Information Transmission in the Auditory Brainstem Figure 4. Single tone responses of two cat high-sync neurons. Data from two cat VCN neurons shown in a similar fashion to Fig. 2. Stimulus frequency used to evoke data in panels A and B are 400 and 900 Hz, respectively. Firing rates, except for those indicated by the red dashed lines, were measured during the stimulus duration (0–50 ms). Red dashed lines represent onset firing rates evoked by 90-dB tones, except in panel F (70 dB SPL). doi:10.1371/journal.pone.0044286.g004 the 100–1500 Hz frequency range. Therefore, the frequency of the tone that evoked rmax is not necessarily equal to CF. With the exception of three data points, rmax values measured from ANF responses are always ,0.9. Red dots in Fig. 7C represent r values computed from responses to CF tones. Distributions of r values for ANFs and VCN neurons are almost non-overlapping and statistically significant (p,0.01, two-sample Kolmogorov-Smirnov test). Black and red continuous lines in Fig. 7C present average rmax values for cat and chinchilla ANFs, respectively. Entrainment indices as a function of CF computed from responses to CF tones in chinchilla and cat VCN neurons are shown in Figs. 7B and 7D, respectively. VCN neurons in both species can evoke responses that are highly entrained (i.e., entrainment index .0.9). The main difference, however, lies in the CF range of neurons that can yield such responses. In the case of the cat, responses of neurons with CFs up to 1 kHz can show entrainment, which contrasts with the 500–600 Hz upper limit in the chinchilla. It is also evident that entrainment in VCN neurons is larger than in ANFs (dots in Fig. 7D). PLOS ONE | www.plosone.org 8 September 2012 | Volume 7 | Issue 9 | e44286