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.