Hi, the waveband powers of the EEG signal are not as simply interpreted as in the previous answer. There is a lot more going on than simple function or area-like activity attribution. There are several explantions for this, the main one being that frequency powers for a given EEG signal mainly tell us about synchronised neuronal firing in the recorded time period, generated by several areas of the brain (not neccessarily near to the recording site), as they are recorded at the scalp of a participant, so be careful to take into account the context of your recording and research paradigm, as well as other factors (i.e. tiredness, caffeine ingestion, light conditions etc.) that can affect your results. I agree that the time-frequency analysis is better, if your experiment has fixed events that you want to describe, however.

To answer your question, though, the ratios wont tell you anything about synchronicity. You have to use connectivity measures for that, such as PLV, wPLI or some other that depend on the phase of the signal.

Hope this answer helps you somewhat.