Specializations of bat auditory cortex for processing echoes arriving at different delays

The bat auditory system follows the standard mammalian plan, but many specializations have been uncovered that appear uniquely tailored to support echolocation. However, it still remains uncertain which, if any, neurophysiological specializations are truly unique to echolocation. The question is important because it defines the extent to which bats may serve as general models of auditory processing, and it points towards which elements are critical for biosonar processing. One of their most unique neurophysiological features is the presence of neurons sensitive to the time delay between the outgoing pulse and returning echo. These delay-tuned neurons are found in the auditory cortex of all bats, but their neuroanatomical distribution is distinctly different in FM-type bats compared to CF-type and neotropical fruit bats. In FM bats, delay-tuned neurons are sprinkled throughout primary auditory cortex rather than comprising their own auditory subfield, suggesting they might do more than just target ranging. We hypothesized that delay-tuned neurons might dynamically modulate the neural substrate to match changing pulse acoustics for targets at different distances. Results supported the hypothesis by showing that activation of delay-tuned neurons was directly correlated with concomitant changes in the frequency tuning properties of nearby neighboring neurons.