Acoustically evoked immediate early gene expression in the pallium of female túngara frogs.

In anurans, much is known about the role of the auditory midbrain in processing conspecific calls, but comparatively little is known about the role of the pallium. To address this deficiency, we investigated the induction of the immediate early gene egr-1 by natural mate chorus in the medial, dorsal, lateral, and ventral pallium of female túngara frogs. We found strong acoustically evoked egr-1 expression in the dorsal medial pallium (p < 0.01) and ventral pallium (p = 0.02), with a weaker effect in the lateral pallium (p = 0.05). In the ventral pallium, acoustically induced egr-1 expression was stronger in the anterior portion. Measures of movement and olfactory activity could not explain a significant portion of acoustically evoked pallial egr-1 expression. In contrast, egr-1 expression in the auditory midbrain covaried with egr-1 expression in the dorsal medial pallium and ventral pallium, suggesting that their activity was coupled with auditory activity. Taken together, these results suggest that the acoustically evoked egr-1 expression in the dorsal medial pallium and ventral pallium were a direct result of auditory stimulation. Furthermore, although both anatomical and electrophysiological evidence demonstrate that multiple modalities overlap in the frog pallium, our results show that a multimodal stimulus is not required to activate pallial neurons. Although the functional role of the frog pallium is not known, our results demonstrate that species-specific sounds activate spatially segregated and anatomically distinct areas of the frog pallium, inviting further investigation into the role of the frog pallium in acoustic communication.