Your neurons exist, but your thoughts do not. When you picture a keyboard, you, like everybody, can close your eyes and imagine what it would be like to see and feel a keyboard if you were in front of one. That doesn't mean that that keyboard exists or has ever existed -- and by "exist", I mean, of course, that it lies somewhere on the physical plane. To say that your thoughts exist would be to say that you could pick them up if you wanted to, which is nonsensical.