Bioelectric source measurements are influenced by the measurement location as well as the conductive properties of the tissues. Volume conductor effects such as the poorly conducting bones or the moderately conducting skin are known to affect the measurement precision and accuracy of the surface electroencephalography (EEG) measurements. This paper investigates the influence of age via skull conductivity upon surface and subdermal bipolar EEG measurement sensitivity conducted on two realistic head models from the Visible Human Project. Subdermal electrodes (a.k.a. subcutaneous electrodes) are implanted on the skull beneath the skin, fat, and muscles. We studied the effect of age upon these two electrode types according to the scalp-to-skull conductivity ratios of 5, 8, 15, and 30 : 1. The effects on the measurement sensitivity were studied by means of the half-sensitivity volume (HSV) and the region of interest sensitivity ratio (ROISR). The results indicate that the subdermal implantation notably enhances the precision and accuracy of EEG measurements by a factor of eight compared to the scalp surface measurements. In summary, the evidence indicates that both surface and subdermal EEG measurements benefit better recordings in terms of precision and accuracy on younger patients. 1. Introduction Clinical electroencephalography (EEG) and evoked potential (EP) recordings such as the visually evoked potentials (VEPs) demand high signal-to-noise ratios (SNRs), minimization of skin artifacts, and high accuracy, to name a few important criteria. Subdermal needle electrodes (a.k.a. subcutaneous needle electrodes) are commonly used in clinical electromyography (EMG), which are inserted into the muscles of interest. It is less commonly known that these subdermal needle electrodes also record continuous EEGs and EPs in intensive care units (ICU) [1–4]. The measurement setup is achieved by inserting the needle nearly tangentially to the skin so that it is stabilized and the recording tip touches the skull. Furthermore, these recordings offer higher SNRs with lower proclivity of standard measurement artifacts when compared with traditional surface measurements and are more suitable for long-term EEG monitoring in the ICU. Higher SNR requires less averaging, thus yielding faster and more accurate diagnostic measurements. We believe that clinical EEGs and EPs such as the VEP could adopt the subdermal measurement setup, thus placing the lead on the skull bypassing the artifact-prone skin. Previously, we correlated skull conductivity with age (Figure 1) [6]. In that
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