In "Descartes' Error" Antonio Damasio showed that, contrary to what Descartes made

us believe, also our normal, calm reasoning, our common sense, is

controlled by our emotions and our body. The following anecdote is described in the book to illustrate this main point.

You may imagine Damasio and his colleagues, a room-full of researchers in white coats, sitting and listening and taking notes, while a patient is thinking aloud, trying to decide when to schedule his next appointment. Tuesday has its advantages, but so does also Thursday. For about half of an hour, until he is finally interrupted, this patient is going through a thorough rational analysis of pros and cons of Tuesday vs. Thursday, while it is obvious to everyone else in the room that he doesn’t have much to do anyway, and that both Tuesday and Thursday are equally fine. Why is then everyone listening so attentively to that nonsense?

 
Because they are witnessing a clear demonstration of Descartes’ error.

The patient they are listening to had a part of his brain removed in an operation, which had the effect that his conscious mind was disconnected from the emotional imprints stored in the body. The consequence is that this patient is able to exhibit perfect Cartesian rationality, while he lacks the ability to separate that which is relevant from that which is not. The body, concluded Damasio,

performs this function for us, acting as a sort of a filter. Out of a myriad of possible ideas, whims and impulses, our body eliminates a vast majority and presents to our conscious mind only those

which are ‘reasonable’ or ‘appropriate.’ From the point of view of the body, of course.

It is not difficult to see why the evolution needed to provide this sort of filter as well. Our sensory organs receive far more information than our conscious mind is able to process. Most of this information has to be digested, filtered and presented to our conscious mind through subliminal, embodied processing. Being embodied and subconscious, this centrally important filter can be programmed, through sensations, feelings and subliminal messages. But this means that our seemingly rational choices too can be programmed in the same way!