In the philosophy of mind, I have read that "intentionality" is a difficult thing to explain in a naturalistic fashion. But I don't necessarily see the heart of the problem in the same way that explaining "qualia" poses difficulties for naturalism. When somebody asks me to picture Tokyo in my head, a mental image pops up that represents or is "about" Tokyo. Where is the mystery? Why can't I simply say that my mental image of Tokyo exhibits certain properties which my brain relates to Tokyo (big buildings, busy traffic, etc)?
One way in which I've heard it explained is via a regress problem. If intentional thoughts exist, they must be somehow connected to other intentional thoughts. That is, they cannot be isolated if they are to be truly intentional thoughts. Therefore, if a naturalist tries to say that my thought about Tokyo can be isolated to a specific firing of neurons, he/she would have to concede that my thought cannot be intentional in the first place. But I don't understand what is meant by intentional thoughts being unable to be isolated from other intentional thoughts, or why this must be the case.
Can somebody point me in the right direction here?