Figure 4.

Cue presentation evokes phasic surges in dopamine and reflects a learned association. Increases in signal (mean + SEM represented by solid and dashed black lines, respectively) were evoked by cue presentation (denoted by black triangle) for operant responding rats (n = 5; top trace). The robust increase in signal was confirmed to be a rise in dopamine concentration by examination of the averaged cyclic voltammogram taken at the peak of the signal (inset). Cue presentation failed to elicit an increase in dopamine in rats (n = 3; bottom trace) that did not have the cue-sucrose pairing. The decrease in signal just after cue presentation was not caused by a change in dopamine. This was confirmed by comparison of the averaged cyclic voltammogram (inset) with the averaged cyclic voltammogram taken from pre-session, electrically evoked dopamine release (r² < 0.01). The signal in operant responding rats was significantly higher than control rats immediately after cue presentation (0.5-2.4 sec; p < 0.05; post hoc Student's t test with Bonferroni correction).