^^ I agree that's a part of it.
I'm guessing there's a physical part of the brain, connected with memory (short and long term) that controls interest in something. I'm not really up on my neuroscience, thus the conjecture on the physical part.
A more real question would be if people with Alzheimer's have moments of boredom.
Where does the instinctual urge for new stimuli come from? This obviously isn't consciously happening, or at some speed to be unnoticable.
And personality plays a part (or whatever sum total of experience equates to).
Someone can listen to jazz all day (possibly even the same record) and never become bored, while someone else can perceive within less than ~1 second that immediately they are bored of this music (taste?). Or they listen for a small amount of time and change the music, to a different genre, different song.
I've always wondered in layman's terms how a strong stimulant affects ADD/ADHD types, that it provides more focus/interest. Where say caffeine can provide the opposite experience, anxiety/no attention.