Inverse Imaging of Distributed Oscillatory Activity

Abstract

Several types of bioelectric current source produce external electric and magnetic fields with oscillatory characteristics. Often, these sources are not well localized and may be distributed over a wide spatial range or may consist of several simultaneously-active localized sources distributed over a wide area. Additionally, the oscillation associated with such activity may not be synchronized over space — activity in different regions may oscillate at different frequencies. The brain’s alpha rhythm is one such example, with activity spread over a large region of the brain oscillating at a characteristic frequency between 8 and 12 Hz [1]. The basic electrical activity of the gastrointestinal system is another example. Frequencies of oscillation in gastrointestinal electrical activity include a 3 cycle-per-minute (cpm) slow-wave in the stomach and slow-waves that range from 8–12 cpm in the small intestine, with more distal segments of the small bowel typically having lower frequencies than more proximal segments [2],[3]. We present a technique to address the problem of estimating the source current distribution from external measurements of the electrical activity.