There is a dearth of cognitive psychologists on this site, I can't speak to their explanations of cognitive process, but none are needed to prove thoughts exist. How can they be denied? The proof is self-evident.
Everything that was ever rendered by human effort grew from an initial thought, just as our opinions of them do.
Cogito ergo sum : I think, therefore I am.
-Rene Descartes
I've never heard the concept of thought come into question . . . I mean there a great number of theories regarding the physical world being real, but that "Thought" was pretty much a given. One of the more interesting is hard solipsism, where you could be just a brain in a vat, and the entire universe you interact with is merely your creation using nothing more then thought . . . .
Nothing specific I could find on the internet, but here's a bit of general information.
In 387 BCE, Plato is known to have suggested that the brain was the seat of the mental processes.
Cognitive psychologists are often heavily involved in running psychological experiments involving human participants, with the goal of gathering information related to how the human mind takes in, processes, and acts upon inputs received from the outside world.
I think therefore I am. I feel therefore you are.
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