Fig. 4. Respiratory behavior in freely behaving, yoked and operantly conditioned snails. Pneumostome activity was measured over three 45 min training sessions for (A) freely behaving animals (N=18), (B) yoked animals (N=17) and (C) operantly conditioned animals (N=31). Values are means ± s.e.m. for number of pneumostome openings. Animals operantly conditioned show a significant decrease in pneumostome openings across sessions. The other two treatment groups show no difference in pneumostome openings over the training time course. 1, Training session 1; 2, Training session 2; MT, Memory Test; NS, not significant. ^*P<0.05 compared with performance during Training session 1 within each treatment group.