Techniques are described to determine a location of at least one oscillatory signal source in a patient. Processing circuitry may determine expected electrical signal levels based on a hypothetical location of the at least one oscillatory signal source. Processing circuitry may determine the electrical signal levels and determine an error value based on the expected electrical signal levels and the determined electrical signal levels. Processing circuitry may adjust the hypothetical location of the at least one oscillatory signal source until the error value is less than or equal to a threshold value, including the example where the error value is minimized.