Rhalena A. Thomas, Michael G. Metzen, and Maurice J. Chacron

Understanding how sensory information is processed by the brain in order to give rise to behavior remains poorly understood in general. Here we investigated the behavioral responses of the weakly electric fish Apteronotus albifrons to stimuli arising from different contexts, by measuring changes in the electric organ discharge (EOD) frequency. Specifically, we focused on envelopes, which can arise either due to movement (i.e., motion envelopes) or because of interactions between the electric fields of three of more fish (i.e., social envelopes). Overall, we found that the animal’s EOD frequency effectively tracked the detailed timecourse of both motion and social envelopes. In general, behavioral sensitivity (i.e., gain) decreased while phase lag increased with increasing envelope and carrier frequency. However, changes in gain and phase lag as a function of changes in carrier frequency were more prominent for motion than for social envelopes in general. Importantly, we compared behavioral responses to motion and social envelopes with similar characteristics. While behavioral sensitivities were similar, we observed an increased response lag for social envelopes primarily for low carrier frequencies. Thus, our results imply that the organism can, based on behavioral responses, distinguish envelope stimuli resulting from movement from those that instead result from social interactions. We discuss the implications of our results for neural coding of envelopes and propose that behavioral responses to motion and social envelopes are mediated by different neural circuits in the brain.

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