Tone or laser-elicited behavior in the first two sessions. (A) The learning effect demonstrated by tone alone-elicited behavior. The behavioral score was accumulated every 5 successive trials. One-way ANOVA followed by the Dunnett test for multiple comparisons were used to compare the difference of behavioral scores between Session 2 and 1 (* p < 0.05). As can be seen, rats learned to escape immediately after the tone after about 25 tone-laser pairing trials. (B) Laser-induced nociceptive behavior in the first session. (C) The acquisition and extinction of the conditioned response demonstrated by tone alone-elicited behavior. *, *** p < 0.05, p < 0.001, respectively, compared with "Baseline"; ###, p < 0.001, compared with "Trained", one-way ANOVA followed by the Newman-Keuls Multiple Comparison Test. "Baseline" and "Trained" are the averaged behavioral scores in the first and second sessions (trials 1–30 in Session 1 and trials 51–55 in Session 2, see above Fig. 1A), respectively.