Hi @CelineCammarata,
We get asked these types of questions quite frequently. In short, there is no way to download only a subset of the data. You have to download the entire data set and subset it yourself (both for genes, and for brain regions). There are several posts about this data set, but I’d recommend starting here: Gene expression matrix.cvs is too large to load it - #17 by jeremyinseattle.
An alternative approach would be to use the Transcriptomics Explorer to view the data on-line. First, the Sampling Strategy visualization could show you which clusters contain cells from VISa and VISrl (or at least which cells are from VIS but not VISp… there are no regions defined as VISa or VISrl in the online visualization).
Next you could view your genes of interest, and see which clusters they were expressed in. In this example, I added a few random genes, but you could instead add the ones you care about.
Hopefully this is enough to get you started.
Best,
Jeremy