Reductions in body sway responses to a rhythmic support surface tilt perturbation can be caused by other mechanisms than prediction

Abstract

Studies investigating balance control often use external perturbations to probe the system. These perturbations can be administered as randomized, pseudo-randomized, or predictable sequences. As predictability of a given perturbation can affect balance performance, the way those perturbations are constructed may affect the results of the experiments. In the present study, we hypothesized that subjects are able to adapt to short, rhythmic support surface tilt stimuli, but not to long pseudorandom stimuli. 19 subjects were standing with eyes closed on a servo-controlled platform tilting about the ankle joint axis. Pre and post to the learning intervention, pseudo-random tilt sequences were applied. For the learning phase, a rhythmic and easy-to-memorize 8-s long sequence was applied 75 times, where subjects were instructed to stand as still as possible. Body kinematics were measured and whole body center of mass sway was analyzed. Results showed reduced sway and less forward lean of the body across the learning phase. The sway reductions were similar for stimulus and non-stimulus frequencies. Surprisingly, for the pseudo-random sequences, comparable changes were found from pre-to post-tests. In summary, results confirmed that considerable adaptations exist when exposing subjects to an 8-s long rhythmic perturbation. No indications of predictions of the learning tilt sequence were found, since similar changes were also observed in response to pseudo-random sequences. We conclude that changes in body sway responses following 75 repetitions of an 8-s long rhythmic tilt sequence are due to adaptations in the dynamics of the control mechanism (presumably stiffness).

Balance Adaptation While Standing on a Compliant Base Depends on the Current Sensory Condition in Healthy Young Adults

“…We had postulated that a process of postural adaptation would take place, also in the absence of reactions to external artificial stimulation(s), and reflect a progressive involvement of higher centres (Mierau et al, 2015;Kaulmann et al, 2020). We leveraged the use of the modulations in the frequency of the power spectrum of the CoP excursions (Schumann et al, 1995), following the approach exploited in several studies on balance adaptation to postural disturbance (Loughlin et al, 1996; Kiers et al, 2015;Borel and Ribot-Ciscar, 2016;Assländer et al, 2020). In accordance with our assumptions, we have seen that adaptation occurs during repeated, prolonged standing-on-foam trials.…”

“…On a very short time scale, post-effects of a particular sensory condition are observed on shifting to a different condition (Hay et al, 1996) or are produced by sensory reweighting after attenuation of one modality (Billot et al, 2013;Honeine and Schieppati, 2014), or simply modify postural adjustments after a single training session of a catching task (Kanekar and Aruin, 2015). What triggers adaptation, whether it is dependent on predictions of balance threats or on the capacity of reweighting the sensory information, or else on explicit learning is a matter of controversy (Peterka and Loughlin, 2004;Assländer et al, 2020;Bakker et al, 2021;see Rothwell et al, 2021, for an excellent short account of neural adaptation recourses). The present investigation claims to be a preliminary methodological approach to such a complex question.…”

Adaptation of balancing behaviour during continuous perturbations of stance. Supra-postural visual tasks and platform translation frequency modulate adaptation rate

“…During periodic translations of the support base, a certain time interval elapses from the trial onset until a steady-state of head and body oscillation is reached [3,[28][29][30][31][32]. This may account for changes in balance control dynamics depending on explicit predictions of the sequence of perturbation cycles [33].…”

Acute and chronic changes in postural control in response to different physiological states and external environmental conditions

“…We had postulated that a process of postural adaptation would take place, also in the absence of reactions to external artificial stimulation(s), and reflect a progressive involvement of higher centres (Mierau et al, 2015;Kaulmann et al, 2020). We leveraged the use of the modulations in the frequency of the power spectrum of the CoP excursions (Schumann et al, 1995), following the approach exploited in several studies on balance adaptation to postural disturbance (Loughlin et al, 1996; Borel and Ribot-Ciscar, 2016;Assländer et al, 2020). In accordance with our assumptions, we have seen that adaptation occurs during repeated, prolonged standing-on-foam trials.…”