Neuronal processing of conspecific and related calls in the torus semicircularis of Rana r. ridibunda Pall. (Anura): single-unit recordings.

1. Single-unit responses in the torus semicircularis of Rana ridibunda were analyzed with regard to the neuronal mechanisms underlying call identification. Particular attention was directed to the question whether discrimination among the conspecific calls (mating, territorial and release calls), and between these and the mating calls of the related species R. lessonae and of the hybrid R. esculenta, can be explained by differences in the neuronal responses. 2. 75% of the single cells responded to at least one call. 25% of the neurons in this group were selective in the sense that they failed to respond to at least one of the calls. 3. Three of the single cells were selective for one type of call alone, the conspecific mating call in each case. Most of the selective neurons responded to three calls, having a preference either for the conspecific calls or for the amplitude-modulated mating calls. Such responses can be explained by the neurons' operation as either frequency or time filters. 4. Even the neurons that were nonselective, responding in some way to all the calls, differentiated among them with regard to response magnitude; that is, either the territorial and release calls elicited higher discharge rates than the amplitude-modulated mating calls, or the reverse. 69.8% of the single cells exhibited maximal responses to the conspecific mating call. The territorial and release calls elicited maximal responses in only 7.8% of the single cells. 5. In discrimination among the three mating calls, the temporal pattern of the calls plays a role. The differences in pulse-group timing are encoded by the overall response magnitude and not by way of differences in degree of synchronization. 66% of the nonselective neurons responded maximally to one of the three mating calls and very much less intensely to the other two. 6. No correlation was found between the types of call to which the various neurons responded maximally and the CF's of those neurons. Only very few cells represented a frequency and time filter exactly tuned to a particular call.