According to the professor, what was unexpected outcome of the PET scan?

Listen to part of a lecture in a Psychology class.
Professor: What I really hope we can achieve today is to learn how music can affect our feelings, really grasping the essence of music. Actually, you already knew music has an influence on human’s feeling in many ways before ever coming to this class. However, I’d like focus on how to do this today. Actually, it’s the thing about humans. Music is universal form and has been so in every human civilization since the beginning of time. It’s like we’re hard-wired to appreciate music.
    Okay, when we hear music, it stimulates some areas of our brain. In addition to this, when we hear a low frequency sound transforming to a high frequency sound, it actually makes our brain react in a certain way. So this is what I want to talk to you about today, a research done on the relationship between music and the brain. This research involved Positron Emission Tomography (or PET) scan. This is a kind of scan that can project three dimensional images of the internal organs, and can even detect and display the areas in the brain that are being stimulated.
    Here’s one experiment that we can explore further. Researchers asked subjects to listen to music, and they used the PET scan to detect what areas in the brain were being stimulated. So you may ask, what did they discover? One region is very obvious, the area of the brain devoted to audio stimulation. I mean, it’s music, right? But, the thing that was really amazing was that another area of the brain lit up. It’s the part that handles visual information. This was definitely something that the researchers had not anticipated. Now, if you think about it, it’s really amazing that the visual area lit up because of audio stimulation. Specifically, the areas that lit up are called Brodmann areas 18 and 19, known as "the mind’s eye." There is a visual cortex in each hemisphere of the brain. The left hemisphere visual cortex receives signals from the right visual field and vice versa. These areas like a mental canvas. So when you listen to music, your mind tries to symbolize an image to go well with that sound. These two areas are in the outer layers of the cerebral cortex.
    All right, another remarkable outcome of the experiment was that music even activated not only the cerebral cortex but also areas deep in the brain. They are called "the limbic system." The limbic system is a deep primal area of the brain that has to do with memory and emotion. And if you think about it, that makes sense, too. I mean, even myself, when I listen to a song that I loved as a child, I’m instantly transported back to the feelings that I had at that time. In a similar way, if you listen to fast, upbeat music, you’ll tend to feel a little happier. Therefore, music is closely connected to both visual images and emotions. So people have tried to make good sounds, or music, since ancient times.
    Okay, now let’s take a look at how people made sounds, I mean music. Apparently, music has been important to people since a very, very long time ago. In fact, the oldest known instrument, a type of flute, is dated to be 30 to 40 thousand years old. That predates agriculture. Was music more important than food? Well, let’s explore further. 31 broken pieces of a mammoth tusk were found in Germany by a team of archaeologists. After they put the pieces together, the completed instrument was 11cm long and had three finger holes in it. It looks like a modern-day flute. Experts have concluded that it was capable of producing a very broad range of complex sounds.
    Now, let’s talk about the flute in more detail... I mean, about making it. lt would take such a long time to obtain a mammoth tusk, hollow it out, cut it perfectly in half, and drill holes into it. Then, putting the two halves back together again and making an airtight seal, oh, and that would have been done with stone tools. Can you imagine the amount of time that must have taken? You really have to marvel at the amount of work that it must have involved. Okay, so it’s obvious that music must have been important. But why? Why was music important?
    Well, some researchers have argued that music is JUST something that tickles certain areas of our brain, but I think music is much more than that. First, in ancient civilizations, hunters, for example, could have sung and danced together to coordinate attack strategies during combats. Urn, there is one more example. In those ancient societies, when mothers carrying babies would go out and look for berries, the mother would have to put her baby down to gather them, right? Well, the mother could have sung to the baby to let the baby know she was still there. As a result, music connected people then and still does now. This is also true with modern music, including rock and roll, the blues, jazz, and hip-hop.