Figure 1.

(A) Schematic overview of the behavioral protocols used in the pilots, the maternal deprivation experiment and the complex housing experiment. PR, progressive ratio. (B) Three different configurations in the liberation task were tested: (1) Escape To Box 1 in which the partner was trapped in the cylinder and could be liberated from the cylinder into box 1 (the test rat compartment), (2) Escape To Box 2 in which the partner was trapped in the cylinder and could be liberated into box 2, and (3) Not Trapped configuration in which the partner was situated in box 2 and lever presses of the test rat opened both doors. (C) Liberation task set-up: two operant chambers are connected through a removable cylinder. The cylinder can be closed on both sides by automated mechanical doors made of transparent Plexiglas with holes that allowed rats to see, smell and hear, but not touch each other.