1. A method for retaining physiologic data in an implantable medical device comprising: (A) receiving a first signal set associated with a physiologic condition; (B) receiving a second signal set; (C) detecting, by the implantable medical device, a possible occurrence of a neurological event based on at least the first signal set; (D) storing in a first data structure comprising memory a data record relating to the second signal set, the data record representing information about the neurological event, the first data structure being an age-based circular buffer wherein older data stored in the first data structure, including the data record, are replaced with new data records as additional data are received; (E) determining a priority index for the data record based on a severity of the neurological event; and (F) transferring the data record from the first data structure for storage in a second data structure comprising memory upon determining that the priority index of the data record is greater than another priority index of another data record in the second data structure, the second data structure distinct from the first data structure.