Actually it depends on what kind of mouse you use. Virtually all of the better ones are programmable and you can have them do anything you want, horizontal scrolling included. Mine even has extra buttons completely assignable to any function you want. I have two of them for copy and paste. Very neat, I can copy/paste anything (of course that includes anything you can copy/paste in Cubase) with the same hand that holds the mouse, without even touching the keyboard.