Compare and contrast bipolar and referential derivations in the EEG, and give at least three (3) examples of each type of derivation. Include the appropriate filter settings and sensitivities for each

Bipolar versus Referential Derivations
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Polysomnography (PSG) is the “recording of multiple neurophysiologic signals, simultaneously, in reference to the objectives of a clinician” (Friedman, 2014, p. 25). According to Marshall, Robertson, and Carno (2013), there is no type of derivation is recommended because various activities take place simultaneously and require different types of derivation. Two derivations of interest are the bipolar and referential derivations, which will be the topic of concern in this paper, as it seeks to compare and contrast their use in EEG and PSG.
A bipolar derivation is when a pair of electrodes record from an active signal location while in a referential derivation, one electrode is the recording terminal while the one is a reference electrode that is not placed in a location with an active signal (Marshall et al., 2013). The referential recording is commonly used in polysomnography while bipolar recording is used in seizure patients to isolate sharp wave from spike activity. The referential recording is ideal for EEG derivations to aid in sleep staging by employing at least three channels: frontal, central, and occipital channels. The standard derivations are F4-M1, C4-M1, and O2-M1 which are recorded from an opposite hemisphere as F3-M2, C3-M2, and O1-M2 as backup for EEG. Frontal derivations help to enhance the visibility of slow wave activity while central derivations help to make the spindling activity and K-complexes more noticeable and enable occipital derivations to reduce alpha activity.

Ultimately, the activity of all the three channeled derivations helps to identify sleep stages in a better way. Derivations are ordered in montages to allow viewing, and in the case of sleep recording, the table in Appendix 1 shows a montage, whose order is in reference to the AASM.
Bipolar derivations, on the other hand, are used for a chin EMG, which is also required while performing sleep staging as it helps to reduce EMG activity in REM sleep. This process requires the placement of the bipolar derivations’ electrodes on the two muscles of the chin: mentalis and submentalis. A limb EMG, including a leg and sometimes an arm, is often recorded on standard polysomnograms. Respiratory airflow and effort recordings are described as a montage because they appear as a collection of derivations, and they are a form of bipolar recordings that transfer signal from the ancillary equipment via two input electrode jacks. The ancillary equipment, or a built-in oximeter, is used to transmit direct signal for oximetry. Other than the EMG, another example of bipolar derivation is ECG, which entails the use of lead 1, which is negative, and a positive lead 2. Also, left and right anterior tribialis (LAT/RAT) utilize the bipolar derivations.
Bipolar derivations, thereby, are used to measure the difference in ability to transmit between two actives electrodes while the referential electrodes measure the difference between an active and an inactive electrode. Hence, the active electrodes in bipolar derivations overlie a recording site that is electrically active as described earlier in the case of chin or limb EMG recording. Interelectrode distance, therefore, is imperative in determining the effects of these two derivations because a larger interelectrode distance is associated with an elevation of EEG amplitude. Hence, referential derivations are well-suited for electrocerebral activity. In addition to the EEG, referential derivations are also used in EOG, which are measured by “left and right outer canthi (LOC/ROC) while the contralateral mastoid (A1/A2)” is used as a reference to the EEG channels, mainly C3/C4/O1/O2 (Friedman, 2009, p. 25).
Appendix 1

References
Friedman, M. (2009). Sleep apnea and snoring: Surgical and non-surgical therapy. Chicago, IL: Saunders Elsevier. Retrieved on 11 December 2016.
Marshall, B., Robertson, B., Carno, M. (2014). Polysomnography for the sleep technologist: Instrumentation, monitoring, and related procedures. Missouri: Elsevier. Retrieved on 11 December 2016.