Provided are a knockout mouse, a method for screening a substance for suppressing mesial temporal lobe epilepsy, and a method for selecting a technique for suppressing mesial temporal lobe epilepsy. A knockout mouse 30 or more days of age that has lost the function of the Girdin gene in at least the nervous tissues and exhibits the phenotypes of (1), (2), and (3) below. (1) hippocampal sclerosis should be present, (2) extrahippocampal brain damage should be limited, and (3) spontaneous epilepsy that can be said to be of hippocampal origin should be present.