Fig. 4.

Fifty-kilohertz USVs emitted by Non-Resident and Resident rats during the first 30 min of drug SA for sessions 1–2. a Total number of calls (means ± SEM) for cocaine versus heroin SA. b Scatterplots of calls emitted during cocaine versus heroin SA. Each dot represents a single rat. c Preference score is calculated as the ratio of log-transformed calls emitted during cocaine versus heroin SA. § indicates significant difference (p ≤ 0.05) between cocaine and heroin. * indicates significant difference (p ≤ 0.05) between Residents and Non-Residents. # indicates significant difference (p ≤ 0.05) from 0