Figure 3.

SRR conditioned rats learned to breathe more slowly and spent more time breathing below the conditioned RR threshold of 80 breaths/min. Group differences in respiration emerged over the course of 20 sessions. (A) The percentage of samples where RR met criterion (≤80 breaths/min). SRR conditioned rats displayed an increasing incidence of breaths below the target RR (1-factor RM ANOVA), and a greater % of samples under threshold than yoked controls (2-factor RM ANOVA: significant main effect of Group) over training. Multiple comparisons analysis revealed a significantly higher % of samples below threshold in SRR conditioned vs. yoked rats during Sessions 4, 6, 9, 10, 12, 14–17, and 20. (B) SRR conditioned rats decreased their average resting RR by 10.6 breaths/min (1-factor RM ANOVA) and their RR was lower than that of yoked controls (2-factor RM ANOVA: significant main effect of Group) over training. Follow-up testing revealed a significant difference between SRR conditioned and yoked animals in resting RR during Sessions 10, 14–16, and 20; conditioned rat resting RR values were >6 breaths/min lower than yoked control values in all cases. Note in (A) that % of samples under threshold for SRR conditioned rats is by definition % of samples in darkness, whereas for yoked rats the % of samples under SRR threshold did not have a direct relationship with the light being on or off. (C) SRR conditioned and yoked rats spent similar amounts of time resting. Average percentages of each 2 h session spent resting (% resting) for SRR conditioned rats and yoked controls are shown for pre-conditioning and Sessions 1–20. Animals typically spent between 50 and 60% of each trial at rest, with no differences observed between groups over the course of training. This suggests that factors other than differential activity levels were responsible for reducing resting RR in SRR conditioned rats. ^*p < 0.05 SRR conditioned vs. yoked, post-hoc Holm-Sidak comparisons.