Differences between mothers and virgins were particularly enhanced for tone frequencies falling in the natural pup call range.
(A1 and B1) Comparison of 60–80 kHz (upper panels) and 30–40 kHz (lower panels) tone-evoked LFP phase precision trajectories, averaged only across lateral band LFPs. The magnitude of phase precisions was higher for the latter frequencies since lateral band sites should be more responsive to them. No significant differences between mothers and virgins were found for call-excited sites for either tonal stimulus. However, mothers and virgins did differ significantly at call-inhibited sites for both tonal stimuli. Excited Nmothers=7, Nvirgins=5. Inhibited Nmothers=7, Nvirgins=6.
(A2 and B2) Group comparison of tone-evoked LFP phase precision rise times. Bars depict the mean and standard error of the rise times for each group. No significant differences between mothers and virgins were found for call-excited sites, regardless of the frequency of tonal stimulation (60–80 kHz Mann-Whitney, U=13, Nmothers=7, Nvirgins=5, p>0.05, 2-tailed; 30–40 kHz: Mann-Whitney, U=14, Nmothers=7, Nvirgins=5, p>0.05, 2-tailed). The same was true for call-inhibited sites (60–80 kHz: Mann-Whitney, U=14, Nmothers=7, Nvirgins=6, p>0.05, 2-tailed; 30–40 kHz: t-test, t=0.78, df=11, p>0.05, 2-tailed).
(C) Frequency-dependence of tone-evoked LFP phase precision enhancement in mothers compared to virgins for call-excited (blue) and -inhibited (red) sites. Each point pooled trials from 5 logarithmically-spaced tone frequencies centered on that point. Population-averaged phase precision trajectories were computed separately for call-excited and -inhibited SU sites from each animal group. The average difference (solid lines) between trajectories (mother – virgin) over the duration of the tone quantified the precision enhancement relative to virgins. Shaded bands represent 95% confidence intervals computed by bootstrapping across sites. We found a significant increase only for LFPs at call-inhibited SU sites, with the greatest differences for frequencies falling in the natural pup call range (dashed vertical lines). A smaller but still significant difference was also apparent for tone frequencies above ~30 kHz.