Figure 7. Relationship between chirp production and 5-HT response. A, Pie chart depicting the proportion of trials that showed chirp and/or 5-HT responses (nfish = 8, ntrials = 131). 5-HT release was observed equally frequently together with chirp production as without chirp production (39% vs. 43%). Trials without 5-HT release occurred equally often with chirps as without (8% vs. 10%). B, Chirp latency and 5-HT response latency calculated relative to stimulus onset. The first chirp was equally likely to happen before or after 5-HT threshold crossing. The blue diagonal line depicts the unity line. Inset shows the PDF of the delays observed between 5-HT threshold crossing and the first chirp on a trial-by-trial basis (nfish = 8, ntrials = 51). Positive delays correspond to the first chirp occurring before the 5-HT threshold crossing. The mean of the distribution was not significantly different from zero. C, There was a small positive correlation between AUC and |Df| in trials in which the fish chirped (red asterisks, ρ = 0.25, p = 0.04, nfish = 8, ntrials = 64), but not in those in which the fish did not chirp (black circles, ρ = −0.007, p = 0.95, nfish = 8, ntrials = 67). Red line, Linear fit to the AUC of chirp trials: slope = 0.036 s2, intercept = 1.24 s, R
2 = 0.06). Black line, Linear fit to the AUC of no-chirp trials: slope = −0.0009 s2, intercept = 3.62 s, R
2 = 4.5 × 10−5). D, We observed a small, but significant correlation between the number of chirps produced and the AUC of the 5-HT current for stimuli with a |Df| of <20 Hz (red asterisks, ρ = −0.34, p = 0.02, nfish = 8, ntrials = 47), but not for stimuli with a |Df| of ≥20 Hz (black circles, ρ = 0.12, p = 0.27, nfish = 7, ntrials = 84). Red line, Linear fit to the AUC of trials with a |Df| of <20 Hz: slope = −4.37 s, intercept = 3.63 s, R
2 = 0.12). Black line, Linear fit to AUC of no-chirp trials: slope = 1.87 s, intercept = 3.41 s, R
2 = 0.014).