Unilateral exposure of 21-day-old mice to doorbell sound induces unilateral seizure susceptibility to subsequent sound. However, this unilateral component of sound-induced seizures, as well as the inhibitory effect of repetitious sound, appear only in these older mice as susceptibility to audiosensitization is declining. Unilateralîty and audiosensitization have separate ontogenetic patterns, and thus involve separate mechanisms. Ether anesthesia eliminates the inhibitory effect of repetitious sound.