Figure 3.

Auditory efferent neurons are not adapted to transmit PRR/frequency information. A, Event-triggered average of single AE neuron activity (black trace is average of responses, shown in gray) aligned to first nerve spike and corresponding fictive grunt reveals time-locked, low-amplitude oscillations (indicated by vertical lines) in AE neuron relative to individual nerve spikes (repetition rate of spikes determines natural call) (Chagnaud et al., 2012). Lower right inset, Strong relationship between duration of fictive grunt and duration of AE response (n = 6 neurons, separate sample from Fig. 2B; different symbols represent different neurons). Multiple symbols represent different trials. Black line indicates linear regression. B, Superimposed intracellular records (color-coded for clarity) of AE neuron activity in response to electrical pulses (artifact indicated by arrowheads) applied in vocal midbrain. Top traces, Repetitive electrical stimulation leads to EPSP summation that depends on stimulation frequency/PRR (higher PRR leads to larger amplitudes as indicated by the difference in membrane potential dV). Bottom traces, Number of electrical pulses applied to vocal midbrain areas (2 vs 3) also leads to differential increases in membrane potential resulting in increased dV. EPSP summation occurs at frequencies (<60 Hz) below the PRR of midshipman fish vocalizations (Bass and McKibben, 2003). Stimulation frequencies are indicated (color-coded).