Anosognosia and the mind-body problem (literally)
Via the NYTimes comes news of this study (Pubmed link) showing that damage to the supplementary motor cortex (see simplified diagram at bottom of post) causes a fascinating syndrome called "anosognosia" in which patients are paralyzed but persistently deny the paralysis, often coming up with elaborate confabulations to explain away why they cannot move their arm:
Dr. Anna Berti sits facing a patient whose paralyzed left arm rests in her lap next to her good right arm. "Can you raise your left arm?" Dr. Berti asks.The NYTimes does a fairly good job of explaining the theory behind why damage to the premotor cortex would create this strange perception in anosognosic patients, so I won't rehash it. (It's very interesting, so do read the article!) What I want to address is this bit:
"Yes," the patient says. The arm remains motionless. Dr. Berti tries again. "Are you raising your left arm?" she asks.
"Yes," the patient says. But the arm still does not move. ... If prodded for hours, patients will make up stories to explain their lack of action, Dr. Berti said.
One man said his motionless arm did not belong to him. When it was placed in his right visual field, he insisted it was not his. "Whose arm is it?" Dr. Berti asked.
"Yours," he said. "Are you sure?" Dr. Berti persisted. "Look here, I only have two hands."
The patient replied: "What can I say? You have three wrists. You should have three hands."
This denial, Dr. Berti said, was long thought to be purely a psychological problem. "It was a reaction to a stroke: I am paralyzed, it is so horrible, I will deny it," she said.This is a false distinction. All psychological phenomena are rooted in neurology, because the mind is the product of the brain. Now, it is meaningful to talk of some phenomena as being "higher-order" and others as "lower-order" in terms of how easily they can be explained by the biology. In this case, we could distinguish the kind of denial caused by crude brain damage (anosognosia) and the kind of denial caused by, say, a traumatic childhood (or whatever; I'm not up on my psychoanalysis). But it is not meaningful to talk of mental phenomena as if they existed in a separate plane from biological phenomena. Even denial caused by a trauamtic childhood (or whatever) would still be implemented as a neurobiological level by neurons, synapses, and so on. It is nonsensical to talk about something as being "purely" a psychological problem.
But in a new study, Dr. Berti and her colleagues have shown that denial is not a problem of the mind. Rather, it is a neurological condition that occurs when specific brain regions are knocked out by a stroke.