Here is what the course built, in the order it built it.
The pitch of a note is a conclusion your brain draws from a repeating pattern of harmonics. The frequency that matches it doesn't even have to be in the sound.
From a scanner's distance, music shares a neighborhood with speech. Up close, some populations seem to answer almost only to music, and one to singing. A stroke can take music and spare language, or the reverse.
A wrong note is mostly a long shot, by odds your brain picked up from the music you grew up with. The ear's own share is smaller than it feels.
A chill marks a moment when the reward system that handles food and money answers those bets, and part of it starts work early. Changing dopamine changed how much people enjoyed music, and what they'd pay for it.
The beat is partly something you supply. The leading explanation, still unproven, is that your brain's movement system keeps it. It runs a little ahead of the beat, even while you sit still.
Practice redraws the brain's maps where the work lands, and an early start probably counts for something.
Lessons make children better at music. The famous gap in IQ is mostly about who takes lessons.
Where music helps a damaged brain, it helps a little, mostly through the beat, and mostly while people practice.
The course began with two students and Barber's Adagio. The same notes reached both. What differed was in the listeners. Each had brought a piece that reliably gave them chills. Parts of the reward system rose as those chills grew stronger. Much of music happens in you.
Plenty is still open. Whether dopamine is the pleasure itself, or only the wanting, is disputed. So is which animals can keep a beat, and how much an early start matters. Several famous findings shrank when someone checked them, among them the Mozart effect and the imagined waltz in the brainwaves. What survived is smaller than the first reports.