browser_ok = document.images;						//  Use object detection to check for support of the images array

if (browser_ok ) 
{													// if proper browser type, then preload images 
show1on = new Image();								// preload images activated when mouse moves over menu 
show1on.src = "images/brain_upperleft_on.jpg";
show2on = new Image(); 
show2on.src = "images/brain_upperright_on.jpg";
show3on = new Image();
show3on.src = "images/brain_lowerleft_on.jpg";
show4on = new Image(); 
show4on.src = "images/brain_lowerright_on.jpg";

show1off = new Image();									// preload images activated when mouse moves off menu
show1off.src = "images/brain_upperleft_off.jpg";
show2off = new Image();
show2off.src = "images/brain_upperright_off.jpg";
show3off = new Image();
show3off.src = "images/brain_lowerleft_off.jpg";
show4off = new Image();
show4off.src = "images/brain_lowerright_off.jpg";
}

function img_act(imgName) {
	if (browser_ok) {
          imgOn = eval(imgName + "on.src");
          document [imgName].src = imgOn;
	}
}

function img_inact(imgName) {
	if (browser_ok) {
          imgOff = eval(imgName + "off.src");
          document [imgName].src = imgOff;
	}
}