From the archives: Parkinson’s and schizophrenia

Unlike my recent “From the archives” posts, this is a post I wrote way back in 2008. I had completely forgotten about it until recently, when a woman e-mailed me to thank me for it, because she had a mentally ill son and by showing her friends my post she could get them to better understand what her son was going through. That was a really nice surprise, especially since I had written it just to say “here’s something interesting I learned in school.” Re-reading the post, I was reminded of why I wanted to be a neuroscientist for awhile. Damn you, neuroanatomy, chasing me away from my dreams! I also feel like I should go back to writing posts like this. Anyway…

This is a post about two seemingly unrelated subjects.

The first is Parkinson’s disease. It’s a disease known for striking the old, causing hands that just can’t stop shaking. In extreme cases, patients display an odd inability to initiate movement on their own. They just sit there, seemingly deprived of all movement. But if you throw a ball at them, they just might catch it. And they may find it easier to walk across a stretch of floor if it has a tiled pattern, or lines of tape, than if it’s all a single color. A bit weird.

Its weirdness factor, though, is nothing against schizophrenia’s. Schizophrenia is CIA mind control rays in the dental fillings syndrome. Delusions, hearing voices, rhyming speech, reduced emotional expression… it’s a grab-bag, and each of these issues look obviously more complicated than simple motor difficulties. Indeed, though our best science indicates schizophrenia is real, an outsider might suspect its just a random bunch of problems thrown together by the imagination of psychiatrists (this is what some people in the anti-psychiatry movement–which I had a brush with around my senior year of high school–claim.)

So why not pace myself, cover them over two posts? Here’s a medical puzzle: you know how drugs have side effects? Well, those wonderful anti-Parkinson’s drugs like L-dopa sometimes make people act as if they were psychotic. And it can be hard to get schizophrenics to stick to their prescriptions, because among other things, the drugs can make them shake a little-as if they had Parkinson’s.

What’s going on here? We aren’t talking same part of the brain. That would be bizarre–screw up a part of the brain in one direction, you shake, screw the same part in the other direction, and you become delusional? What? What possible division of labor in the neurocircuits could possibly underly such a thing? Well, that’s not what’s going on, because we know Parkinson’s involves some small parts in the center of the brain involved in motor control, specifically the substantia nigra (“black substance,” small bits of the brain that happen to be darker than most of the rest of it). Schizophrenia, involves a large area of circuitry called the mesolimbic system, with its connections to the frontal lobe, temporal lobe, and so on. Schizophrenia is more complicated there, as you’d expect from its more complicated symptoms.

What unites these two diseases is dopamine. Parkinson’s involves a deficit of dopamine in one place, which uses the stuff for one thing, while schizophrenia involves an excess in another place, which uses the stuff for other things. This is yet another example of what I’ve been hammering for the past couple weeks: drugs don’t have essences of their effects. They just have the property of being the molecules they are. All your brain sees when it sees dopamine is “another molecule of that shape,” its up to the wiring of the circuits to decide what to do with it.

As an after word, I should mention not to mentally exaggerate the schizophrenia-dopamine connection. The substantia nigra is pretty definitely run on dopamine, but the areas of the brain involved in schizophrenia are more complicated. Other neurotransmitters, such as glutamate, have been linked to schizophrenia. Finally, changes in the symptoms of schizophrenia don’t sync perfectly with changes in dopamine activity, there’s a long lag involved. It would be really cool to be able to tell you what really is going on in schizophrenia, but we’ll be waiting awhile for that–a full answer will probably require understanding mechanisms of belief, language, perception, and emotion, no small task.

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