Set activeLayer above current activeLayer

Hello

I want the second Layer from the bottom to be my activeLayer.

I have already selected the bottom Layer by doing this:

#target photoshop

app.bringToFront();

var background = app.activeDocument.layers[app.activeDocument.layers.length -1];

app.activeDocument.activeLayer = background;

But I do not know how to set the activeLayer to be the one directly above my backgroundlayer.

Any suggestions?