Hi. I'm in a neuroscience PhD program studying MRI, so EEG devices (like Muse) are not exactly my area... I'll shift your question slightly.
If I understood, you asked which brain regions are associated with which frequencies. I think this is still a researched area.
However, EEG has pretty poor spatial resolution. If you're trying to target specific regions, it can tell you about left vs right, front vs back, but beyond that it's limited. Given that Muse is just a set of electrodes on the forehead, we might be able to separate left from right, but that's all.
On the upside, the research I've seen has shown that whole-brain frequencies are important. When you're sleepy and you close your eyes, your whole brain (all of the EEG electrodes in the figure of the previous post) enter an alpha frequency. Similarly, I think gamma is associated with a state of focus. I've also heard of left-right frontal gamma asymmetry related to negative or positive thought, depending on the direction of the asymmetry.
So to summarize, research currently associated certain states of mind with certain whole-brain frequencies. With this technology, we can't quite tell what brain regions are responsible.