Figure 4.

Individual differences in CS+-evoked lever pressing and DA signaling. Scatterplots show relationship between change in lever press performance during CS+ trials (CS+−pre-CS+ y axis) and each of four measures of DA signaling (x axis): the amplitude (a), area (b), and frequency (c) of DA transients during CS+ trials, and the average change in DA concentration (d) during those trials. Data points (jittered) are for all trials with the CS+ for rats preexposed to saline or cocaine. Lines show regression slopes generated by linear mixed-model analysis, separately plotted for each group and for all rats. See Table 2 for regression coefficients and significance values for individual analyses. (e) Summary of the mediation (path) analysis. The mediated effect of cocaine exposure on reward seeking through DA signaling is the product of two distinct paths: path a is the total effect of cocaine exposure on DA signaling and path b is the direct effect of DA signaling on reward seeking that controls for the effect of cocaine. A bootstrapped estimate of the product of paths a and b, which represents the mediated effect, was significant. Unstandardized coefficients are shown for each path (*p<0.05).