Table 2.

Effect of drug expectation on conditional place preference and locomotor activity. In examining the influence of drug expectation on conditional place preference and locomotor activity, fentanyl administration to demonstrator mice predicted one of three situations for observer mice: fentanyl on the fentanyl-paired side (“Drug”), vehicle on the vehicle-paired side (“No Drug”), or simply an injection whereby fentanyl was given daily to the demonstrator mice (“Daily”). On Test Day, fentanyl was administered to demonstrators of all three observer groups and 10 min later, observers received a vehicle injection in the neutral compartment and were allowed free access to all three chambers

Observer groups	Assay	Train: fentanyl to demonstrators in the home cage	Train: vehicle to demonstrators in the home cage	Test
Daily	Conditional place preference and concomitant locomotion	Predicts fentanyl and vehicle injections on both sides	N.A.: demonstrators receive fentanyl again in home cage	Fentanyl to demonstrators: observers expect an injection
Drug	Conditional place preference and concomitant locomotion	Predicts fentanyl on the fentanyl-paired side	Predicts vehicle on the vehicle-paired side	Fentanyl to demonstrators: observers expect fentanyl on the fentanyl-paired side
No Drug	Conditional place preference and concomitant locomotion	Predicts vehicle on the vehicle-paired side	Predicts fentanyl on the fentanyl-paired side	Fentanyl to demonstrators: observers expect vehicle on the vehicle-paired side