Did you look at Enirchr publication ? (Explained in supplementary data here)

Allen Brain Atlas application programming interface (API) to download normalized gene expression values for 20,000 genes measured in 2,500 distinct brain regions. We filtered the data matrix to remove genes and brain regions with more than 5% missing values, imputed the remaining missing values, and log2-transformed all values. We then standardized the values for each gene to obtain scores indicating the significance of up- or down-regulation of each gene relative to its median. Finally, we created gene set libraries with brain regions labeling the 300 most up- or down-regulated genes relative to their median expression in the brain.