trigger animation on mouseover of a segment only

If you want only a portion of an image, then create an invisible button or other object that you can assign a ROLL_OVER/ROLL_OUT event listener to.  The event handler can just tell the animation to play() assuming it is a timeline animation.

To play a timeline animation in reverse you can use an ENTER_FRAME event listener and a prevFrame() command.  Each time before you execute the prevFrame command you check if the animation has reached its first frame, and when it does you remove the ENTER_FRAME event listener.

areaName.addEventListener(MouseEvent.ROLL_OVER, startAnimation);

areaName.addEventListener(MouseEvent.ROLL_OUT, rewindAnimation);

function startAnimation(evt:MouseEvent):void {

     animation.play();

}

function rewindAnimation(evt:MouseEvent):void {

     stage.addEventListener(Event.ENTER_FRAME, reverseAnimation);

}

function reverseAnimation(evt:Event):void {

     if(animationName.currentFrame > 1){

          animation.prevFrame();

     } else {

          stage.removeEventListener(Event.ENTER_FRAME, reverseAnimation);

     }

}