Neuroscience & the Soul

The nature of the human soul and that of the souls of other organisms has been studied extensively since Socrates, Plato, and then Aristotle went to work on the questions.  The brain, by contrast, has been accessible only very recently.  I expect that neuroscience is poised to tell us a lot about both the brain and the soul. 

One thing that neuroscience has determined, in my view, is that Cartesian dualism (or substance dualism) is untenable.  This is important because dualism remains the de facto view in the popular imagination.  Human beings (and maybe dogs, if indeed they all go to Heaven) have two complete bodies: a material one and an immaterial one.  At death and sometimes a bit earlier the latter cuts its ties with the former and drifts free.  The immaterial self is the genuine self; the material body is a mere vehicle.  The immaterial soul is the home of our thoughts, passions, and essential self. 

I like to note in passing that substance dualism may be what most Christians believe today but it is not the teaching of any major church.  The teaching of the churches is that of the resurrection of the body, suggesting that a human being without a human body is not really thinkable. 

Michael Gazzaniga’s famous split brain experiments pose a powerful challenge to substance dualism.  Gazzaniga examined patients who had had the corpus callosum cut as a therapy for extreme seizures.  This is the thick cable of nerves that connects the two hemispheres of the brain. 

Gazzaniga devised an experiment that had such a patient look at a dot on a screen.  Then a word was projected on the screen to the right of the dot.  This meant that only the right eye could see the word.  When he asked the patient to identify the word, the patient had no problem.  He would say “cat”.  That is because the right eye is wired to the left hemisphere of the brain and the latter is where the language centers are located. 

Now what happened when a word was projected to the left side of the dot?  The patient could not say what the word was.  See above.  However, and this is the fascinating part, the patient could draw a picture of the named object with his left hand.  That is apparently because the more artistic, image processing modules of the brain are located in the right hemisphere.  Whereas the left hemisphere could respond with language, the right hemisphere could respond only with a picture. 

If substance dualism were correct, and the seat of consciousness is an immaterial soul that is somehow connected to the physical body and brain, then this experiment shouldn’t have worked that way.  Information gathered by one half of the severed brain should have been uploaded to the uncut, immaterial soul.  It should then have been available to the other hemisphere, since the soul both receives information from the physical senses and commands the physical body.  That is precisely what did not happen. 

Instead, cutting the corpus callosum effectively cut one human being into two.  As long as the patient is looking at the world with both eyes, the two halves of the brain are working in tandem.  The two half-brains in one skull are not aware that anything has changed.  They can navigate the world well enough that no one else knows the difference, unless he is a neuroscientists conducting a clever experiment. 

Aristotle proposed (de Anima) that the soul was the actuality of life in a body with the potential for life.  Just as heat is the actual temperature of a physical medium that can be more or less hot, so the soul is the actual state of a living body that can be alive.  Aristotle was right.  Descartes wrong and so is Walt Disney.  Neuroscience can now tell us a lot about the soul because it is exploring the brain. 

Science Daily describes a study that linked a willingness to punish violations of moral rules with specific regions in the brain. 

The results of the study show that people only punish norm violations at their own expense if the dorsolateral prefrontal cortex – an important area for control located at the front of the brain – is activated. This control entity must also interact with another frontal region, the ventromedial prefrontal cortex, for punishment to occur.

The communication between these two frontal regions of the brain is also interesting in light of earlier fMRI studies, which showed that the ventromedial prefrontal cortex encodes the subjective value of consumer goods and normative behavior. As neuroscientist Thomas Baumgartner explains, it seems plausible that this brain region might also encode the subjective value of a sanction. This value increases through the communication with the dorsolateral prefrontal cortex. «Using brain stimulation, we were able to demonstrate that the communication between the two brain regions becomes more difficult if the activity in the dorsolateral prefrontal cortex is reduced. This in turn makes punishing norm violations at your own expense significantly more difficult.»

This study illuminates the neurological substratum of one of the key moral emotions, which in turn underlies moral behavior.  We are looking here at the activity of parts of the human soul. 

