Fig. 6.

CCK_E neurons recorded in vivo have uniform V-shaped FRAs and diverse temporal responses to tones. (A) Examples of light-evoked (Left, 50 ms blue light) and sound-evoked (Right, 100 ms 1.5 kHz pure tone at 70 dB sound pressure level [SPL]) voltage traces from one CCK_E unit. Action potentials from light or sound presentations from the respective experiment are aligned and overlaid (gray traces, 103 light-evoked and 1,106 sound-evoked action potentials); black traces, average waveform). Insets: Example spike train from one stimulus presentation. (Scale bars: 0.3 mV, 50 ms.) (B) Example FRAs from four CCK_E neurons (B1 through 4) and their associated peristimulus time histograms (PSTHs) are shown below each respective FRA. PSTHs were acquired from spike counts (2-ms bin width) at each neuron’s best frequency (BF) stimulation at all sound levels tested. The bar above each PSTH indicates tone duration (100 ms). (C) Measurements of tuning sharpness as a function of frequency. BF and the FRA Q₂₀ values for all recorded units. CCK_E neurons (red) had V-shaped receptive fields. One V-shaped unit was narrower at its tip than others (indicated by a high Q₂₀ value) but had a wide low-frequency tail. The sampling of CCK_E neurons was restricted to low and midfrequency regions of the ICC due to limited light penetration and virus injection location. (D) Measurements of the shape of FRA curves. Q₁₀ is plotted against Q₄₀ for each unit. Symbols below the dashed line indicate a widening of the FRA. All FRAs of CCK_E neurons widened with increasing sound level, which is a reflection of their V-shaped tuning.