Figure 4. The 4 phenotypic traits considered as factors of vulnerability to addiction-like behavior.

A. Impulsivity measured by the non-reinforced active responses not paired with a stimulus light during the time-out periods (10 s) after each pellet delivery. B. Cognitive flexibility measured by the reversal test. The reversal test is an FR5 self-administration session, but the active and the inactive levers are reversed compared to the previous self-administration session. C. Appetitive associative learning measured by the cue-induced food-seeking test. The cue-induced food-seeking test is a self-administration session that longs 90 min and is divided into two periods: 60 min + 30 min. In the first 60 min period, all lever-presses are not reinforced (active and inactive lever-presses have no scheduled consequences). In the subsequent 30 min, the white cue light, associated with pellet delivery during a normal self-administration session, is illuminated contingently for 30 min according to an FR5. D. Aversive associative learning measured by the shock-induced suppression test.