2012 vs 2011 Prius - Any mechanical updates between these?

So I'm trying to figure out whether to get a prius thats 2011 IV package or the 2012 III. Price and mileage are somewhat close but I'm leaning towards the IV due to it being leather seats and a thousand less.

Any mechanical updates occur between these years? I do know of the cosmetic changes that occured with the bumpers, but couldn't find anything that changed mechanically like intake manifold or other parts.