If you have ever hit your stride on a moving walkway, the type commonly found in airports, consider how it felt when you stepped back onto solid ground. You may have felt a sudden but brief discombobulation while your brain worked to correct its temporary mismatch with your body’s sense of movement. Laura Prosser, PhD, PT, is trying to induce a similar reaction to rehabilitate children after stroke.
As a research scientist in the Division of Rehabilitation Medicine at The Children’s Hospital of Philadelphia, Dr. Prosser’s work is focused on how the brain and its connection to the body change after damage and during rehabilitation. Her focus on children addresses an under-researched area in rehabilitation.
“Understanding how rehabilitation can impact neuroplasticity is the most exciting aspect of this research to me,” Dr. Prosser said. “Not much of this work has been done in children. At CHOP we are in a unique position to understand how the brains of children respond differently to rehabilitation than the brains of adults who have had an injury.”
Dr. Prosser is now conducting a small pilot study testing physical therapy outcomes after pediatric stroke using high-tech tools including a split-belt treadmill and brain-stimulating technology called transcranial magnetic stimulation (TMS). She aims to learn which approaches seem most promising to pursue in future larger trials.
The split-belt treadmill is exactly what it sounds like: Instead of a single moving belt underfoot, under each foot there is a separate belt moving at its own speed. Imagine if you were walking with only one foot on the airport’s moving walkway and the other foot on the floor, forcing each leg to move at a different pace — it might feel strange at first, but Dr. Prosser said, healthy brains tend to adjust to the asymmetric motion quickly, and injured ones only slightly less so.
Using this treadmill for rehabilitation, physical therapists calibrate the speed of each belt separately according to the individual patient’s gait pattern. After a stroke, individuals often experience hemiplegia, which is difficulty moving one side of the body, and results in an asymmetric walking pattern. But instead of using the treadmill for children to practice walking with a corrected, more-symmetrical gait, the treadmill belts’ speeds are set to make the error worse.
“The idea with error augmentation therapy is to exaggerate the error and force the brain to perceive asymmetry in movement, which it has become accustomed to,” Dr. Prosser said. “The brain responds by working harder to correct this newly recognized asymmetry.”
In her study, half of participants are randomized to receive 24 sessions of this asymmetrical gait training, while the other half of participants receive standard rehabilitation for their injury.
The next trick is to try to understand neurological changes over the course of treatment. TMS is a method that uses a magnetic field over the surface of the head to direct a pulse to a targeted area of the brain. In brain-injury studies like Dr. Prosser’s, TMS is a tool to measure the strength of the brain’s connection to muscle groups in the body.
Sudha K. Kessler, MD, neurologist and director of the Transcranial Magnetic Stimulation Lab at CHOP, delivers each study participant TMS pulses to activate their weakened leg muscles from the injured side of the brain, and on the opposite side to get a comparison. The timing and strength of the muscle response is an indicator of the quality of the brain/body connection. The researchers are tracking these responses over time to measure potential improvements with therapy.
“We are among just a few people who are trying to understand the pathways to the leg muscles in children,” Dr. Prosser said. “More commonly, people are studying the pathways to the upper extremity muscles because based on the anatomy of the brain, those cortical areas are much easier to access with this type of technology.”
Dr. Prosser and Dr. Kessler are also considering the potential of TMS and other noninvasive cortical modulating treatments as an aid to rehabilitation, not just as measurement tools. For example, a repetitive TMS program delivered immediately prior to physical therapy may help prime the brain for learning, improving the effectiveness of rehabilitation sessions.
“One of the things we’re finding so far with the TMS data is that we’re seeing many different patterns of cortical mapping in the children,” Dr. Prosser said. “In adults, cortical remapping after a stroke is more predictable.”
The finding suggests brain-based treatments for children may need to be more individualized. Genetic data may inform those individual treatments in the future, too. As part of the pilot study, Dr. Prosser’s team is collecting blood samples from participants to determine the presence of two particular genetic polymorphisms related to neuroplastic potential. When these variants are present in adults who have had a stroke, they are associated with more severe outcomes. How these gene variants may interact with ongoing brain-development processes in children, and the potential associations between these genes and response to rehabilitation, are unknown.
The small pilot study is being conducted with Rebecca Ichord, MD, director of CHOP’s Pediatric Stroke Program, and Heather Atkinson, PT, NCS, clinical specialist in the Pediatric Stroke Program. Enrollment has nearly reached its target of 12 patients. When complete, Dr. Prosser will examine results from the TMS, genetic biomarker, and physical therapy outcomes data to see which interventions may benefit from further testing in a larger clinical trial — taking the process of pediatric stroke rehabilitation one step forward at a time.