The standard two-step scheme for modeling extracellular signals is to first compute the neural membrane currents using multicompartment neuron models (step 1) and next use volume-conductor theory to compute the extracellular potential resulting from these membrane currents (step 2). Here, we present the volume-conductor theory used in step 2. The neural output from step 1 can be represented in terms of (i) a set of point sources, (ii) a set of line sources, (iii) a current-source density, or (iv) one or several current dipoles. We derive equations for the extracellular potential under the approximations (i–iv), discuss the validity and applicability of the different approximations, and explain how they are related. We also discuss how to model the effects that the electrode itself can have on the measured extracellular potential.

An electroencephalogram (EEG) reflects the summation of electrical activity arising from excitatory and inhibitory post-synaptic potentials of pyramidal neurons. EEG electrodes are traditionally placed on the scalp according to the International 10–20 system of electrode placement to reproducibly record cortical electrical activity. There are a number of different montages that may be used to best analyze an EEG, and allow for interpretation of the spatial distribution and localization of the EEG activity across the cortex. Neonates may require a reduced montage. Raw EEG data remain the gold standard of neurophysiological monitoring; however, reduced-montage and quantitative EEG techniques have allowed providers, particularly in the neonatal and pediatric intensive care units, to have supplementary data to interpret, in real time, at the patient’s bedside or via remote access. This chapter reviews the technical aspects of neurophysiological monitoring, including the practice and underlying principles of initiating, recording, displaying, and interpreting EEG. Quantitative trends, including CDSA and aEEG, are included.

Electrode artifacts may have a spiky, periodic or rhythmic appearance. Characteristically, it is limited to the involved electrode with no field. Sweat artifact may involve multiple channels and may be confused with lateral eye movements or GRDA. Eye movement and glossopharyngeal artifact may mimic frontally predominant GRDA. EKG artifact may be confused with periodic discharges. Characteristically, it corresponds to the QRS complexes. Ventilatory artifact may be confused with bursts of cerebral activity. Characteristically, it corresponds to the respiratory rate. Head tremor presents as occipital predominant rhythmic artifact. Maneuvers and devices such as bed-percussion, CRRT, ECMO, CPR and even brushing teeth may lead to ictal appearing rhythmic artifacts.Discharges associated with cortical myoclonus are best appreciated in the central channels as these are relatively free of muscle artifact. Chewing artifact may electrographically mimic a generalized tonic clonic seizure