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Five minutes was too much effort
The man who stopped
Until then he had been productive, well liked, and surrounded by friends. Then he turned indifferent to work and to people alike. An antidepressant changed nothing. He lost his job, and he was too apathetic to apply for Social Security, so friends took him in and regretted it almost at once. He sat in a chair all day waiting for them to cook and clean, and they had to prompt him to shower.
A London neurologist who saw him had to phone ahead to get him to the appointment, and he still showed up late, disheveled, with stains on his shirt. He wasn't unhappy at all. He had lost his apartment because he couldn't be bothered to pay the rent, and he was still looking forward to good things in life. Why not listen to music at home? Putting the system together would take time. How long? Five minutes.
Two tiny strokes
His scans showed two tiny strokes in the ventral striatum, part of the basal ganglia, an ancient structure that links motivation signals to action and is found in the lamprey, a vertebrate 360 million years old. Told to go take a shower, he would. Left alone, nothing set him in motion.
The turnaround
A drug that supplies a building block of dopamine made no difference. A second drug that stimulates dopamine receptors directly was tried next. Three months later the neurologist did not recognize the man in the waiting room. He had showered, had a haircut, wore a suit, had a new job, and had a new girlfriend.
How can two tiny strokes wipe out motivation?
The ventral striatum sits inside loops that carry signals from the frontal lobes down through the basal ganglia and thalamus and back up again. Signals from many brain regions converge on small areas along those loops, so damage the size of a pea can silence a circuit that spans much of the brain. Neurologists call a small stroke that disrupts a whole network a strategic infarct. Small strokes in the caudate nucleus, another part of the striatum, are also a recognized cause of abulia, a severe loss of will.
Why would one dopamine drug work when another failed?
A drug that supplies a building block of dopamine, such as levodopa, depends on neurons to convert it into dopamine and release it. A drug that stimulates dopamine receptors directly skips those steps and acts on the receiving cells themselves. Both classes are used in Parkinson's disease, where the neurons that make dopamine are lost over time.
Why do lampreys matter for human brain science?
Sten Grillner's group at the Karolinska Institute has shown that the lamprey's basal ganglia has the same pathways as the mammalian version. Those matching pathways suggest that the design dates back to the earliest vertebrates. Because the lamprey nervous system is small and easy to study, it has become a standard animal for tracing how the basal ganglia select one action over its competitors.
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