Spaulding Motion Analysis Lab's Research Work in Nature's Scientific Reports Unravels How the Brain Generates Upper-limb Movements

(Boston, MA) - A research group based at the Motion Analysis Laboratory at Spaulding Rehabilitation Hospital has published a study entitled "Complex Upper-Limb Movements Are Generated by Combining Motor Primitives that Scale with the Movement Size" in Nature’s Scientific Reports. Researchers at Spaulding identified basic elements, referred to as motor primitives, that underlie the structure of movement patterns. The work done so far is primarily theoretical with a goal toward using the developed technique to analyze data collected during the performance of simple tasks, such as writing a word or drawing a circle. By breaking down movement to its most fundamental level the team has unraveled how complex movements are generated by humans. The team anticipates that ongoing studies leveraging this discovery will inform new rehabilitation intervention strategies.

Paolo Bonato, PhD, Director of the Spaulding Motion Analysis Lab, was as the senior author on the study led by Jose Garcia Vivas Miranda, PhD a visiting professor at Spaulding from the Universidade Federal da Bahia, Brazil. "In order to build interventions and approaches that can help people with upper-limb impairments, we need to have a thorough understanding of the components that underlie our ability to move. This study’s results provide a strong theoretical framework for us to build further research studies to look into complex upper-limb movements in our patients," said Dr. Bonato.

The team reported that motor primitives scale with the size of movement according to a power law. These results provide a novel key to the interpretation of brain and muscle synergy studies suggesting that human subjects use a scale-invariant encoding of movement patterns when performing upper-limb movements. This structure appears to be disrupted in patients undergoing rehabilitation. Restoring the physiological encoding of movement patterns is expected to lead to optimal clinical outcomes.

Subjects in the study were asked to perform a battery of motor tasks. They were instructed to sit at a table in a position such that the laboratory coordinate system was aligned with the anatomical planes. For all the tasks, reflective markers enabling movement tracking were placed on the subjects’ sternum and the back of the dominant hand. For tasks when a pen was used, an additional reflective marker was placed on the tip of the pen. Tracking of the reflective markers was achieved by using a camera-based motion capture system. The motor tasks included drawing different geometrical shapes, writing words in cursive and capital letters, performing goal-directed three-dimensional arm reaching movements, performing three-dimensional random arm movements, and performing one-dimensional arm movements (i.e. sliding the hand along a ruler) with and without targets.

The hand trajectory of motion during the performance of one-dimensional point-to-point movements has been shown to be marked by motor primitives with a bell-shaped velocity profile. Researchers have investigated if motor primitives with the same shape mark also complex upper-limb movements. They have done so by analyzing the magnitude of the hand trajectory velocity vector. This approach has failed to identify motor primitives with a bell-shaped velocity profile as the basic elements underlying the generation of complex upper-limb movements. This study examined upper-limb movements by analyzing instead the movement components defined according to a Cartesian coordinate system with axes oriented in the medio-lateral, antero-posterior, and vertical directions. To the researchers’ surprise, the results showed that a broad set of complex upper-limb movements can be modeled as a combination of motor primitives with a bell-shaped velocity profile along the axes of the above-defined coordinate system.

Individuals can visit http://srh-mal.net/ to learn more about the Motion Analysis Laboratory at Spaulding Rehabilitation Hospital.

About Spaulding Rehabilitation

A member of Partners HealthCare, Spaulding Rehabilitation includes Spaulding Rehabilitation Hospital, its main campus in Charlestown as well as Spaulding Rehabilitation Hospital Cape Cod, Spaulding Hospital Cambridge and Spaulding Nursing and Therapy Center Brighton, as well as twenty-five outpatient sites throughout Eastern Massachusetts. U.S. News & World Report has recently named Spaulding as the #2 rehabilitation hospital in the nation. Spaulding is one of the few hospitals in the U.S. to be awarded the prestigious Model Systems designation in all three areas of care—Spinal Cord Injury, Traumatic Brain Injury, and Burn Injury—selected by the National Institute on Disability, Independent Living and Rehabilitation Research. A teaching hospital of Harvard Medical School, Spaulding has been recognized by Doximity Residency Navigator as the top residency program in rehabilitation by reputation in the nation. Spaulding has been also recognized by the 2018 Disability Equality Index as a “Best Places to Work for Disability Inclusion”. For more information, please visit www.spauldingrehab.org.