We used the log10-ratio of the individual microarray intensities to the average intensities of all samples from the same brain region profiled in the same phase as the primary measure of gene expression. Quality control of gene expression data was performed by principal component analysis using MATLAB R2007a (Mathworks Inc., Natick, MA). Outlier samples (less than 2%) were removed from the data set based on extreme standardized values of the first, second, or third principal components, with absolute z-scores more than 3.
