Sure, the fact that the downloadable log2 intensity expression values included in the Allen database were absolute values, and therefore always positive, was what i hypothesized as well in the end. But having gone back to the site since my first post, the question still remains regarding why, although positive for the above reason, when it comes to the lowest absolute values amongst them, meaning the ones that are considered to be down-expressed or less expressed if we will, in a specific brain area compared to the other one, they are never inferior to 1.4 or 1.3 or 1.2 for example. Why can’t we see values that vary between 0 and 1? They still would be positive. And more importantly, as a consequence, the fold change, which represents a relative ratio of gene expression between two different areas , never ends up being inferior to 1 as well, while we know that it could vary between 0 and 1 for down-expressed genes and between 1 and infinity for up-regulated ones. If it is equal to 1, structure A (in terms of log2 expression) and structure B will be equal with each other. If fc >1, then A>B. But what we may be missing is option number 3 and therefore what happens when B>A.