2.5. fMRI data preprocessing
Functional data analysis was conducted using the AFNI software package. Preprocessing steps were applied, including the removal of the first three pre-steady state images. The following procedures were performed: despiking, slice timing correction, realignment, transformation to MNI space, and Gaussian FWHM smoothing with a kernel size of 4 mm. To account for potential confounding factors, three polynomial terms and the six motion parameters were regressed out during the analysis. Additionally, TRs with excessive motion were identified and censored based on a criterion defined as the Euclidean norm of the derivative of the six motion parameters exceeding 0.3.The modeling of the neutral and methamphetamine cue blocks was accomplished by convolving the stimulus timing with a 31-second block regressor, resulting in the estimation of one response for each condition before and after stimulation. Notably, the primary analysis did not incorporate separate regressors for box trials or response periods.