An electric stimulator, placed twice daily on a patient’s neck, could end up providing effective treatment for moderate traumatic brain injury — a disorder that currently has no proven treatment.

Researchers at Hennepin County Medical Center and the University of Minnesota are studying this experimental approach to stimulating the vagus nerve — a neurotransmitter that has been linked to depression and sleep problems — without the need for a device to be surgically implanted.

Two patients who suffered moderate brain injuries have already consented to the study, which is the first in the U.S. to explore noninvasive stimulation of the somewhat mysterious vagus nerve.

“To be honest, it’s not 100 percent understood,” said Dr. Uzma Samadani, head of HCMC’s brain research lab. “People have shown it affects neurotransmitter releases in particular areas of the brain that are important for recovery from functional loss. It also relieves some depression and it helps in restoring the sleep wave cycle.”

Depression and poor sleep are among the symptoms following traumatic brain injuries (TBIs); those severe enough to qualify for the HCMC study produce internal bleeding that shows up on brain scans. A Minneapolis man consented to the 12-week experiment after slipping on ice and hitting his head. Fifty patients will be enrolled by study’s end.

Implanted vagus stimulators are federally approved for epilepsy and treatment-resistant depression. An external device has been approved in Europe only for migraines.

“It’s a little better because its safer,” Samadani said of the external device. “You don’t have to worry about any surgical or device complications.”

An external device also holds the promise of treatment without drugs and their occasional side effects.

HCMC has several studies underway to detect and treat brain injuries. A larger study funded in part by Chicago-based Abbott is developing a reliable scheme to classify TBI severity. Studies in the coming months might focus on the use of hyperbaric oxygen and diets heavy in tryptophan (known for its sedating effects after turkey feasts at Thanksgiving).

Samadani planned to launch the device study in New York in 2012, when Hurricane Sandy closed the Manhattan VA Medical Center where she worked. She moved to HCMC in 2015.