In addition to stimulated dopamine release, we also measured the frequency of naturally occurring phasic dopamine release events, i.e., dopamine ‘transients’ prior to the start of each behavioral session (Wightman et al., 2007; Aragona et al., 2008). Interestingly, significantly more dopamine transients per minute were observed in the core (2.4 ± 0.19) than shell (1.5 ± 0.15; t61 = 4.053, p < 0.001). However, there were no significant differences in the frequency of transients observed in nonphasic versus phasic cell locations in either the core (2.0 ± 0.24 versus 2.7 ± 0.26; t31 = 2.008, p > 0.05) or shell (1.3 ± 0.19 versus 1.6 ± 0.18; t28 = 0.93, p > 0.05).
