What could cause a cold sensation in the forehead?

This happens to me a few times a day. It's very similar to the brain freeze one can get when starting to eat something like ice cream, but it's isolated to one small area. It comes on suddenly, lasts for a couple of minutes, and sometimes the cold sensation will spread to the top of my head or around to the base of my skull. Then, it goes away. I was diagnosed with hyperthyroidism three months ago, and have been taking Methimazole for it. I'm wondering if either the thyroid condition or the medication could be causing this odd sensation.