: Guidelines for Standard Electrode Position Nomenclature Jayant N. Acharya,* Abeer Hani,† Janna Cheek,‡ Partha Thirumala,§ and Tammy N. Tsuchidak¶# * Department of Neurology, Penn State University Hershey Medical Center, Hershey, PA, U.S.A.; †Department of Pediatrics and Internal Medicine, Division of Neurology, Gilbert and Rose-Marie Chagoury School of Medicine Lebanese American University, Byblos, Lebanon; ‡NeuroLinks Group, LLC, Tulsa, OK, U.S.A.; § Department of Neurological Surgery and Neurology, University of Pittsburgh Medical Center, Pittsburgh, PA, U.S.A.; Departments of kNeurology and ¶ Pediatrics, George Washington University School of Medicine and Health Sciences, Washington, DC, U.S.A.; and #Division of Neurophysiology, Epilepsy and Critical Care in Center for Neuroscience and Behavioral Health, Children’s National Health System, Washington, DC, U.S.A. Summary: This revision to the EEG Guidelines is an update addition, situations in which AF1/2, AF5/6, PO1/2 and PO5/6 incorporating current electroencephalography technology and electrode positions may be utilized for EEG recording are practice and was previously published as Guideline 5. While discussed. the 10-10 system of electrode position nomenclature has Key Words: Electroencephalography electrode position, 10-10 been accepted internationally for almost two decades, it has System, International 10-20 system, Adult, Pediatric. not been used universally. The reasons for this and clinical scenarios when the 10-10 system provides additional localizing information are discussed in this revision. In (J Clin Neurophysiol 2016;33: 308–311) T he 10-20 system of electrode placement, proposed by the International Federation of Societies for Electroencepha- lography and Clinical Neurophysiology in 1958,1 has been the desirable characteristics, which allows for an extension of the 10-20 system to designate the 10% electrode positions. This extension is designated the 10-10 system. The guideline also international standard for recording routine scalp EEG for discusses the clinical context for the use of the 10-20 and 10-10 clinical use. This system provides a consistent and replicable systems. method of recording EEG with 21 electrodes placed at relative This report is divided into the following sections: (1) distances (10% or 20%) between the cranial landmarks over desirable characteristics of an alphanumeric nomenclature; (2) the head. It has also been used as a standard relative head head diagram of the “modified combinatorial nomenclature”; (3) surface–based positioning method for recording evoked and explanation of the modification of the 10-20 nomenclature within event-related potentials and for various transcranial brain the modified combinatorial 10-10 system; (4) explanation of the mapping methods. deviation from a strict combinatorial nomenclature in the The development of multichannel EEG hardware systems modified system; (5) extension of combinatorial nomenclature and topographic source localization methods has resulted in to positions inferior to those demonstrated in Fig. 1; (6) clinical the availability and frequent use of higher EEG electrode context for use of the two systems. Use of EEG electrode density with improved spatial resolution. Therefore, a modi- position nomenclature for purposes other than clinical EEG, as fication, termed the 10-10 system, was proposed and accepted well as the proposed 10-5 system will not be discussed further in as a standard by the American Clinical Neurophysiology this study. Society2 and the International Federation of Clinical Neuro- physiology.3 This provided nomenclature guidelines for several additional electrodes in the anteroposterior, coronal, and inferior planes. I. DESIRABLE CHARACTERISTICS OF AN With the availability of EEG systems capable of record- ALPHANUMERIC NOMENCLATURE ing with a greater number of channels (e.g., 128, 256), there is a need to standardize the placement of additional electrodes. 1. The alphabetical part should consist of one but no more than two letters. A further extension of the 10-10 system, called the 10-5 2. The letters should be derived from names of underlying lobes system, has been proposed,4 but not been accepted by the of the brain or other anatomic landmarks. American Clinical Neurophysiology Society or the Interna- tional Federation of Clinical Neurophysiology. 