Descartes Passions of the Soul

A strangely compelling yet naive argument for why consciousness resides in the pineal gland

Descartes is famously considered a dualist, an unpopular position among modern-day brain scientists, which says there’s a fundamental division between mind and body. On the face of it, dualist philosophy suggests there’s something non-physical to our psychology, that experience isn’t reducible to brain cells or neurotransmitters. But there’s plenty of space for nuance, and Descartes is a complex man. He talks about “spirits”, which he defines as a sort of consciousness- or experience-particle. The interesting thing about these non-physical experience-particles is that, according to Descartes, they nonetheless have a physical location. From the bloodstream, spirits are pumped into the brain, where they begin reciting incantations and dancing around crackling neurons and are just generally channeling spirit energy, mystically exerting their will over neighboring brain cells.

But he gets even more precise with the location of spirits, and here, the logic is as fascinating as it is absurd. He says that our perception of the world is singular, we see a single image, we hear a single sound. In contrast to our conscious experience, our body takes in sensory information via paired sensory organs, two ears, two eyes, two nostrils, two…hands? Information from each of our sense organs are transmitted to the brain, where sensory stimuli are independently processed by each of our cerebral hemispheres. In the case of vision, one image taken in by each eye gets relayed independently to its own half of the visual cortex. And so Descartes argument was basically this - If lower level perceptual processing gave rise to consciousness, why wouldn’t our perceptions feel separate? If the neurobiology is double, why isn’t our conscious experience in a way sort of also double?

If his assumption is correct, then consciousness may emerge from a brain structure that isn’t symmetrical, where there isn’t one copy in each cerebral hemisphere, say the good old pineal gland. This is where the naivete comes in, because the pineal gland is not the only location in which discrete hemispheric brain activity is integrated (corpus callosum? any neuroscientists out there?). So the pineal was a weird choice, clearly skewed by the neuroanatomy of the day, but nonetheless, perhaps Descartes did have a point. Maybe it’s more likely that integrated hemispheric functions are the seat of consciousness, rather than two brain-impressions giving rise to a seemingly singular conscious experience.

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Selected excerpts from René Descartes The Passions of the Soul

That there is a little kernel* in the brain wherein the soul exercises her functions more peculiarly than in the other parts.

It is also necessary to know that although the soul be joined to all the body, yet there is some part in that body wherein she exercises her functions more peculiarly than all the rest. And, it is commonly believed that this part is the brain, or it may be the heart. The brain, because thither tend the organs of the senses, and the heart because therein the passions are felt. But having searched this business carefully, me thinks I have plainly found out that that part of the body wherein the soul immediately exercises her function is not a jot of the heart, nor yet all the brain, but only the most interior part of it, which is a certain very small kernel situated in the middle of the substance of it and so hung on the top of the conduit by which the spirits of its anterior cavities have communication with those of the posterior, whose least motions in it cause the course of the spirits very much to change, and reciprocally, the least alteration befalling the course of the spirits cause the motions of the kernel very much to alter.

How this kernel is known to be the principal seat of the soul.

The reason which persuades me that the soul can have no other place in the whole body but this kernel where she immediately exercises her functions is for that I see: all the other parts of our brain are paired, as also we have two eyes two hands, two ears; lastly, all the organs of our exterior senses are double and forasmuch as we have but one very thing at one and the same time. It must necessarily be that there is some place where the two images that come from the two eyes, or the two other impressions that come from any single object through the double organs of the other senses, have somewhere to meet in one, before they come to the soul, that they may not represent two objects instead of one. And it may be easily conceived that these images, or other impressions, join to hither in this kernel by intercourse of the spirits that fill the cavities of the brain, but there is no other place in the body where they can be so united, unless it be granted that they are in this kernel.

Full text can be found here