Does the impaired postural control in Parkinson's disease affect the habituation to non-sequential external perturbation trials?

Anticipatory Postural Adjustments and Compensatory Postural Responses to Multidirectional Perturbations—Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation in Parkinson’s Disease

“…For instance, to change from the forward perturbation direction to the left direction, subjects had to turn 90° to the right ( Figure 1 ). Four trials were performed for each direction in a randomized order to minimize the influence of fatigue and habituation [ 63 , 66 , 68 ]. The subjects were instructed to stand on the force plate in a bipedal stance while barefoot, with an upright posture, keeping the knees straightened but not locked, both arms hanging down loosely, and directing their gaze ahead.…”

“…Muscle activity was quantified by the root mean square (RMS) and normalized to the maximum amplitude for each trial on the same muscle and subject [ 93 , 94 ]. Additionally, the co-contraction ratio, which is a measure of inter-muscle coordination and joint stiffness, was calculated as the percentage between the GM and TA using the mean of the normalized EMG data [ 66 , 78 , 95 , 96 ].…”

“…A more objective, reliable, and specific analysis can be achieved with standardized balance perturbations in conjunction with electromyography (EMG) and force plates to quantify muscle activation and body sway. Various studies have used computerized perturbations, such as platform translations [ 12 , 14 , 60 , 63 , 65 , 66 ], rotations [ 67 , 68 , 69 ], or standardized body pulls [ 34 ], to identify Parkinson’s subtypes or for diagnostic purposes including characterizing postural instability compared to healthy subjects. To summarize those study results, PD patients showed inflexibility in controlling muscle activity, including abnormal APA, impaired postural reflexes, and increased agonistic muscle activation with excessive antagonistic co-contractions [ 65 , 66 , 67 ].…”

“…Various studies have used computerized perturbations, such as platform translations [ 12 , 14 , 60 , 63 , 65 , 66 ], rotations [ 67 , 68 , 69 ], or standardized body pulls [ 34 ], to identify Parkinson’s subtypes or for diagnostic purposes including characterizing postural instability compared to healthy subjects. To summarize those study results, PD patients showed inflexibility in controlling muscle activity, including abnormal APA, impaired postural reflexes, and increased agonistic muscle activation with excessive antagonistic co-contractions [ 65 , 66 , 67 ]. Moreover, patients had difficulties in quickly adapting postural muscle synergies to different perturbation directions, which led to greater sway displacements and longer recovery times [ 12 , 14 , 37 , 65 , 66 , 67 , 70 , 71 ].…”

“…To summarize those study results, PD patients showed inflexibility in controlling muscle activity, including abnormal APA, impaired postural reflexes, and increased agonistic muscle activation with excessive antagonistic co-contractions [ 65 , 66 , 67 ]. Moreover, patients had difficulties in quickly adapting postural muscle synergies to different perturbation directions, which led to greater sway displacements and longer recovery times [ 12 , 14 , 37 , 65 , 66 , 67 , 70 , 71 ]. However, therapy-induced effects of anti-parkinsonian medication alone and in conjunction with STN-DBS on postural control, such as APA and CPR, have rarely been investigated or compared using such computerized methods.…”