Evaluation of the Complexity of Control of Simple Linear Hand Movements Using Principal Component Analysis

In tests on 10 healthy men, we recorded EMGs related to the performance of simple (with one degree of freedom) linear movements of the right hand; straight movement trajectories lay within the parafrontal planes, and principal component analysis (PCA) was used for the evaluation of complexity of the central control of such movements. The first principal component was discriminated from EMG activity of eight muscles involved in the movements, and the magnitude of this component was associated with complexity of the central control of the performed movement. As was believed, the control of the task performance by the CNS was more complex when the size of the first principal component was smaller. It was found that the complexity of the central control was significantly smaller for the movements performed within a proximal operational zone and gradually increased for more distal trajectories. With respect to the central control, the movements provided by cyclic contraction and elongation of the extensor muscles were simpler. Hysteresis of the muscle contractions exerted ambiguous effects on the complexity of the control. It is known from skeletal and muscular anatomy that even mechanically simple movements may have different complexities at the level of the musculoskeletal system, which is taken into account by the central nervous system when performing these movements. This raises the problem of creating methods for assessing the complexity with which the CNS collides with the realization of motor tasks.