A medical device comprising: a memory configured to store information indicative of electrical signal levels at or across a plurality of electrodes implanted in tissue of a patient; and processing circuitry configured to: determine the electrical signal levels based on the stored information; determine, based on a hypothetical location of at least one oscillatory signal source, expected electrical signal levels at the plurality of electrodes; determine an error value based on the determined electrical signal levels and the expected electrical signal levels; repeatedly adjust the hypothetical location, and repeatedly determine the error value for each of the adjusted hypothetical locations of the at least one oscillatory signal source until the determined error value is less than or equal to a threshold value, wherein a location of the at least one oscillatory signal source is based on a hypothetical location for the at least one oscillatory signal source for which the determined error value is less than or equal to the threshold value; and generate information indicative of the location of the at least one oscillatory signal source. a memory configured to store information indicative of electrical signal levels at or across a plurality of electrodes implanted in tissue of a patient; and processing circuitry configured to: determine the electrical signal levels based on the stored information; determine, based on a hypothetical location of at least one oscillatory signal source, expected electrical signal levels at the plurality of electrodes; determine an error value based on the determined electrical signal levels and the expected electrical signal levels; repeatedly adjust the hypothetical location, and repeatedly determine the error value for each of the adjusted hypothetical locations of the at least one oscillatory signal source until the determined error value is less than or equal to a threshold value, wherein a location of the at least one oscillatory signal source is based on a hypothetical location for the at least one oscillatory signal source for which the determined error value is less than or equal to the threshold value; and generate information indicative of the location of the at least one oscillatory signal source. determine the electrical signal levels based on the stored information; determine, based on a hypothetical location of at least one oscillatory signal source, expected electrical signal levels at the plurality of electrodes; determine an error value based on the determined electrical signal levels and the expected electrical signal levels; repeatedly adjust the hypothetical location, and repeatedly determine the error value for each of the adjusted hypothetical locations of the at least one oscillatory signal source until the determined error value is less than or equal to a threshold value, wherein a location of the at least one oscillatory signal source is based on a hypothetical location for the at least one oscillatory signal source for which the determined error value is less than or equal to the threshold value; and generate information indicative of the location of the at least one oscillatory signal source.