Tuesday, August 02, 2005

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.

"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."
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:
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.

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.
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.

11 Comments:

Blogger David said...

The psychology-neuroscience distinction is technically false, sure, but it might be a useful one. Is it really meaningless to talk of mental phenomena as if they existed in a separate plane from biological phenomena? Extending that notion, one might argue that it’s meaningless to talk of socioeconomic trends as if they existed in a separate plane from particle physics. From a purely materialistic standpoint they don’t, but it turns out to be useful and necessary to choose levels of analysis relevant to the topic of study, thus the molecules of chemistry, the cells and tissues of biology, the populations of ecology/sociology and so on. It’s all particle physics, to be sure, but at certain points it’s absurd to proceed without switching lenses. It may prove to be true that the denial caused by a traumatic childhood is implemented at a string-theoretical level by strings and p-branes and so on, but so what?

In neuroscience, the neural systems and processes from which “higher order” functions emerge are still too poorly understood for the field to subsume all of psychology, speculative pseudoscience and all. It’s not even clear where in the brain the lenses might usefully be switched—neurotransmitters, neurons, cortical columns, gyri and lobes, probably, but where else? Until a clearer picture emerges, the phrase “psychological phenomenon” will still serve as a useful flag for areas where neuroscience has yet to develop useful explanatory or predictive power. At the very least, modern neuroscience imposes the burden of proof on would-be Freuds tempted to pull a theory of mind and behaviour out of empirical thin air.

8/04/2005 06:32:00 PM  
Blogger Andrew said...

Yes, I absolutely agree that it is useful - and, indeed, meaningful - to distinguish between different levels of explanation, some being more appropriate and useful for certain phenomena than others. That's what I meant by "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."

Daniel Dennett (I know I go on and on about Dennett, but he has a lot of cool ideas!) coined the phrase "greedy reductionism." We all love reductionism and it's great, but we have to be careful to be smart reductionists, not "greedy" reductionists - i.e., let's not delude ourselves that we can explain socioeconomic trends in terms of particle physics. He gives the example of a calculator - it's true that the calculator works because of a certain pattern of electron flow, but if you want a meaningful and useful explanation of how the calculator works, you have to look at the higher-order level of how the logic circuits are put together. What we "smart" reductionists want is to be able to explain each higher-order phenomenon in terms of something slightly lower-order - as you say, switching lenses as you go along.

I wanted to highlight the fundamental continuity of biology and psychology because I think it's a major conceptual blindspot a lot of people have. Many people still unconsciously subscribe to dualism, and it takes a bit of a mental shake-up to really get that the mind is "just" an emergent property of the brain. The phrase "psychological phenomenon" has to be re-framed as not being on a totally separate plane of reality, but just in a certain "region" on a scale of complexity - as a useful flag, not a reified, separate Ding an sich.

Historically, materialism has bubbled up from the lowest level - two centuries ago, people still thought that living things had a "vital force" that couldn't be explained simply in terms of chemistry. Now we know differently, even though after decades of research we still can't predict how a protein will fold from its amino acid sequence alone. I think it's the same with the neuroscience-psychology connection, just one level higher.

8/05/2005 01:08:00 AM  
Blogger David said...

Thanks for the reply. Cool blog, by the way, I just stumbled into it today.

8/05/2005 03:32:00 AM  
Blogger Andrew said...

Glad you like the blog - I hope you come back in the future (and comment more)!

8/05/2005 07:56:00 AM  
Anonymous Katie said...

I really liked this entry... Over the past few weeks, I've been dealing with a loved one's schizophrenia diagnosis, and trust me, you really get a whole new appreciation for the biology/psychology debate when you're trying to explain things to family members. "No, he can't just 'snap out of it'"...

But I found this article interesting when they talked about the lack of insight that patients had regarding their disease...this is a symptom of other mental illnesses. Is it possible some illnesses knock out those brain regions that recognize what's 'normal' functioning? Or is it more complex than that?

8/05/2005 07:29:00 PM  
Blogger Andrew said...

Katie,

I'm glad you liked this entry! I'm sorry about your loved one's schizophrenia diagnosis; and I agree that the "can't he just snap out of it?" reaction is still sadly all too common.

I do think that awareness of normal functioning is more complex than knocking out the "awareness" brain region - for the simple reason that consciousness and awareness are not properties of the mind that can be localized to any one brain region, but rather emerge out of the interactions of all your neural circuitry.

Another example is Capgras syndrome, where patients believe that their loved ones have been replaced by look-alike strangers/robots/aliens. It's thought that this happens because the parts of the brain that mediate emotional reactions to faces is damaged, though the parts that recognize faces are not, so the patient recognizes his/her loved ones but fails to feel the expected emotional reaction - and the only apparent way to explain this strange perception is the delusion that your mother isn't "really" your mother.

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