Clustering with combined physiological signals

Methods of generating an extended cluster are disclosed. A first cluster including data representative of a first signal indicative of an abnormal physiological symptom is generated. A second signal is detected as representing a second abnormal physiological symptom and the second abnormal physiological symptom continues after the first abnormal physiological symptom ends. An extended cluster including the data from the first signal and the second signal is generated that extends from the time when the first abnormal physiological symptom occurs to the time when the second abnormal physiological symptom ends. The first and the extended cluster may include data of both the first and second signals the entire period of the clusters. If desired, the first signal or the second signal may be provided from a sensor implanted in a patient's brain tissue.