Hello. Since these injections are not so precise that they can target only a single structure, we report which structure got the majority of the injection, as well as any other structures that also received some of the injection.
From the “Injection Site Polygon Drawing and Informatics Processing” section of the project overview document available here :
“The structure receiving the largest proportion of signal intensity was distinguished as the primary structure, and all other structures were considered secondary structures. A quantified injection summary is provided for each image series that shows the relative amounts of signal detected within each
infected structure.”