The "double-collar" technique for EEG electrode preparation and placement.

For accurate and reliable EEG recording, electrode resistances must be kept relatively low and constant. To ensure that these conditions are met, a fixing agent, collodian, is usually used to fix the electrodes 6rmly to the scalp. Collodian, however, produces m y unwanted side effects. A “double-collar” method of electrode placement is described whereby electrodes may be fumly fixed to the scalp without the use of collodian. This technique is both faster and less troublesome than the use of collodiaa. Using this technique, electrode resistances at vertex and occiput were well below generally acceptable criteria (averaging under 5000 ohms) and there was no significant increase in resistance at either placement following nearly 2 brs of continuous EEG recordings. It is concluded that, under certain laboratory conditions, the “double-coUar” method of electrode preparation and placement is superior to the use of collodian. DESCRIPTORS: EEG, Electrode placement. Increased use of Averaged Evoked Response techniques in the psychophysiology laboratory makes it essential that reliable, relatively noisefree electrophysiological recordings be obtained. In electroencephalographic (EEG) recordings the use of high amplification of the signal necessitates low and constant electrode resistances in order to prevent unwanted noise from appearing in the record. Electrodes must be firmly attached to the scalp in order to ensure this low and relatively constant resistance at the electrode sites. Collodian, a fast drying fixative, is used in most laboratories to fix electrodes to the scalp. While collodian acts as an excelIent fixing agent there are a number of negative side effects from its use: 1) With collodian, application of electrodes is a lengthy procedure. 2) Subjects will report that the smell of the collodian is unpleasant and reminds them of a hospital. 3) During its application the Research done under support from NIMH Grant tMH-19560 awarded to Dr. L. Erlenmeyer-Kimling (New York State Psychiatric Institute) and from the Department of Mental Hygiene of the State of New York. The authors wish to express their appreciation to Dr. L. Erlenmeyer-Kimling and Dr. B. Tursky for their valuable suggestions and encouragement in the preparation of this paper. Address requests for reprints to: George Fein, Department of Medical Genetics, New York State Psychiatric Institute, 722 W. 168th Street, New York, N.Y. 10032. collodian will sometimes drip or run on unwantet areas of the subject’s scalp and hair. 4) If thf collodian should get entangled in the subject’! hair, removal of the electrode can produce somt discomfort. 5 ) This discomfort during removal ma) be alleviated by using acetone, which may itself b experienced as a noxious stimulus by some sub jects. That is to say, the abrasive action of thc acetone may further irritate a scalp which has already been cleaned with acetone (during applica. tion of the electrodes) and has had an electrode fixed to it for a period of time. 6) With repeated use 01 collodian some subjects have complained of an inereased dryness and flaking of the scalp. These side effects are greater for subjects with long hau and can present real difficulties for the experimentel as well as the subject. Description of the Technique For the past 6 months we have used a technique ir our laboratory which allows the EEG electrodes tc be adequately fixed to the scalp without the use 01 collodian. The EEG was recorded between vertea and left ear and occiput and left ear. The occipital lead was 2 cm above the inion along the midline. Before applying the EEG electrodes, a part is made in the subject’s hair along the midline. (Bobby pins are used to keep hair in place.) The area of ScdF selected for the placement of the electrode is then 480 vigorously rubbed with a Q-tip ma UntiI the scalp under the electrode si8 pink. The EEG electrodes are prep2 A small Beckman adhesive collar small Beckman skin potential elech center hole of the collar is directly 0’ the electrode. Enough Beckman elc then applied so that the cavity is backing of the small collar is then n adhesive backing exposed. A large sive collar is then placed face dov collar so that the center hole of thc directly over the electrode. Both I “trimmed” by cutting vertically alc the electrode. The paper backing 01 is then removed exposing the secon The electrode is then applied to the scalp and the vertical strips of rem collar are pressed down along 1 subject’s hair. The preparation ani the electrode is illustrated in the phc I . If the adhesive collars have Fix. 1. Sequence of electrode prep ment using the “double-collar” techni The small adhesive collar is in place ani collar and paper backing is ready I electrode. Top row right: Both colla] dotted tines are drawn on the paper t collar to indicate where both collars shi row left: Both collars are in place (the smaller), the paper backing of the la. removed and both collars have beel right: The electrode is fitted to the sc