Part 2 book “Brain source localization using EEG signal analysis” has contents: EEG inverse problem III - Subspace-based techniques, EEG inverse problem IV- Bayesian techniques, EEG inverse problem V - Results and comparison, future directions for EEG source localization. | chapter seven EEG inverse problem III Subspace-based techniques Introduction Over the past few decades, a variety of techniques have been developed for brain source localization using noninvasive measurements of brain activities, such as EEG and magnetoencephalography (MEG). Brain source localization uses measurements of the voltage potential or magnetic field at various locations on the scalp and then estimates the current sources inside the brain that best fit these data using different estimators. The earliest efforts to quantify the locations of the active EEG sources in the brain occurred more than 50 years ago when researchers began to relate their electrophysiological knowledge about the brain to the basic principles of volume currents in a conductive medium [1–3]. The basic principle is that an active current source in a finite conductive medium produces volume currents throughout the medium, which lead to potential differences on its surface. Given the special structure of the pyramidal cells in the cortical area, if enough of these cells are in synchrony, volume currents large enough to produce measurable potential differences on the scalp will be generated. The process of calculating scalp potentials from current sources inside the brain is generally called the forward problem. If the locations of the current sources in the brain are known and the conductive properties of the tissues within the volume of the head are also known, the potentials on the scalp can be calculated from the electromagnetic field principles. Conversely, the process of estimating the locations of the sources of the EEG from measurements of the scalp potentials is called the inverse problem. Source localization is an inverse problem, where a unique relationship between the scalp-recorded EEG and neural sources may not exist. Therefore, different source models have been investigated. However, it is well established that neural activity can be modeled using equivalent current dipole
