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Parkinson's disease does more than cause tremors and trouble walking. It can also affect sleep, smell, digestion and even thinking. NPR's Jon Hamilton reports on new research suggesting that's because the disease disrupts a brain network that links the mind and body.
JON HAMILTON, BYLINE: People with Parkinson's often have symptoms that are hard to explain, says Hesheng Liu of Changping Laboratory in Beijing. For example, he says patients may be able to walk most of the time but freeze up when a path becomes narrow or someone asks them a question.
HESHENG LIU: So you know that their movement problems is not simply related to their motor circuits. It's also related to their cognitive circuits.
HAMILTON: But it hasn't been clear why. Then several years ago, a team led by researchers at Washington University in Saint Louis discovered a brain network that seems to connect movement and thinking. They named it the somato-cognitive action network - or SCAN. And Liu's team thought it might explain some of the odd symptoms of Parkinson's. So they used MRI data on more than 800 brains to compare the SCAN networks in healthy people with those in people with Parkinson's.
LIU: In the patients, the connectivity in this SCAN network is abnormally high.
HAMILTON: The network linking thoughts and actions has too many connections. Liu says this causes signals to get stuck.
LIU: It almost feels like a tunnel is jammed, so no traffic can go normally.
HAMILTON: Next, Liu's team looked to see what happened to the SCAN network when people with Parkinson's got deep brain stimulation, a treatment that delivers pulses of electricity to areas affected by the disease.
LIU: When the stimulator is turned on, the connectivity was immediately lowered.
HAMILTON: Allowing brain traffic to flow normally again. Liu wanted to know how other treatments altered the SCAN network. So his team studied patients being treated with the drug levodopa, magnetic stimulation and focused ultrasound.
LIU: All these effective treatments are actually acting on this same circuitry, and the effect is remarkably identical.
HAMILTON: And treatments seemed to be more effective when they focused on areas that are part of the SCAN network. The research appears in the journal Nature. Peter Strick, a neurobiologist at the University of Pittsburgh, says it reflects a better scientific understanding of a disease that affects about 1 million Americans.
PETER STRICK: In the past, people thought of Parkinson's disease as the classic movement disorder. But it's clear now that multiple systems are involved in Parkinson's disease.
HAMILTON: Stick says patients often describe symptoms that go beyond tremor, slurred speech and a shuffling gait. These include chronic constipation, a reduced sense of smell, sleep disorders, memory lapses and fatigue, all of which involve brain systems with no direct link to voluntary movement. Strick recalls one man whose early symptoms included a drop in blood pressure when he stood up.
STRICK: He would fall down unexplainably, and people thought he was a drunk. There's such a stigma attached to that that when he was diagnosed with Parkinson's disease, he said, there, I'm not a drunk.
HAMILTON: Strick says the new study appears to explain symptoms like that. They occur because the SCAN network includes brain areas that control involuntary functions like heart rate, digestion and blood pressure.
STRICK: You don't say, well, OK, I'm going to stand up now, and so I've got to increase the blood flow in my brain. This is sort of the housekeeping that's taken care of for you.
HAMILTON: If your brain is healthy. Strick says current treatments for Parkinson's don't fix problems like that. But future ones might, he says, by targeting overlooked areas in the brain SCAN network.
Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.
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