Electric shock was delivered via a Grass S88 Stimulator (Grass Technologies, West Warwick, RI) to a small cylindrical copper grid 2 cm in height and 2.5 cm in diameter placed at the opening of the test vial from which the odor previously associated with ethanol or sucrose flowed. Electric shocks were applied every 50 msec for 1 sec each throughout the test. The % flies willing to overcome shock was measured by calculating percent of flies within each vial that walked over shock to obtain the ethanol- or sucrose-associated odor. The percentage of flies from one reciprocal pair of vials was averaged for each N=1.
