Cartesian materialism is an attempt to keep the mechanistic metaphysics of Descartes while getting rid of the idea on an immaterial soul (dualism). In this philosophy, the mind is seen as a (material) component of the body (e.g. the brain or some component of it) that interacts with the world via the senses and muscles. The philosopher Daniel Dennett has proposed the term "Cartesian theater" to summarize the picture that results when this idea is combined with the reflection-correspondence perspective: the mind somehow sits in a theater where the incoming perceptions are projected as images onto a screen; it looks at them, interprets them, and decides what to do; it sends its decisions as commands to the muscles for execution. In a more modern metaphor, we would describe the situation as if the mind acts as a control center for the body, the way an air traffic controller keeps track of the incoming planes on a radar screen, analyzing the situation, and issuing directions to the pilots. While this picture may seem more satisfying to a scientifically trained mind than Descartes' ghostly soul, it merely shifts the difficulty.
The fundamental problem with the mind as control center is that it is equivalent to a homunculus (diminutive of the Latin "homo" = human being): a little person watching the theater inside our brain, and reasoning like an intelligent being in order to deal with the situation it observes. However, the point of the exercise was precisely to explain how a person reasons! We have explained the mind simply by postulating another, "smaller" mind (homunculus) within the mind.
Such reasoning leads to an infinite regress. Indeed, to explain how the homunculus functions we must assume that it has a mind, which itself implies another homunculus inside it, which must contain yet another homunculus, and so on. It is as if we are opening a series of Russian dolls the one nested into the other one, without ever coming to the last one. Another way to illustrate the circularity of such reasoning would be to consider a recipe for making cake where one of the ingredients is cake: how can you ever prepare such a cake if you don't already know how to do it? To evade this paradox, we need to make a radical break with the way of thinking that produced it.
The need for a systems view
To stop such an infinite regress, we need to posit a place where it ends: the component of our brain where consciousness resides and where rational decisions are made. But unless we go back to Cartesian dualism, and postulate a mysterious, ungraspable soul, we will not find such a place where the outside world ends and the true mind begins. Indeed trying to pinpoint the place where decisions are made, we still come to the conclusion that that place must be able to perceive what is going on outside of itself, and therefore that it must have a seat in the theater, bringing us back to the homunculus reasoning.
The attempt to situate the mind in a specific place or separate component is a remnant of reductionism, the philosophy that explains all phenomena by analyzing them into separate parts, and then determining the properties of the parts. We should understand the mind not as a collection of parts, but as a whole, which is distributed over many components. It is not located in any one of them, but in the network of their relations or interconnections. Different parts of cognitive processes take place in different parts of the network, but there is no single part where everything comes together, no "seat of the soul". We should also accept that there is no one-to-one correspondence between mental and physical components: the mind as a whole stands in a complex relationship to the world as a whole. Mental components do not behave like static, independent objects. They are part of a dynamic network of relationships: a process. Such a holistic and dynamic perspective requires a new scientific worldview, which we can find in evolutionary cybernetics.