Figure 1.

Locomotor activity (mean ± SD) in animals after repeated injections of Meth or saline. Only animals from which successful intracellular recordings were subsequently obtained are included here. a, Animals classified as behaviorally sensitized (n = 22) exhibited a stronger and longer-lasting locomotor response to Meth during the test phase compared with the baseline phase. b, Animals classified as nonsensitized (n = 13) exhibited no significant changes in locomotor activity in response to Meth injection from the baseline to the test phase. c, Saline-treated animals (n = 15) exhibited a low level of locomotor activity in response to saline injection during both phases. d, Total activity counts (collapsed across the 2 h behavior period) for each of the three groups. ^*p < 0.001 versus baseline. Error bars indicate SD.