Figure 2. Non-reinforced lever responding behavior.

A) 1^st 10 min of self-administration. Only limited + yoked rats exhibited high levels of non-reinforced cocaine responding on days 14, 15, 18, and 19 during the first 10 minutes of cocaine self-administration. B) 1^st 1 hour of self-administration. All cocaine-access groups showed an initial non-reinforced active-lever responding for the first 1 hour of self-administration during cocaine acquisition on day 4. C) Inactive lever responses over entire day. There were no differences in the inactive lever responses within or between groups across all days.