Statistical Analysis
The sample size and animal numbers were determined by power analysis of
pre-existing data (Belujon and Grace, 2014; Chang and Grace, 2014;
Belujon et al., 2016; Salin et al., 2021).
Data were analyzed with the statistical program GraphPad Prism (Version
8.0.1; GraphPad Prism, RRID:SCR_002798).
All the results are expressed as the mean ± SEM. A Grubb’s test was used
to identify statistical outliers’ animal. There was no outlier in this
study. The level of probability (P ), for determining groups’
differences, was set at P < 0.05. We followed
significant main effects and interactions (P < 0.05)
with post hoc tests (Sidak’s multicomparison test) which were conducted
only if the F values in the analyses achieved the appropriate
level of statistical significance and the statistical measures of
homogeneity of variance were not significant.
For active/inactive responses in yoked saline animals, a two-way
repeated measure (RM) ANOVA was performed with session as the
within-subject factor and number of nose-pokes as the between-subject
factor. Since corresponding data for cocaine animals did not pass
normality test, a mixed-effects model was used. For incubation of
cocaine craving, a paired Mann Whitney’s test was performed.
Electrophysiological data were analyzed using either a two-way ANOVA
with time (WD1-3 and WD26-45) and drug (saline and cocaine) as factors
followed by Sidak’s post-hoc when comparing more than two experimental
conditions. When comparing two groups, first a Kolmogorov-Smirnov
normality test was used. If data passed the normality test, a unpaired
t-test was used; otherwise, an unpaired Mann Whitney’s test was used.
Complete statistical analyses and exact P values are reported in Table
S1.