Psychological Predictive Effects Of Sudden Postural Perturbation

Background:Postural control is a vital motor function and has been defined as the control of the body’s position in space for the purposes of balance and orientation. A postural perturbation is a sudden change in conditions that displaces the body posture away from equilibrium. In response to sudden posture perturbation, two different subconscious neural control strategies in central nervous system are used to coordinate sequential movements of postural and focal muscles, named anticipatory postural adjustments (AP As) and compensatory postural adjustments (CPAs). The subjective psychological expectation integrated from sensory information from visual, proprioceptive and vestibular systems by brain make postural control system response to the sudden perturbation timely and reasonable. In recent years, the studies of physiological and psychological mechanism of psychological predictive effect of sudden posture perturbation were hotspots in motor control research. Investigating and observing the characteristics of psychological predictive effect of postural disturbance helps to reveal the relationship between conscious perception and subconscious motor control. However, whether the change of subjective psychological prediction effect itself can influence the control strategies in CNS still lack experimental evidence.Objective:This study aimed to examine the psychological predictive effect of sudden posture perturbation magnitude on the APAs and CPAs by which CNS acts on focal muscles and lumbar posture muscles under internal, external, uncertainty and illusion conditions, which provides a theoretical basis for further improving control theories of neuromuscular cognitive neuroscience.Method:The classic arm-rising test, ball hitting test and bimanual load-lifting task were performed with surface electromyography (sEMG) and displacements of center of pressure (COP) signal analysis. In the Arm-raising test, participants rapidly raise arms with a load of 0kg/1kg/2kg in both hands. In the Ball-hitting test, participants caught a ball fell from eye level to the pan holding in their hands. In bimanual load-lifting task, a load of 1kg/2kg/3kg in one hand was lifted by themselves or experimenter. In uncertain condition, participants caught ball with different weight but same visual shape, and in illusion condition, participants caught ball with different visual shape but same weight. sEMG activities of focal muscle and posture muscle and data of body sway were recorded. The pre-action time, integrated EMG and COP displacement of APAs and CPAs were calculated to determine the effects of perturbation magnitude from different sources on APAs and CPAs of focal and postural muscles.Results:The posture perturbation magnitude had a psychological predictive effect on muscles under both internal and external perturbation conditions. In the Arm-rising test, the APAs IEMG of BB,LES and LMF significantly increased with the magnitude of perturbation, while the pre-action time and CPAs IEMG of all these muscles had no significant different under all 3 load levels. In the Ball-hitting test, the expectation of perturbation magnitude had significant effect on the pre-action time of both BB and LMF, as well as the APAs IEMG of BB, LES and LMF. But perturbation magnitude expectation had no effect on the CPAs IEMG on all 3 muscles. In the Load-lifting task, the posture perturbation magnitude had a psychological predictive effect on muscles under internal perturbation conditions. Under the internal perturbation condition, the APAs IEMG of BB,LES and LMF significantly increased with the magnitude of perturbation, while the pre-action time and CPAs IEMG of all these muscles had no significant different under all 3 load levels. Under the external condition, the expectation of perturbation magnitude had no significant effect on the pre-action time and APAs IEMG of BB, LES and LMF. Under the uncertain condition when the ball weight kept unknown using ball-hitting test, the uncertain psychological prediction had no significant effect on the pre-action time, IEMG of APAs and CPAs on lumbar muscles and the displacement of COP. Compared with the known condition, the pre-action time of LES and LMF, the IEMG of APAs and CPAs and the displacement of COP in both APAs and CPAs were significantly increased. Under the illusion condition, the pre-action time, the IEMG and COP of APAs and CPAs increased in the big ball level at first; but after repeating the difference of sEMG of lumbar posture muscles and displacement of COP between the two levels disappeared.Conclusion:We conclude that psychological predictive effects of posture perturbation are existed on both posture and focal muscle activities. Such effects are exhibited differently depending on internal or external perturbations. CNS will orchestrate to give an optimal control of posture muscle through adjustments of APAs IEMG under internal condition, or through adjustments of both pre-action time and APAs IEMG under external condition. The effects are also exhibited differently under known and unknown, or accurate and inaccurate conditions. CNS will orchestrate to give a maximum control of posture muscle through adjustments of both pre-action time and IEMG of APAs mechanism under unknown condition. CNS will orchestrate to give an optimal control of posture muscle under size-weight illusion conditions, which suggest the well learning effect of CNS’ posture control system in repeating postural perturbation task. The observed effects on APAs and CPAs suggest that the psychological predictive effect of sudden posture perturbation magnitude comes mainly from the CNS modulation on APAs mechanism.