For starters, guitarists have the ability to synchronize their brains while playing. In a 2012 study in Berlin, researchers analyzed 12 pairs of guitarists playing the same piece of music; one would lead and the other would harmonize. Researchers were able to produce scans of each of their brains. They discovered that the guitarists’ neural networks would synchronize not only during the piece, but even slightly before playing.
That synchronization occurs in the brain regions associated with music production and social cognition, so it contributes to how tight a band sounds. When people talk about a band’s chemistry, this may well be what they’re seeing. It explains why brothers are the core duo in so many famous rock bands.