Young adults can learn to predict unexpected posterior perturbations using an auditory cue

To reduce the effect of an expected postural perturbation, central nervous system uses anticipatory postural adjustments (APAs), which include the activation and inhibition of the postural muscles and a slight shift of the center-of-pressure (COP) position. The generation of APAs majorly relies on the availability of visual information, and is learned through past experience. Hence, such protective mechanism to maintain balance is not implemented when perturbation comes from one’s back unexpectedly. Our previous work showed that young adults could rely on an auditory cue only to generate APAs for a front perturbation similar to that when vision was available. So the purpose was to evaluate whether adults could learn to generate APAs for an external perturbation coming from the back relying only on an auditory cue

Older Adults Retain the Ability to Predict External Perturbations Using Auditory Cues Only

To maintain balance and prevent destabilization, humans utilize anticipatory postural adjustments (APAs) prior to the postural perturbations based on predictions and past experience. APAs involve the activation and inhibition of the trunk and leg muscles and a shift of the center-of-pressure (COP) position. The generation of APAs majorly relies on the availability and accuracy of visual information. However, our previous work showed that young adults could rely on an auditory cue only to generate APAs for an external perturbation similar to that when the visual information was available. Older adults generally have diminished APAs and consequently diminished postural control when postural perturbations occur. In this study, we aimed to train older adults to rely on an auditory cue to generate APAs in response to an external perturbation, and examine the retention of this learning effect after 1 week

The role of an auditory cue in generating anticipatory postural adjustments in response to an external perturbation

Anticipatory postural adjustments (APAs) are usually generated to minimize the potential postural disturbance induced by predictable external perturbations. Visual information about a perturbation is important for the generation of APAs, but whether people can rely on auditory information to generate APAs is unknown. The aim of this study was to investigate the role of an auditory cue in generating APAs when visual information is not available. Fifteen young adults participated in the study. They received external perturbations a) with visual information but no auditory information available, b) without neither visual nor auditory information, c) with both visual and auditory information available, and d) with only auditory information available. Electromyography (EMG) activities of eight leg and trunk muscles and displacements of the center_of-pressure (COP) were recorded and analyzed during the anticipatory and compensatory (CPAs) phases. Outcome measures included the latencies and integrals of muscle activities, COP displacements, and indices of co-contraction and reciprocal activation of muscles. The results showed that after a short training, participants were able to rely only on the auditory cue to generate APAs comparable to that when the visual information was available. In addition, a training efect was found such that the participants demonstrated stronger APAs and less demands for CPAs through the training trials. The outcome provides a foundation for future studies focusing on the utilization of auditory cues for postural control in older adults and individuals who have vision defcit

The Role of Predictability of Perturbation Magnitudes in Control of Posture

People frequently experience perturbations while standing in crowded areas or when interacting with external objects. Balance impairment is common in older adults with mild cognitive impairment (MCI). Balance maintenance in response to a perturbation is affected by predictability of magnitude of body disturbance. The purpose of the dissertation was to investigate postural control associated with exposures to perturbations of different magnitudes. In study 1, twenty young adults received pendulum perturbations of small or large magnitudes induced in sagittal plane. In study 2, twenty young adults received external perturbations induced in vertical plane by catching objects of small or large magnitudes. In study 3, ten young adults performed self-initiated perturbations induced by lifting either light or heavy objects. In study 4, twelve healthy older adults and twelve young adults received pendulum perturbations of small or large magnitudes and in study 5, fifteen individuals with MCI and fourteen age-matched control participants received pendulum perturbations of small or large magnitudes. All participants were not told about perturbation magnitudes, so they were exposed to a perturbation of either known magnitude (as such, predictable) in condition of repetitive magnitude or unknown magnitude (unpredictable) in condition of the unpredictable change of perturbation magnitude. Electromyographic activity of leg and trunk muscles and center of pressure (COP) displacements were recorded and analyzed during anticipatory (APAs) and compensatory (CPAs) phases of postural control. The outcomes of studies 1, 2 and 3 involving body perturbations induced by three different tasks showed similar trend revealing that when the perturbation magnitude suddenly changed, the participants tended to rely on prior experiences in dealing with perturbations and required less than six trials to adjust APAs and CPAs to new perturbation magnitude. The results of study 4 showed that smaller APAs in older adults were observed as compared to young adults in predictable conditions. Older adults also required more trials to optimize postural adjustments, as compared to young adults. The results of study 5 showed that individuals with MCI demonstrated smaller APAs in unpredictable conditions and required more trials to optimize postural adjustments, as compared to healthy older adults. The findings suggest that aging and cognitive decline adversely affect abilities to predict perturbation magnitude

Effect of predictability of the magnitude of a perturbation on anticipatory and compensatory postural adjustments

Balance maintenance in response to a perturbation could be affected by the predictability of the magnitude of the body disturbance. We investigated anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to perturbations of predictable and unpredictable magnitudes. Twenty young adults received series of perturbations of small or large magnitudes the order of which was varied. Electromyographic activity of six leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded. The muscle onset time, integrals of muscle activity, and COP displacements in the anterior–posterior direction were analyzed during the APA and CPA phases. The results indicated that when the participants were exposed to the repeated perturbation magnitude, it became predictable and they generated APAs more precisely according to the magnitudes of the perturbation. Moreover, when the magnitude of perturbation changed unpredictably, the participants overestimated or underestimated the magnitudes of the perturbation, as they generated APAs based on their prior experience of dealing with the perturbation. The optimal adjustment of APAs occurred after five trials of repeated perturbations. The findings imply that the process of APAs and CPAs generation depends on the accuracy of the predictability of perturbation magnitudes