Does Descartes explain or define how the sensation mechanism works?

Question

Especially in Meditation 2, Descartes uses "sense", "sensation" many times when he argues for the mind-body distinction. But does he explain the sensation mechanism?

I wonder this because it seems to me that he just reduces sensation to the body. I say "reduce" since our body parts are just receptors and do not process inputs to make what he called "sense" or "sensation".

Another question: Does Descartes consider his brain a part of his body? If so, in Meditation 2, when he is not sure about his body, does that mean he is not sure about his brain?

Answer 1

We have to see Descartes on physiology and psychology.

The main references are :

• L'Homme, the last chapter of The World, also called Treatise on the Light (Traité du monde et de la lumière), written between 1629 and 1633, published separately as De Homine in 1662;

and :

• Les passions de l'âme, completed in 1649.

From L'Homme :

Part I : On the machine of the body

These men will be composed, as we are, of a soul and a body. And I must describe for you first the body on its own; and then the soul, again on its own; and finally I must show you how these two natures would have to be joined and united so as to constitute men resembling us.

Next, in order to understand how the external objects that strike the sense organs can instigate the machine to move its members in a thousand different ways, note that the tiny fibres (which, as I have already told you, come from the innermost part of its brain and make up the marrow of the nerves) are arranged in every part serving as the organ of some sense in such a way that they are easily moved by the objects of that sense.

Now I hold that when God unites a rational soul to this machine, as I intend to explain later on, He will place its principal seat in the brain and will make its nature such that the soul will have different sensations depending on the different ways in which the nerves open the entrances to the pores in the internal surface of the brain.

Part 5 : On the structure of the brain of this machine, and how the spirits are distributed there so as to cause its movements and its sensations

Here the disussion is centered around the role of The Pineal Gland.