Figure 1.

Arial configuration (a) and a side profile picture (b) of the self-administration apparatus with conjoined chambers that were separated by a partition. Rats were connected to infusion lines surrounded by a flexible metal sheath and then placed into the neighboring chambers either with a solid black Plexiglas partition in place isolating the rats during the session (Iso; not shown) or with a black Plexiglas partition containing a wire mesh section that allowed for visual and some tactile social cues, and stronger olfactory and auditory social cues during sessions (Soc; shown in b). Each chamber contained a retractable lever (active lever; i.e., reinforced lever) located 2.5 cm from the dividing partition wall and 7.5 cm above the floor. Experiment 4 included the addition of a non-retractable inactive lever (i.e., non-reinforced control lever; not pictured) on the wall opposite the active lever located 2.5 cm from the dividing partition wall and 7.5 cm above the floor. A camera sensitive to low levels of light (Panasonic WV-CP284, color CCTV, Suzhou, China) was used to record self-administration sessions and was mounted 60 cm above the center of the apparatus. A WinTV 350 personal video recorder (Hauppage, NJ, USA) captured live video and encoded it into MPEG streams for later analysis. Later videos were analyzed for entries into the 4 quadrants (Q1-Q4) demarcated by lines drawn on the display.