“Postural control and emotions – are center of pressure parameters affected by emotional imagery in healthy individuals?”

Abstract

Background and aim The relationship between postural control and emotions is intricately intertwined in our behaviors (e.g., stiffening strategies when exposed to threat). However, it is very complex and largely unexplored. A potential way to elucidate the effects of emotions on postural control is through script-driven emotional imagery, which is known to be a valid and reliable way to induce emotions. As it has not yet been used in the research field of postural control we aimed to examine the effect of script-driven emotional imagery on center of pressure (CoP) in healthy individuals.

Methods Participants listened to four emotional imagery scripts by means of stories exposed through headphones. The first was a neutral script, the other three were designed to induce emotions of acceptance, hostile-resistance, and relaxation. The subjects were instructed to imagine the stories as vividly as possible while standing upright on a foam pad with their eyes closed and arms hanging next to their body in a darkened room. Each emotional imagery script consisted of a baseline, imagery, and recovery phase. After each script, the subjects rated valence (pleasant to unpleasant), arousal (excited to calm), and dominance (dominated to in control) with the Self-Assessment Manikin (SAM) to check whether emotion induction was successful. Postural control was quantified by various CoP parameters: mean sway and standard deviation of sway, total sway, and sway velocity in both anteroposterior direction (AP) and mediolateral direction (ML), as well as the 95% confidence interval of the total sway area. Effects of the emotional imagery scripts on CoP and whether or not the emotions were successfully induced were analyzed using a mixed model. For CoP, the mixed model was based on difference scores between the baseline and imagery phases of each script.

Results Based on the SAM, the scripts successfully induced the intended emotions, as participants felt less pleasant (p< 0.0001), more aroused (p< 0.0001), and less in control (p< 0.0001) during the hostile-resistance script compared to the acceptance and relaxation scripts and during the acceptance script compared to the relaxation script. However, with an exception for mean CoP sway AP, which was smaller during the relaxation script in comparison to the acceptance script (p= 0.04), none of the scripts revealed any effect on CoP variables.

Conclusion Although script-driven emotional imagery was successfully induced in healthy individuals, the scripts minimally affected postural control. These findings may suggest that healthy individuals adopt flexible compensation strategies (both postural and emotional) to successfully adjust for induced perturbations.