Methods for the Localization of Electrical Sources in the Human Brain

Continuous Source Imaging of Scalp Ictal Rhythms in Temporal Lobe Epilepsy

“…Dipole source modeling is one method of estimating the character of cerebral sources underlying a scalp voltage field (16)(17)(18)(19). This mathematical technique attempts to find a theoretical dipole source that can produce a voltage field on a model head that is equivalent to the…”

“…Some investigators have noted a correlation among scalp ictal EEG patterns (e.g., frequency and evolution) and intracranial seizure origins in the temporal lobe (3-6). We believe that, as has been shown for interictal spikes (7-15), source analysis of the voltage fields of scalp ictal rhythms can provide more information concerning seizure origin and propagation than can visual inspection of EEG traces.Dipole source modeling is one method of estimating the character of cerebral sources underlying a scalp voltage field (16)(17)(18)(19). This mathematical technique attempts to find a theoretical dipole source that can produce a voltage field on a model head that is equivalent to the…”

“…Certain nonphysiological assumptions are necessary to apply volume conduction principles, which are the basis of dipole analysis, to human EEG. The brain is usually modeled as a sphere of uniform conducting material, and concentric shells are added around this to imitate the skull and scalp (16)(17)(18). The source of the field is considered to be a pointlike dipole.…”

Anatomical and Physiological Substrates of Event‐Related Potentials

“…Wood (1982) has applied the methods of Sidman er al. (1978) and Darcey et al (1980) to the AEP scalp distribution data shown in FIGURES 1 and 2 above. These models assume a three shell model of the head, with conductivities corresponding to those of the brain, skull and scalp, and calculate the location and orientation of the best-fitting single dipole for a given potential field.…”

“…However, by restricting the shape and homogeneity of the medium and the number and form of the sources, a solution to the inverse problem may be achieved within the limitations of those assumptions using numerical minimization techniques. This approach has been applied to EEG and evoked potential data by a number of investigators (e.g., Schneider, 1972;Henderson, er al., 1975;Kavanagh, er al., 1978;Sidman et al, 1978;Darcey, 1979;Darcey er al., 1980). Such iterative solutions to the inverse problem have typically assumed: (a) that the head can be approximated by a homogeneous, isotropic, spherical conductive medium, consisting of one or more spherical shells of differing conductivity to simulate the brain, skull, and scalp; and (b) that the source of the potential field on the surface of the sphere is either one or two dipole sources.…”