For the first time in humans, investigators at Cedars-Sinai have identified the neurons responsible for canceling planned behaviors or actions — a highly adaptive skill that when lost, can lead to unwanted movements.

Known as “stop signal neurons,” these neurons are critical in powering someone to stop or abort an action they have already put in process, according to Dr. Ueli Rutishauser, a professor of neurosurgery, neurology and biomedical sciences at Cedars-Sinai.

“We have all had the experience of sitting at a traffic stop and starting to press the gas pedal but then realizing that the light is still red and quickly pressing the brake again,” said Rutishauser , senior author of a study published online in the peer-reviewed journal Neuron. “This first-in-human study of its kind identifies the underlying brain process for stopping actions, which remains poorly understood.”

The findings, Rutishauser said, reveals that such neurons exist in an area of the brain called the subthalamic nucleus, which is a routine target for treating Parkinson’s disease with deep brain stimulation.

Patients with Parkinson’s, a motor system disorder affecting nearly 1 million people in the U.S., suffer simultaneously from both the inability to move and the inability to control excessive movements. The paradoxical mix of symptoms has long been attributed to disordered function in regions of the brain that regulate the initiation and halting of movements. How this process occurs and what regions of the brain are responsible have remained elusive to define despite years of intensive research.

Dr. Jim Gnadt, program director for the NIH Brain Research through Advancing Innovative Technologies Initiative, which funded the project, said the Cedars-Sinai study helps us understand how the human brain is wired to accomplish rapid movements.

“It is equally important for motor systems designed for quick, fast movements to have a `stop control’ available at a moment’s notice — like a cognitive change in plan — and also to keep the body still as one begins to think about moving but has yet to do so,” he said.

To make the discovery, the Cedars-Sinai research team studied patients with Parkinson’s who were undergoing brain surgery to implant a deep brain stimulator — a relatively common procedure to treat the condition. Electrodes were lowered into the basal ganglia, the part of the brain responsible for motor control, to precisely target the device while the patients were awake.

The researchers discovered that neurons in one part of the basal ganglia region — the subthalamic nucleus — indicated the need to `stop’ an already initiated action and responded very quickly after the appearance of the stop signal.

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