Don't you have to activate a Brain Control?
If you are meaning the space bar then no, it is a hotkey assigned in your screenset. If its a custom screen it may or may not be set up. Problem with the space bar however is it is a hotkey and like I mentioned above will only work if there is a FeedHold button on the screen you are viewing at the time you press it. For example if you are on MDI and you have just commanded a move but decide you need to feedhold, pressing the space bar will not work, you would have to first change to another page that has a feedhold button on it. If however you were using an external button via an OEM trigger then it would work regardless of whether there was a feedhold button on the screen.
Hood