DECREMENTS IN AUDITORY RESPONSES TO A REPEATED CONSPECIFIC SONG ARE LONG-LASTING AND REQUIRE 2 PERIODS OF PROTEIN-SYNTHESIS IN THE SONGBIRDFOREBRAIN

Earlier work showed that playbacks of con-specific song induce express ion of the immediate early gene ZENK in the caudo-medial neostriatum ( NCM) of awake male zebra finches and that this response disappears wit h repeated presentations of the same stimulus. In the present study, w e investigated whether repetitions of a song stimulus also elicited a decrement in the electrophysiological responses in the NCM neurons of these birds. Multiunit auditory responses in NCM were initially vigoro us, but their amplitude decreased (habituated) rapidly to repealed sti mulation, declining to about 40% of the initial response during the fi rst 50 iterations. A similar time course of chance was seen at the sin gle unit level. This habituation occurred specifically for each song p resented but did not occur when pure tones were used as a stimulus. Ha bituation to conspecific, but not heterospecific, song was retained fo r 20 h or longer. Injections of inhibitors of protein or RNA synthesis at the recording site did not affect the initial habituation to a nov el stimulus, but these drugs blocked the long-term habitual:ion when i njected at 0.5-3 h and at 5.5-7 h after the first exposure to the stim ulus. Thus, at least two waves of gene inducl:ion appear to be necessa ry for long-lasting habituation to a particular song.