3. The complete alphanumeric term should serve as a system of coordinates, locating the designated electrode according to the This guideline describes the method for combining a slight following rules. modification of the International 10-20 system with a slight modification of the combinatorial rule, described below in the a. Each letter should appear on only one coronal line. (In standard 10-20 terminology, the only outstanding exception to Address correspondence and reprint requests to Jayant N. Acharya, MD, DM, this rule are the “T” (temporal) names that appear on both the Department of Neurology, Penn State University Hershey Medical Center, 30 central and parietal coronal lines. For reasons discussed in the Hope Drive, EC037 Hershey, PA 17033, U.S.A.; e-mail: [email protected]. Explanation of the modification of the 10-20 nomenclature Copyright Ó 2016 by the American Clinical Neurophysiology Society ISSN: 0736-0258/16/3304-0308 within the modified combinatorial system section, this excep- DOI 10.1097/WNP.0000000000000316 tion is replaced by a more consistent terminology within the 308 Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 clinicalneurophys.com  Guideline for Electrode Position Nomenclature J. N. Acharya, et al. same letter(s) lie on the same coronal line. Thus, the alphanu- meric nomenclature for each electrode specifies its coordinate location within the 10-20 grid system. Once this is done, the positions 10% inferior to the standard frontotemporal electrodes are easily designated as F9/Fl0, T9/Tl0, and P9/P10. As indicated above, the straightforward designation of an electrode’s coordinate localization by its nomenclature requires replacement of the inconsistent T3/4 by T7/8, which is a readily understandable modification. A more radical modification replaces T5/6 by P7/8. However, even with this more radical departure, P can be recognized as representing parietal when it is associated with a postscripted number with a value of 6 or less, whereas it can be recognized as implying posterior temporal if P is associated with a number with a value of 7 or greater. However, even though T7/8 and P7/8 in the head diagram emphasize the internally consistent logic of the system, it would clearly be an acceptable alternative to continue to use T3/4 and T5/6 without detracting from the logic of the remaining system. FIG. 1. Modified combinatorial nomenclature for the 10-10 system. nomenclature. For emphasis, this modification is displayed on IV. EXPLANATION OF THE DEVIATION FROM A the head diagram in the Head diagram of the 10-10 system STRICT COMBINATORIAL NOMENCLATURE IN THE section with white lettering on a black background.) MODIFIED SYSTEM PROPOSED HEREIN b. Each number should designate a sagittal line so the same The 10-20 system does not name electrode positions postscripted number identifies all positions lying on that forming the four 10% intermediate coronal lines lying sagittal line. (Again, the only outstanding exception to this between the five standard coronal lines containing currently rule in the current 10-20 system is in the “T” numbering. For named electrode positions. The strict combinatorial system example, this results in the F7, T3, and T5 designations all designates the currently unnamed positions by combining the appearing on a single sagittal line. This exception is also names or letters for the two standard electrode positions that eliminated within the recommended nomenclature. Once more surround a currently undesignated 10% intermediate electrode for emphasis, this modification is displayed in the head position. diagram in Fig. 1 with white lettering on a black background.) Thus, positions in the second intermediate coronal line are designated as either the frontotemporal positions (FT) or the frontocentral positions (FC), depending on their location as noted in the head diagram. II. HEAD DIAGRAM OF THE 10-10 SYSTEM The electrode positions in the third intermediate coronal line In Fig. 1, the modifications of the current 10-20 terminol- are designated as temporal-posterior temporal (TP) or centropar- ogy, instituted for reasons explained in the next section, are ietal (CP) as noted in Fig. 1. emphasized by displaying them with white lettering on a black The positions in the fourth and final intermediate coronal background. line are designated as posterior temporo-occipital (PO) or parieto-occipital (PO). The only proposed deviation from the strict combinatorial rule discussed above is in naming the first intermediate transverse III. EXPLANATION OF THE MODIFICATION OF THE positions as anterior frontal (AF) electrodes rather than frontopolar- 10-20 NOMENCLATURE WITHIN THE MODIFIED frontal electrodes. The latter terminology would designate the COMBINATORIAL SYSTEM electrodes with either three letters (FpF) or the same two letters The modified 10-10 terminology replaces the inconsistent (FF). Since neither of these letter designations is desirable (the first T3/T4 and T5/T6 terms with the consistent T7/T8 and P7/P8. The