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Rob Summers was 20 in the summer before his junior year at Oregon State University in 2006. A pitcher on the school's baseball team, he went out around midnight to get his gym bag out of his car when a hit-and-run driver jumped the curb, striking him and leaving him paralyzed with an injury to the spinal cord from C7-T1.

Today Summers can stand for several minutes and move his legs, feet, and toes. He has regained some bladder control and sexual functioning, as well as the ability to regulate his body temperature through mechanisms such as perspiration.

These gains are the result of unprecedented treatment -- begun in December 2009 -- using electrical stimulation of the spinal cord.

After 80 sessions of task-specific training, epidural stimulation from an implanted unit allowed Summers to stand, bearing all his weight, for up to 4.25 minutes, Susan Harkema, PhD, of the University of Louisville in Kentucky, V. Reggie Edgerton, PhD, of the University of California Los Angeles, and colleagues reported online in The Lancet.

Summers had previously undergone 26 months of locomotor training with assistance on a treadmill that had failed to produce any changes in electromyographic activity in the legs, the researchers explained.

"This unexpected recovery of supraspinally mediated movement suggests that activity-dependent mechanisms promoted plasticity of anxonal projections that presumably were spared by the injury," observed Grégoire Courtine, PhD, of the University of Zurich in Switzerland, and colleagues in a commentary accompanying the case report.

Animal studies had shown that the spinal cord is capable of generating motor commands without signals from the brain by means of neural networks known as central pattern generators.

In paralyzed humans, epidural stimulation has been shown to induce rhythmic movements of the legs while the patient lies supine.

Most [spinal cord injuries] involve a contusion or compressive injury of the cord that causes a great deal of damage, but leaves a certain number of nerve fibers that connect the brain with the spinal cord," Edward D. Hall, PhD, of the University of Kentucky and the Spinal Cord and Brain Injury Research Center in Lexington, observed in an email to ABC News and 番茄社区.

Harkema's team in Louisville had been doing research to see if spinal cord stimulation could activate neural circuits in the spine and, coupled with sensory input from the legs, permit standing and locomotion. Summers went to Louisville to see if they could help him.

In December of 2009, the team implanted a 16-electrode array over the young man's spinal segments L1-S1.

They also implanted a pulse generator connected to an electrode lead in the abdomen.

The researchers explained that, although Summers was paralyzed below the chest, he was classified as grade B on the American Spinal Injury Association's neurologic impairment scale since he had light touch sensation below the area of the spinal injury. But he had no voluntary control over the muscles of legs and trunk and no ability to contract the bladder.

The investigators tested various amplitudes ranging from 0.5 to 10 V and frequencies of 5 Hz to 40 Hz, in stimulation sessions ranging from 40 minutes to two hours.

Summers has reported tingling sensations at the site of the implanted electrode and in the muscles being activated, but did not experience pain during the stimulation sessions.

Initially, he was able to stand only with 65% body weight support, but over time he progressed to full weight bearing.

In addition to learning to stand unaided, Summers eventually progressed to the extent that he could stand up from a sitting position, which resulted in a marked increase in electromyographic activity.

He then learned task-specific sensory cues such as positioning of the legs, hips, and knees to accomplish step-like movements during 30 Hz to 40 Hz epidural stimulation.

But without the epidural stimulation, no electromyographic activity could be detected when his trainers assisted him in performing these stepping movements.

Hall cautioned that if this approach is shown to help in other patients, it may allow them to walk with the aid of a walker.

"While this will have value, it is important to note that it will not reproduce normal walking," Hall said.

If Summers isn't running around any baseball diamonds, he has a renewed sense of well being and self-esteem. Now 25, he lives in Los Angeles. And last summer, he spent 10 days helping at a baseball camp in Florida.

"One possible explanation for this recovery is that residual supraspinal connections that existed but could not be detected clinically were reactivated or that new supraspinal connections to the spinal networks were formed," Edgarton's group noted in their paper.

"Challenges lie ahead," stated Courtine and colleagues in their commentary and the findings need to be replicated in a clinical trial with sufficient numbers of patients.

Nonetheless, they wrote, "The exceptional results bring new hope in a field that has remained unsatisfying -- with limited progress despite decades of research throughout the world."

Naomi Kleitman, PhD, of the National Institutes of Health in Bethesda, Md., also found Summers' story hopeful. Most people are unaware of the complex circuits in their spine that transmit commands to the body from the brain, she told 番茄社区 and ABC News in an email.

"Spinal cord injuries break this vital connection but the sophisticated circuitry of the spinal cord remains, ready to coordinate stepping if it receives the right commands. Harnessing that potential has been the goal of decades of research to understand spinal cord function and to find effective ways to restore function after injury," Kleitman explained.

This article was developed in collaboration with ABC News.

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