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Executive dysfunction

I’ve been doing some refresher reading on dementia and in particular, on the particular symptom of executive dysfunction.

In recent days, the man who holds the highest office in the US, the commander-in-chief of a nuclear-equipped military, has been proudly announcing that he is not demented, because he passed a test called the MoCA. Possibly coincidentally, one of the medical sources I follow published an article discussing dementia cases in which memory loss was only a minor feature, with the primary problem being a loss of executive function. So, I decided to read up on the subject.

So what is this test that the President took? The MoCA is a dementia screening tool. It’s not the one I was taught in med school, so I thought I’d read up on it a bit. And, it does seem to test a wider set of cognitive skills than the one I learned, so that’s cool. In addition to simple memory, the MoCA also tries to screen for dysfunctions of attention and concentration, executive functions, language, visuoconstructional skills, conceptual thinking, calculations, and orientation. 

See, when someone says “dementia”, we think about the classic presentation of Alzheimer’s disease – a progressive loss of primarily short-term memory. Less obvious but extremely important are other lost functions as the brain degenerates. Neurological degeneration can cause problems with movement and coordination – such as you see in Parkinson’s disease. It can cause specific difficulty with use of language, as with frontotemporal dementia. People with neurological disease can lose their ability to manipulate numbers and perform mathematical calculations, or lose their ability to draw out common items with correct spacial orientation – for example, arranging the numbers on a clock face appropriately. Damage to any of these domains can significantly impair a person’s ability to live a functional and independent life.

But when it comes to a man in a powerful office, one subtle and really important aspect of dementia strikes me as especially important. This is the appropriately-named “executive function”, which assesses how well a person can integrate all the other information available to make a rational and effective decision. Executive function is what lets you pull it all together – to use your fund of knowledge, your working memory of recently-collected information, your physical and spacial and mathematical skills, and your understanding of priorities and goals to make a good plan. It’s what allows you to be flexible, to adjust to new input, and to control your impulses.

And because executive function is the brain functioning at its most complex, it’s very hard to test for. For one thing – if an individual fails at a task that requires pulling together several different brain functions, how do you tell whether the failure was at the “pulling together” or at the basic brain function to begin with? For another, it’s hard to come up with a task that stretches to brain to incorporate many complex inputs, while still being quick and simple to administer. And, it’s a challenge to design questions or tasks with a single clear, reproducible, quantifiable answer when the goal is to see how flexible and creative the brain is capable of being.

So, executive functioning assessment feels a bit like the classic definition of pornography – “You know it when you see it”. When executive functioning begins to fail, people begin to make bad decisions. They may appear to have forgotten or never understood likely consequences to action. They seem impulsive. Because their brains don’t switch easily between ideas, they cling to a single idea and repeat themselves a lot. If the situation demands that they integrate multiple ideas to form a clear picture, they tend to fail; their response simply doesn’t make sense. They don’t make very good plans, and even when they make a good plan, they’re not very good at following it.

So how does the MoCA try to measure executive function? Basically, it asks the testee to complete a task that requires switching back and forth between two ideas. In the visuo-spacial arena, it uses a connect-the-dots type puzzle where the goal is to alternate letters and numbers. So you’d be connecting 1 to a, then to 2 and then to b, and so on up through 5 and e. It requires that you hold your progress along the alphabet in mind while you look for the next number, and then remember you’re supposed to switch back to letters once that number is found. Then your performance is compared to how you do when you’re asked to connect just numbers or just letters – so if the problem is with just letters or numbers, that’ll show up.

Additionally, there’s a test where you’re asked to think of as many words as you can beginning with the letter f. This requires you to remember words and, as you do so, filter out the words that start with a “ph” instead. And there’s a test where you’re asked to figure out what a couple of words have in common – like “train” and “bicycle”, requiring you to define both words and think through how they relate to one another.

So how well does the MoCA test for executive dysfunction? I spent a fair bit of time googling that question and the answer is a firm “I’m not sure”. It appears that the MoCA is genuinely better at catching cognitive impairment with executive dysfunction than earlier tests – but that doesn’t make it perfect. When the test was introduced, it claimed 90% sensitivity for detecting cognitive impairment – that is, 9 out of 10 people with a real problem would fail this test. But some later evaluations found a higher rate of failure than that. So that tells me that overall, the test would miss some impaired subjects. Further, the test is geared for people with 12 years of education and average intelligence. People with higher levels of native ability and training could be fairly impaired and still perform just fine on it.

Meanwhile, the inventor of the MoCA has announced that the test, formerly available for free, will shortly be transitioning to only be available for physicians to use after they’ve completed a short training course in administering it. Apparently an analysis of real-world test results have shown that a patient may have wild variability in results within a short window of time, when the test is administered by different people. This suggests that the validity of the test is quite operator-dependent. A physician who was motivated to declare his patient competent might administer the test quite differently than one whose biases leaned in the other direction.

So, the President performed well on a test which is pretty good – but not perfect – at identifying patients with cognitive decline. The validity of that test will be decreased by the President’s educational background as well as the innate biases of the person administering the test.

But I do offer one last point as food for thought in this situation. The MoCA test is not a standard thing to include in any routine physical exam. For that particular test to be administered means that someone – the President himself, or his physician, or someone very close to the situation – felt that it was medically appropriate to administer a dementia test, and chose the particular dementia test designed to best catch executive dysfunction. And that suggests that whether or not there’s actually an organic dementia problem, the President does have a problem with observably irrational behavior.

Sadly, I can’t do much about that except to make certain my vote is counted this November. But at least I know a lot more about the current state of cognitive screening now.


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