because it uses three letters and the second because it uses the same head diagram in Fig. 1 emphasizes consistency of the terms letter twice), the Committee proposed using the readily understand- T7/T8 and P7/P8 by showing them with white lettering on black able anterior frontal (AF) designation displayed in Fig. 1. circles. The value of this becomes evident when inspecting the Once the above letters are assigned to the currently unnamed head diagram, which shows that, except for Fpl/Fp2 and O1/O2, 10% intermediate positions, then their alphanumeric designation all electrode positions along the same sagittal line have the same is completed by postscripting the letters assigned to an electrode postscripted number and that all electrodes designated by the by the number designating the sagittal line on which the electrode clinicalneurophys.com Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 309  J. N. Acharya, et al. Guideline for Electrode Position Nomenclature lies. For example, in Fig. 1, AF3, FC3, CP3, and PO3 all lie on nomenclature (the letter should indicate the underlying lobe of the the same sagittal line designated by the number 3. brain). It should be emphasized to trainees that P represents parietal As noted in Fig. 1, only one electrode position is placed when it is associated with a postscripted number with a value of 6 between AFz and AF7 (AF3) and between AFz and AF8 (AF4). or less and implies posterior temporal if P is associated with Similarly, there is only one electrode between POz and PO7 a number with a value of 7 or greater. Also, EEG machine vendors (PO3) and between POz and PO8 (PO4). Because of the short would need to change the labeling of electrodes in headboxes. anatomic distance between the two points, placing additional Nevertheless, the additional electrodes included in the 10-10 electrodes (such as AF1/2, AF5/6, PO1/2, PO5/6), would result system can be very useful in certain clinical situations. During in excessive crowding and may be clinically impractical. long-term video-EEG studies of patients undergoing presurgical However, they could be used in patients with large head sizes evaluation, they can provide more precise localizing information if clinically feasible and necessary. with regard to interictal epileptiform discharges and ictal EEG When this is done, each new alphanumeric designation is onsets. In patients with suspected temporal lobe epilepsy, the not only directly related to a slight modification of the 10-20 limitations of the 10-20 system for precise localization have been terminology but also serves as an internally consistent coordinate recognized for several decades, leading to the use of additional system that locates each newly designated electrode position at noninvasive (T1/T2 electrode positions proposed by Silverman) the intersection of a specified coronal (identified by the prefixed and semi-invasive electrodes (nasopharyngeal, sphenoidal). Use letter) and sagittal (identified by the postfixed number) line. of the temporal electrode positions described in the 10-10 system (FT7/FT8, FT9/FT10, T9/T10) can be particularly helpful in such patients and may obviate the need for T1/T2 electrodes. Despite being measured in different ways, the positions of FT9/FT10 V. EXTENSION OF THE 10-10 COMBINATORIAL electrodes closely approximate those of T1/T2 electrodes. NOMENCLATURE TO POSITIONS INFERIOR TO Although some controversy persists, several studies have sug- THOSE DEMONSTRATED IN FIGURE 1 gested that anterior temporal electrodes detect interictal and ictal Positions posterior to electrodes displayed in the ninth and epileptiform abnormalities virtually as well as do sphenoidal tenth rows would be designated as PO9 (10% inferior to PO7), electrodes. They also provide more consistent recording infor- PO10 (10% inferior to PO8), O9 (10% inferior to O1), and O10 mation, do not result in pain and discomfort for patients and do (10% inferior to O2). Electrodes 10% inferior to the ninth row not require physician expertise.5 Nasopharyngeal leads provide would be designated with the postscripted number 11 (F11, less information, are uncomfortable for patients, and are prone to FT11, T11, TPl1, P11, PO11, and O11), and those 10% inferior artifacts and therefore should be avoided for routine clinical use.6 to the tenth row would be designated with a postscripted number Similarly, in patients with mesial frontal lobe epilepsy, some of 12 (F12, FT12, T12, TPl2, P12, and O12). the electrodes from the 10-10 system (FC1/FC2, FCz, C1/C2, CP1/CP2, and CPz) in addition to the 10-20 system may be helpful to best delineate the epileptic focus. Other electrode positions could be used selectively in