Yes, but the effect is not pronounced. I seem to do well in relatively cool, dry environments. The humidity, I think, is what affects me the most. I live in LA, which isn't exactly cold, but the humidity is always low, which makes it comfortable. But when it gets hot, my brain does get sluggish. It's true that AC helps, a lot. :)

I don't think it's cold indoors, in cold locations. Of course you can't go to sit in a park with a laptop when it's cold.