Introduction
Great technological advances have been made to help address the structural and motor consequences of amputation, yet amputation also results in reductions and changes in somatosensation. The effects of these changes on motor planning remain largely unexplored. Sensation is an integral part of the creation, execution, and recognition of motor tasks. While motor planning is often thought of in a linear fashion -- inputs being integrated to produce a motor output -- the system is capable of producing multiple outputs based on available inputs. The motor planning system may be recruited to determine absent or deficient information based on the information that is available. For example, watching a person perform a motor action that interacts with an object involves recruitment of sensorimotor areas, and can lead to recognition of the goals of that task. Similarly, given a task goal along with visual and somatosensory information, the motor system creates motor plans to accomplish the goal.
Motor plans for object interactions are developed based on the structure of the object, the morphology of the hand, and prior interactions with similar objects. Radical changes in sensory availability, such as in amputation, can potentially lead to deficits that propagate throughout motor planning. Reduced availability of somatosensory feedback may lead to deficits in developing motor plans or recognizing the goals of actions performed by others. While these activities are still possible, they may involve compensatory neurobehavioral strategies that involve decreased efficiency, precision, and reliability, and increased cognitive demand due to recruitment of higher-level cortical systems. It is conceivable that all of these effects are present.
Just as motor planning is dependent upon somatosensory and visual information, execution of motor plans is reliant upon the integration of several streams of feedback, predominantly visual and somatosensory feedback. Brain regions recruited to perform the analysis and integration of feedback include premotor cortex for proprioceptive somatosensory feedback, and parietal cortex for visual feedback. While these areas are adept at dealing with delayed, noisy feedback, if the reliability of the sensory information is significantly reduced, sensory integration requires recruitment of higher cognitive areas such as the anterior frontal cortex.
While the amputee is presented with decreased and perhaps less reliable somatosensory information, they also must learn new ways to perform tasks and create appropriate motor plans. Thus, the challenges of sensory loss are compounded. Augmented somatosensory feedback may ameliorate deficits in motor planning and execution while reducing the need for compensatory neurobehavioral processes. Augmented feedback may be salient independent of location and modality, and may lead to its incorporation into motor planning and recognition. The goal of the proposed research is to determine the neurobehavioral effects of sensory reduction and augmented feedback on motor planning in upper-extremity tasks.
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