other types of focal VI. CLINICAL CONTEXT epilepsies as well, but the entire set of electrodes described in The additional, more closely spaced electrodes in the 10-10 the 10-10 system may not always be necessary even for system clearly provide better spatial resolution, but there are presurgical video-EEG monitoring. some practical concerns with its routine use for all EEGs. Using all of the.70 electrode positions described in the Placement of several additional electrodes requires increased 10-10 system, and even additional electrode positions, is likely to time and effort on the part of technologists, potentially reducing be of greatest value when advanced digital studies, such as the number of studies that can be performed in a day. Additional source localization and electrical source imaging, are performed electrodes need to be purchased. Routine EEGs are ordered or in addition to standard visual analysis of the EEG. recorded for a variety of indications, and it is not clear whether the extra electrodes provide clinically meaningful additional information in situations where localization of an epileptiform abnormality is not critical (for instance, in patients with RECOMMENDATIONS encephalopathy or other generalized abnormalities). Also, most Although the decision regarding use of appropriate electrode vendors of commercial EEG machines in the United States positions should be individualized depending on the clinical need continue to provide headboxes with electrode positions and in a given patient, taking all of the factors discussed above into nomenclature limited to the 10-20 system. A commitment from consideration, a reasonable clinical approach would be as follows: the vendors to switch to the 10-10 system would be necessary to promote universal use of the 10-10 system for all EEG studies. 1. For routine EEGs, where the indication is not epilepsy or The change in nomenclature from T3/T4 and T5/T6 to T7/T8 localization of an epileptic focus is not critical, the 10-20 and P7/P8 is essentially a conceptual one. However, one does not system may be clinically adequate for most patients and intuitively think of P7/P8 electrodes as overlying the temporal efficient in terms of time, effort, and cost. It may also be region rather than the parietal region. Although this is consistent sufficient for many diagnostic (such as distinguishing between with the logic proposed in the 10-10 system, it appears to be epileptic and psychogenic events) long-term ambulatory and contrary to one of the desirable characteristics of an alphanumeric inpatient video-EEG monitoring studies. 310 Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 clinicalneurophys.com  Guideline for Electrode Position Nomenclature J. N. Acharya, et al. 2. Because of its greater spatial resolution, the 10-10 system on an assessment of current scientific and clinical information. It provides better localizing information and should be used in is not intended to include all possible proper methods of care for patients undergoing presurgical evaluation in the epilepsy a particular problem or all legitimate criteria for choosing to use monitoring unit. However, not all of the electrode positions a specific procedure. Neither is it intended to exclude any need be used; selective electrode positions can be chosen reasonable alternative methodologies. ACNS recognizes that based on the suspected location of the epileptic focus. specific patient care decisions are the prerogative of the patient Additional electrodes from the 10-10 system may also be and the physician caring for the patient, based on all of the used sometimes during routine EEGs, when an attempt is circumstances involved. The clinical context section is made made to localize the epileptic focus in patients with suspected available to place the evidence-based guidelines into perspective focal epilepsy, and during certain diagnostic ambulatory and with current practice habits and challenges. Formal practice video-EEG studies (for instance, in patients with psychogenic recommendations are not intended to replace clinical judgment. events versus frontal lobe seizures). 3. The entire set of 10-10 electrode positions, with or without additional electrodes, can be used if additional digital analysis, including source localization and electrical source REFERENCES imaging, is planned. 4. Although it would be desirable to switch to T7/T8 and P7/P8 1. Jasper HH. The 10-20 electrode system of the International Federation. for both clinical and educational (including publication) Electroencephalogr Clin Neurophysiol 1958;10:367–380. 2. American Electroencephalographic Society. 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