To determine how locomotor behaviors are modified by previous ethanol exposure, we developed 2 measures that allow quantitative assessment of locomotor activity levels, and we performed an ethanol dose–response in the rapid tolerance paradigm (Fig. 1B to D). For the hyperactive phase, we determined the area under the curve from 2 to 25 minutes of ethanol exposure, termed the distance traveled (Dist) for simplicity. The difference in Dist between exposures (ΔDist) provided an index of the locomotor alterations elicited by repeated ethanol exposures. Naive flies showed a dose-dependent decrease in hyperactivity as ethanol concentrations increased (Wolf et al., 2002), which was reflected in a decrease in Dist (Fig. 1E). We also observed dose-dependent effects on ΔDist with increased ΔDist at higher ethanol concentrations (Fig. 1F). At 47% ethanol vapor, we observed a small increase in Dist during exposure 2 relative to exposure 1 (Fig. 1B and E). Because the increase in locomotor activity appeared to be limited to hyperactivity onset at 47% ethanol vapor (but not at higher concentrations; Fig. 1B), we determined the time of PS during the first
