Motor imagery modulation of body sway is task-dependent and relies on imagery ability

Abstract

In this study we investigate to what extent the effects of motor imagery on postural sway are constrained by movement features and the subject's imagery ability. Twenty-three subjects were asked to imagine three movements using the kinesthetic modality: rising on tiptoes, whole-body forward reaching, and whole-body lateral reaching. After each task, subjects reported the level of imagery vividness and were subsequently grouped into a HIGH group (scores ≥3, “moderately intense” imagery) or a LOW group (scores ≤2, “mildly intense” imagery). An eyes closed trial was used as a control task. Center of gravity (COG) coordinates were collected, along with surface EMG of the deltoid (medial and anterior portion) and lateral gastrocnemius muscles. COG variability was quantified as the amount of fluctuations in position and velocity in the forward-backward and lateral directions. Changes in COG variability during motor imagery were observed only for the HIGH group. COG variability in the forward-backward direction was increased during the rising on tiptoes imagery, compared with the control task (p = 0.01) and the lateral reaching imagery (p = 0.02). Conversely, COG variability in the lateral direction was higher in rising on tiptoes and lateral reaching imagery than during the control task (p < 0.01); in addition, COG variability was higher during the lateral reaching imagery than in the forward reaching imagery (p = 0.02). EMG analysis revealed no effects of group (p > 0.08) or task (p > 0.46) for any of the tested muscles. In summary, motor imagery influences body sway dynamics in a task-dependent manner, and relies on the subject' imagery ability.

Effect of Cervical Kinesthetic Motor Imagery on Postural Control of Healthy Young Adults with Fear of Falling

“…Fear has shown influence on the ability to perform gait MI [41]. Studies have shown that kinesthetic MI presents a modulation effect on orthostatic postural control [7][8][9], depending on the vividness of the imagined movement [10], corroborating our results, since the participants also presented high levels of vividness (KVIQ). The present study also showed that the FoF during the tasks of kinesthetic MI (cervical flexion and inclination) is able to modulate the CoP variables, increasing their oscillation, which indicates greater postural imbalance (Figure 2A,B).…”

“…For example, when an individual performs and imagines walking at a fixed distance, the time spent is similar, with no statistical difference [40]. Similarly, the number of repetitions of the same executed and imagined task in a "fixed time window" also presents no statistical difference [7,9,10]. Although the sample (n = 20) also has shown similarity between the execution and imagination of the tasks (cervical flexion and inclination) when comparing the number of repetitions (principle of isochronia), this same similarity was not observed when comparing the sensation of FoF between execution and imagination, indicating that the MI induces a greater modulation in the sensation of FoF in relation to the execution of the same tasks (see Figure 1).…”

“…No instructions were given on the frequency and speed of the executed or imagined movements. In the execution block, the experimenter counted the number of repetitions, and during the imaging block, the participant was instructed to mentally count the number of repetitions in each task [7,10]. At the end of each task in both blocks (execution and imagination) a question was asked about the FoF: "from zero to 100, how much did you feel afraid of falling?"…”

“…Although there is a common neural substrate between these two strategies [2,5], distinct neural circuits are accessed in each one of them by imagining the same task [3,6]. Studies have shown that kinesthetic MI presents a greater modulation in orthostatic postural control compared to visual MI [7][8][9], and this effect has been related to the level of vividness of the imagined movement [10].…”

Motor imagery and its effect on complex regional pain syndrome: an integrative review

“… 2 , 9 So far, the work done with CRPS using the MI has not taken into account these two types of strategies (Supplementary Tables S1-3) and it may exist different effects between them. For example, it has been shown that the MI kinesthetic has greater sway center of pressure (CoP) compared with the visual MI in different tasks 35-37 and this effect has been correlated with the intensity of the imagined movement, 38 which is another point that has not been explored in studies with CRPS-1. Therefore, it can be expected that MI strategies (visual and kinesthetic) may also have different effects on pain perception in the CRPS-1 reorganization.…”