In order to get a correct idea of the operations of thinking, one should consider the brain as a special organ intended purely for mental work: just like the stomach and digestive intestines. We see how food with certain properties enters in, and we see how it comes out with completely new properties, and we come to the conclusion that it is inside that the cause of this change is located. In a similar way we see how impressions reach the brain through the nerves: they are now isolated and have no connection with the outside. The brain takes action and begins to process them: and soon turns them into a concept...
And we also confidently conclude that the brain digests these impressions in a certain way.
Pierre-Jean-Georges Cabanis: Ueber die Verbindung des Physischen und Moralischen in dem Menschen