Figure 3.

Variation in delay sensitivity among FM-FM neurons in the mustached bat's IC. A. Schematic delay function for FM-FM neuron with only facilitatory responses to combinations of tones in the FM₁ and higher harmonic FM frequency bands. The facilitation is tuned to short delays (3 ms best delay) between low-frequency and subsequent high-frequency signals. B. Delay function for FM-FM neuron with both facilitatory and inhibitory responses to combinations. The inhibitory interaction is strongest at 0 ms delay, while the facilitatory interaction is strongest at a longer delay (10 ms). C. Delay function for FM-FM neuron with only an inhibitory influence of signals in FM₁ frequency band. Inhibition is strongest at 0 ms delay. D. Best delays of facilitation for FM-FM neurons and other combination-sensitive neurons (including FM-CF, CF/CF, and non-sonar combinations) from the mustached bat's IC. The FM-FM neurons have distinctly different delay tuning. Dashed vertical line indicates approximate separation between facilitated FM-FM neurons without inhibition (having short best delays) and facilitated neurons with inhibition (having long best delays). Data from Leroy and Wenstrup, 2000; Nataraj and Wenstrup, 2005; and Portfors and Wenstrup, 1999. E. Best delays of inhibition for FM-FM neurons that show no facilitation (illustrated in C) and those that also show facilitation (illustrated in B). For both groups, inhibition is strongest at 0 ms delay. Mechanistic studies suggest that inhibition in both groups has a common origin (see Section III). Data from Nataraj and Wenstrup, 2005; Portfors and Wenstrup, 1999. F. Width of delay tuning (50% Delay Width) in FM-FM neurons from IC is weakly correlated with best delay. Data from Nataraj and Wenstrup, 2005; Portfors and Wenstrup, 1999.