We have applied the differential display (DD) technique (1 ) to isolate genes whose expression is regulated in the brain of songbirds when they hear song of their own species. Song is known to cause a marked increase in mRNA levels of two immediate early genes,ZENKand c-jun, in the auditory forebrain of songbirds, the most pronounced induction occurring in the caudomedial neo-striatum, or NCM (2 –4 ). Several studies suggest that this gene regulatory event may be related to song processing, discrimination, and the formation of song auditory memories. For example,ZENKinduction in NCM is highest for songs of the same species, lower for songs of other species, and lowest or absent for nonsong auditory stimuli (2 ).ZENKinduction habituates to repeated presentations of the same song, but can be re-elicited by a novel song (5 ). Similarly, the electrophysiological response of NCM neurons habituates when the same song is presented repeatedly, but is high again when a novel song is then presented (6 ); this song-specific electrophysiological habituation is long-lasting and its long-term maintenance depends on local protein and RNA synthesis (6 ). Finally, behavioral studies indicate thatZENKinduction in NCM correlates with associative learning when song is used as a stimulus (7 ). The studies above suggest that a cascade of gene regulatory events triggered by song in NCM is involved in the formation of song auditory memories.
