The Experience vs. the Explanation of Neurological Disease


At the conclusion of stroke conference today, we watched a TED talk by Jill Bolte Taylor, the Harvard neuroanatomist who suffered a left hemispheric hemorrhage due to AVM rupture. She’s written a popular book about her experience of neurological deficit during her stroke and her observations about the health care she received. Her TED talk is one of the most viewed of all time–over 12 million so far–and for good reasons: Her story is lucid, insightful, and quite moving.

Prof. Taylor’s neuroscientific explanations warrant further scrutiny, however. Her main thesis is that the right hemisphere is a “parallel processor”, sensing the various forms of energy around us but not imposing a strict delineation between self and non-self. The right hemisphere experiences only the present and doesn’t concern itself with past and future. The left hemisphere, in Taylor’s view, is a “serial processor”, picking out discrete aspects of the input reaching the brain, naming them, and ordering them in terms of past experience and future planning. The left hemisphere is dominant, which accounts for the fact that we are constantly differentiating and judging the things we experience, worrying about the past, and planning for the future. When the left brain is injured, however, or suppressed through meditation, the right brain is free to emerge, allowing us to experience the interconnection of everything in the universe and attain relief, enlightenment, nirvana. Indeed, one of the most fascinating aspects of Prof. Taylor’s story is that there were times when she did not want this experience of one-ness to end.

The following analyses are based on the method of analytical philosophy as applied to neuroscience by Bennett and Hacker. Disclosure is warranted here: I’m not a philosopher. But I am interested in being the best neurologist I can be, so I try to bring as much conceptual rigor to my practice as I do clinical rigor.

Here goes: It does not make sense to say that one hemisphere of  the brain experiences or processes anything. Nor does it make sense to say that the brain (much less a hemisphere thereof) names, orders, judges, or plans anything. People do those things. People have, we believe, the most highly-developed cognitive capacities of all creatures, and the exercise of those capacities requires healthy brains. Injuring the brain disrupts our exercise of those capacities, and much of the history of neurology consists of correlating the site of nervous system lesion with the cognitive, sensory, motor, or other dysfunction that results. Occasionally, such disruption may even result in a positive experience, such as Prof. Taylor experienced during certain moments of her illness. However, the fact that a left hemispheric insult resulted in such a positive experience does not mean that the right hemisphere is “responsible” for such experiences, and it certainly doesn’t mean that the right hemisphere itself experiences anything.

Here’s another recent example of this kind of conceptual difficulty. It comes from a neuroscientist who studies neuromodulatory chemicals such as dopamine and who developed Parkinson’s disease. He wrote a moving piece in the journal Nature a few weeks ago, in which he describes his initial symptoms and his struggles with both the disease itself and the effect it is having on his sense of self and his career. It’s another narrative worth reading–we in neurology should be connoisseurs of patient narrative–but I want to focus on this passage:

Take the very peculiar symptom known as ‘freezing’. Occasionally, when I attempt to lift my hand it well … won’t. Notice that I didn’t say can’t. There is nothing wrong with my arm. It is still strong and capable of moving, but I have to put effort, even focus, into getting it to move — frequently to such a degree that I have to pause whatever else my brain is doing (including talking or thinking).

(Hat tip to Andrew Sullivan, on whose excellent blog I found this).

It is true that there is nothing necessarily wrong with the arm of a Parkinson’s patient, and confrontation strength will usually be normal. Arguably, however, the arm is not capable of moving–at least not normally. For one, it is a person who is capable (or not) of moving his arm–not the arm itself that has such capability. Further, it is this very capability of movement that is so impaired in Parkinson’s disease! A major aspect of the disease is that patients lose the capability to move their limbs they way they want and need to. The author clarifies that his exercise of the capability to move his arm requires focused concentration; this statement is unproblematic. But then he states that he must pause “whatever else my brain is doing ,” such as talking or thinking. Again, it is not his brain that is doing the talking or thinking–it is he. Here’s how I would re-write that paragraph:

Take the very peculiar symptom known as ‘freezing’. Occasionally, when I attempt to lift my hand it well … won’t doesn’t. Notice that I didn’t say that I can’t move it at all. There is nothing wrong with my arm. It is still strong and capable of moving, but I have to put effort, even focus, into getting it to move — frequently to such a degree that I have to pause whatever else my brain is I am doing (including talking or thinking).

Why all this fuss about language? It’s not just fastidiousness for its own sake. The concern here is that these conceptual confusions are often invoked to explain how the brain functions. And since we’re neurologists, trying to learn how the brain functions so that we can help our patients, it is very important that we approach that task with intellectual rigor.

One way to think about this is to put it in the context of the diagnostic method that we use over and over again clinically: First, we start with a syndromic diagnosis (and sometimes we end there, unfortunately). But the beauty of neurology is in determining the anatomical diagnosis (“where’s the lesion?”) and the etiological diagnosis (vascular, neoplastic, degenerative, etc.) Understanding our patients’ problems at a deeper neuroscientific level is simply a refinement of the etiological diagnosis, but this requires the same conceptual rigor as the antecedent diagnostic formulation.

For example, it (usually) doesn’t make sense to say that the chief complaint is “stroke”–most often the chief complaint is “weakness” or something of that sort. It’s not desirable to say that the neurological problem localizes to the “left middle cerebral artery”, but rather that it localizes to the left frontal and temporal lobes; once we decide that the problem is indeed stroke, we can proceed to determine the arterial distribution. It’s definitely not correct to say that the MRI shows a stroke–it shows a focus of restricted diffusion, most likely representing a cerebral infarction. Using these concepts and terms properly is the key to becoming an expert neurologist, and the same applies to neuroscientists as well.

About Justin A. Sattin

I'm a vascular neurologist and residency program director. I created this blog in order to share some thoughts with my resident and other colleagues, and to foster my own learning as well.
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