The answers below are good. It is not technically measured on the Scoville scale.
But I lived in Japan for two years and Mexico for nine, so I am quite familiar with voltage. I find it interesting that some roots, such as wasabi, put the burn up into your sinuses, but your tongue and throat are fine, and the burn doesn’t linger, while others (chiles, mostly) work on the front of the mouth — lips, tip of the tongue, and still others linger and linger in the back of the mouth and top of the throat.
Also, to be vulgar for a moment, you don’t feel wasabi twice, at both ends of the digestive system, whereas if you have a particularly hot Mexican dish, well hello there, the next morning, I’m wide awake NOW!!!