Highlight slide

I have a VB project that opens PowerPoint presentations on a dual-monitor system. On the left side (the VB application) is a screen that looks like powerpoint slide sorter mode. When a slide is clicked on the VB monitor, it's highlighted (with a black rectangle around it) and that slide is maximized on the other screen in slide show mode. When Page up and Page down are pressed on the keyboard the next/previous slide are shown on the slide show monitor. I need the slide to be highlighted that is up on the slide show monitor when page up and down are pressed. Does anybody know how I could do this (if this makes any sense to anybody!)? Thanks in advance.