If you say brackets, you mean (), {} or []?
On piano parts, when the bracket reaches from the left-hand part to the right hand part, it can also mean that you play the note with the left hand eventhough it's on the right-hand lines: it's just easier to note the pitch without the extra lines. They often add m.d. (manus dexter = right hand) or m.s. (manus sinister) as well. That or it makes the harmonies easier to follow.
I don't know the music or the score, but ( ) may well mean a ghost note. It's basically a way to fake your way out of impossible intervals or quick note repetitions, but you can use it intentionally as part of your phrasing. On a guitar or bass, you could mute the note and not really make it sound out.
It could be an optional note - like: don't bother if it's too fast for you, just play the ones without the brackets.
