a, Experimental timeline. SA, self-administration. b, Training: the number of infusions (each paired with a 5-s light cue) during training are shown (means ± s.e.m.). Cocaine (0.5 mg kg−1 per infusion) supported self-administration, as indicated by high nose-poking in the active hole. Responding in the inactive hole was very low (not shown). c, Drug-seeking tests: shown are the number (means and s.e.m.) of nose-pokes in the previously active hole (a measure of cocaine-seeking) and inactive hole during a 30-min test performed under extinction conditions (nose-pokes deliver cue but not cocaine). Cocaine-seeking increased on withdrawal day 45 (withdrawal day × hole interaction: F1,12 = 14.9, P < 0.01) (n = 7 per group). Asterisk, significantly different (P < 0.05) from withdrawal day 1.