Timeline of experimental procedures. After one week of baseline recording of feeding, drinking, and activity, two groups of rats (1 and 2) underwent two weeks of forced methamphetamine consumption, while two groups (3 and 4) received water only. This was followed by a two-week abstinence period, during which 4 discrete phase shifts of the light:dark cycle were administered to half of the methamphetamine pre-exposed and not pre-exposed rats (groups 1 and 3) while the other half (groups 3 and 4) remained on the original light:dark cycle. All groups underwent two-bottle choice testing for two weeks following abstinence.