Dendritic mechanisms of auditory stream segregation in an insect.

Abstract

Auditory stream segregation (AudSS) is the process of grouping the auditory scene into coherent perceptual objects. We recently described AudSS in an insect: In Neoconocephalus katydids, a first-order auditory interneuron (TN-1) segregates bat cries with slow pulse rates from conspecific communication signals with fast pulse rates. This insect system provides a powerful opportunity to study neuronal mechanisms of AudSS in an identified neuron with testable behavioral function. TN-1 adapts rapidly to fast pulse rates and responses are completely suppressed. However, if a slow pulse rate of sufficiently different carrier frequency is presented simultaneously, TN-1 responds reliably to the slow rate pulses. The suppression of the fast pulse rate on TN-1, i.e., the critical component of AudSS, is caused by two dendritic processes intrinsic to TN-1. The first mechanism is transient and likely calcium mediated, while the second mechanism is sustained throughout the stimulation and likely sodium mediated. TN-1 responses to slow pulse rates, occurred when the slow and fast pulse rate were transmitted by different groups of receptor cells, which project onto different regions of the TN-1 dendrite. Based on these results, we propose a mechanism of dynamic dendritic compartmentalization to underlie AudSS in the katydid TN-1.