This is not, as one might worry, a reductionist account.  The activity of the various regions of the brain can only be understood in light of the moral activity that defines human action.  As a door knob depends on the existence of a doors, so the dorsolateral prefrontal cortex can be what it is only because it is part of a larger whole.  The parts are subordinate to the whole.  The material is what it is shaped into.  The soul is the actuality of the body. 

Aristotle's Four Causes

While reading Nagel’s proposal for a more complete, trans-physical account of nature, it occurs to me that the mind/body problem doesn’t seem to appear in Aristotle’s work at all.  To be sure, Aristotle was a vehement anti-reductionist.  This is especially evident in his remarks on Empedocles.  The latter argued that the curvature of the spine is a result of the confinement of the fetus in the womb, which is the kind of thing you have to argue if you want to maximize the role of chance in all physical explanations.  Aristotle rightly supposed that such features of anatomy have a species-cause. 

By contrast, Aristotle saw no tension at all between materialist and mechanical explanations, on the one hand, and formal and teleological explanations on the other.  Consider his famous account of the four causes.  Here is the translation from my old Charlton edition of the first two books of the Physics.

[1] According to one way of speaking, that out of which as a constituent a thing comes to be is called a cause; for example, the bronze and the silver and their genera would be the cause respectively of a statue and a loving cup.  [2] According to another, the form or model is a cause; this is the account of what the being would be, and its genera‑thus the cause of an octave is the ratio of two to one, and more generally number‑and the parts which come into the account.  [3] Again, there is the primary source of change or the staying unchanged: for example, the man who has deliberated is a cause, the father is the cause of the child, and in general that which makes something of that which is made, and that which changes something of that which is changed.  [4] And again a thing may be a cause as the end.  That is what something is for, as health might be what a walk is for.  On account of what does he walk?  We answer ‘To keep fit’ and think that, in saying that, we have given the cause. 

Cause here translates aitia, a word that philosophy borrowed from forensic language.  It originally meant responsibility, as in who done it.  In Aristotle’s work, it implies an answer to a certain kind of question. 

Aristotle provides helpful examples in each case, but I will expand one of his examples to cover all four cases.  Consider the development of a human being from conception to birth.  How does one explain this process?  One obvious answer is that the developing person comes to be out of certain kinds of material, which the scholarship refers to as material causation.  Another answer is that the human being comes to be because the developing being is human in species.  This is formal causation.  A third answer is that Da knew Ma and got things rolling.  That is efficient causation.  Finally, the developing being develops toward a predetermined end, according to a program that was present at the very beginning.  That is final causation. 

I think that this is dead spot on.  An organism, human or otherwise, comes to be because it comes to be out of certain kinds of material, just as a functioning machine is an arrangement of materials moving and changing in certain ways.  I doubt that there is anything going on in a human body or mind that does not have a material substratum. 

An organism comes to be from existing organisms of the same species.  Cats give birth to cats and never to catfish.  Aristotle recognized that the species form had to exist in two versions: the expressed organism (what we would call the phenotype) and the implicit form transmitted in the act of conception (the genotype).  Aristotle thought that the latter was introduced by the father, whereas the mother supplied only the matter.  We know better, but it doesn’t change the general scheme. 

Efficient causation is what happens when an existing system is destabilized from outside.  The father destabilizes the mother by introducing his semen.  However, in the case of a developing organism, the force of efficient causation does not scatter like billiard balls.  Instead, it gathers toward a predetermined end, guided by the species form.  Final or teleological causation is an obvious fact of ontogeny. 

Aristotle’s four causes make up a correct and comprehensive set of biological explanations.  What is striking, from the viewpoint of contemporary philosophy, is that he didn’t see any conflict between material and efficient causation (which modern physical science has long wanted to rely on exclusively) and formal and final causation.  He wasn’t the least bit worried about reducing the latter to the former nor did he desire it. 

I suspect that one of the reasons for this is that Aristotle begins with biology.  While his writing aims at a comprehensive account of nature, his preoccupied with animals.  Modern science is beginning to come around to Aristotle’s way of thinking, through no fault of its own.  The long dominion of physics, which began with the advent of modern science, is probably at an end.  Biology is the most important of modern sciences just now, and that is good for science.  It may be that living organisms have more to teach us than anything else in the visible Kosmos.