Female stimuli trigger gene expression in male pigeons.

The immediate early gene zenk encodes transcriptional regulators and is believed to be one of the first steps in the formation of long-term memories associated with a given stimulus. In this study, we investigated the expression of ZENK protein product in brain regions that are likely involved in the processing of social stimuli, such as a potential mate. Male pigeons (Columba livia) were exposed to one of the following: (1) a live female pigeon, (2) a video playback of a female pigeon, (3) a video playback of a female cockatoo, or (4) an empty stimulus chamber. The brains were then processed immunohistochemically using an antibody against ZENK protein. When the stimulus was a live pigeon compared to all other stimuli, there were more numerous and more darkly-stained ZENK-positive cells in three "association" regions of the telencephalon: the hyperpallium apicale, the lateral portion of the intermediate nidopallium, and the medial nidopallium. There were no significant differences among the video-playback stimuli. The results suggest that the level of ZENK expression in these "association" regions was influenced not only by the visual presence of a potential mate, but by the presence of non-visual signals, the quality of the image, and the real-time interaction with the stimulus.