Partner preference apparatus. The left panel is a photograph of a typical partner preference session. The choice rat was allowed to move freely between the cocaine-treated and saline-treated partner during a 10-minute test session. When on a given side, each choice rat had full visual, auditory, and olfactory contact with the partner, as well as limited tactile contact. The right panel is a schematic of the chamber used to collect partner preference data. The chamber was custom designed (60 × 54 cm) and was functionally divided into two sides by a solid partition that extends 46 cm into the center of the chamber. In the first analysis, the compartment was divided into two equal halves and time spent on each side was determined (note shaded regions in schematic indicating two sides). In the second analysis, the compartment was divided into three equal areas (two areas in close proximity to each social partner and a third “neutral” area on the opposite side of the chamber) and the time spent in each area was determined (note dotted line in schematic delineating three equal areas).