Spice – The name or chemical compound responsible for a specific quality of some spices (numbness)

I'm putting together the results of a kitchen experiment and I'd like to be able to identify a phenomenon that I've noticed when using certain spices. I've felt it in some of what are often called "warm" spices, cinnamon, clove and nutmeg come to mind, but that's by no means a complete list. For lack of a better way to describe it, it's a subtle numbness. I feel it primarily on the hard palate, and the sensation (or lack thereof) lasts perhaps twice as long as the perception of the actual flavor of the spice. It's so subtle that it won't surprise me if nobody knows what I'm talking about, but I'm hopeful.