Representation of a hand action in typically developed people and a foot action in people with dysplasia. A network in frontal and parietal areas, which is shown in yellow-orange, prefers a certain type of action, regardless of the acting body part. Photo credit: Yuqi Liu, PhD

People born with no upper limbs and reaching for an object with their feet engage the same area of ​​the brain where people reach for something with their hands, neuroscientists at Georgetown University Medical Center report.

The finding, which was published in PNAS on October 26, 2020, expands the fundamentals of the organization and function of the brain and offers potential future clinical advances, including the improvement of limb prostheses, says the study’s lead researcher, Assistant Professor Ella Striem-Amit, Ph .D. He heads the Sensory and Motor Plasticity Laboratory in the Neuroscience Department in Georgetown.

The new study suggests that the brain processes movement commands not just by controlling finely tuned muscle contractions, but also through higher-level motor areas that provide a blueprint for performing more complex motor functions such as reaching and grasping, whether they’re fingers acts or toes are used.

Evidence of these areas, which form the blueprint for finely tuned measures, emerged from the investigation of two groups. One consisted of four people with dysplasia (people born without arms or hands) who reached for or grabbed an object with their toes. The other is a control group of volunteers who used their hands first and then their toes to reach and grab. In all of these different situations, participants activated the same areas of the brain that are selective for accessibility, as well as the primary motor cortex that controls the muscles in the hands and feet.

“The study shows that some areas within the motor system evolve to compute a complex action or task, such as reaching and grasping. These actions do not depend on a person’s motor experience. So use an arm or a leg to reach an object illuminates the same areas on fMRI scans, “she says. “This is more abstract than the way the brain controls the fine-grained flexion of a particular part of the body, such as a limb. For example, fine-tuning an arm corresponds to one area in the central nervous system and controlling a leg to another area. This is point-to-point -Point organization. “

“We are building a model that shows that the computation for certain tasks such as reaching and sensing is a higher level of functionality, different from and independent of the subordinate action function, such as using an arm. We believe this is an organization general principle of brain design, “says Dr. Yuqi Liu, postdoctoral fellow at Striem-Amit’s SAMP Lab. Other co-authors are Alfonso Caramazza, Ph.D. from Harvard University and Gilles Vannuscorps, Ph.D., from Université catholique de Louvain.

Striem-Amit says this work, examining people born without hands, complements her and other groups’ previous findings on people born deaf or blind.

Previous studies have found that the higher-order visual and auditory cortex perform certain tasks regardless of sensory modality. For example, a visual association area is selective for letters, regardless of whether they are presented to typical controls visually or via braille or a sensory substitution device for congenitally blind persons. A higher-order auditory area processes temporal rhythms both when controls were presented with auditory sequences and visual sequences were presented to congenitally deaf persons.

“Similarly, in our study, the motor areas of the associations are selective for the type of action regardless of the specific body part,” says Striem-Amit. “One thing that the higher-order visual, auditory and motor areas have in common is that they seem to be organized functionally and independently of certain sensorimotor parameters.”

The results could be applied to the development of improved limb prostheses, says Striem-Amit. Current prostheses work by having their user dictate the coordinated movement parameters of the prosthesis at a low level, which is very complex and arduous. What could help is using the higher level command, she explains.

Striem-Amit adds, “If, in the long run, we better understand the representations of action at a higher command level, we may be able to perform prostheses not only with hand movement, but also at a higher action target level, which could result in less rejection of prostheses.”

Getting a grip on the organization of the brain: Studies have found that even those born without hands have an overlap between hand tools

More information:
Yuqi Liu el al., “Evidence of an effector-independent system of action in people born without hands”, PNAS (2020). Provided by Georgetown University Medical Center

Quote: The study of reaching and grasping with hand or foot reveals new knowledge about the brain (2020, October 26th), which was published on October 26th, 2020 at reveals-brain-insights.html

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