This does not surprise me and shouldn't surprise anybody else. Do you understand what this study says? It simply shows that while listening to audio, the blood flow in the brain has a relationship to the audio rate(amplitude and frequency). OR correlated to it. Was the podcast in stereo? Have you ever had music dance in your head? Stereo speech can do the same. If you look closer, you might even find a directional rate, the matches the podcast. But just the audio rate in sufficient. An enveloped response.
The stimulus has a audio rate, and with stereo a directional rate. Why would not, the response to that stimulus.......have those same rates?
The study simply states the obvious brain response from an audio stimulus.
The only thing new is watching it, recording it and analyzing it. Showing what should be there. It only shows what was listened to.