Affect Balance Control Research Articles

Chronic ultra-mild stress improves locomotor performance of B6D2F1 mice in a motor risk situation

Chronic low grade stress predispose to psychopathological disorders. We consistently showed that chronic ultra-mild stress (CUMS) applied to B6D2F1 female mice induced behavioral disinhibition in several conflict exploration models. Insufficient reactivity to conflicts may be maladaptive and lead to inappropriate appreciation of potential risks and impaired ability to cope with those. Therefore, the purpose of the study was to assess the effect of a CUMS procedure on the behavior of mice in a motor risk situation based on multisensory conflict. Following three weeks exposure to various mild stressors, stressed and control B6D2F1 mice were tested on the rotating beam to determine how CUMS exposure affected balance control, posture stability and locomotor performance in response to a sensory–motor challenge. Detailed behavioral analysis included several parameters, both postural (height of the trunk, tail angle, number of imbalances, falls and head movements) and kinetic (mean velocity on the beam, distance covered with large and small movements, plus time spent in no-motion episodes). Comparisons between control and stressed mice showed that CUMS exposure increased mean velocity and improved locomotor performance in the learning task. In addition, sensitivity to sensory conflict seemed to be reduced in stressed mice, which displayed fewer behavioral adjustments to the increasing difficulty of the test compared to control mice. The results are discussed in terms of the possible influence of disturbances in behavioral and attentional inhibitory processes following CUMS exposure. Whether longer periods of CUMS exposure would shift the performance on the RTB from improvement to deterioration remain to be established.

Mood states and anxiety influence abilities to maintain balance control in healthy human subjects

Previous studies have shown that anxiety and balance disorders could be related; however, the association between psychological processes and equilibrium remains ambiguous. In this study, we have examined whether mood states and anxiety may influence the ability to use the somatosensory, visual and vestibular systems and affect balance control in healthy subjects. Seven male students were submitted to a program testing equilibrium over a 12-day period, during which moods and anxiety states were assessed using self-evaluated questionnaires. Significant negative correlations were found between moods, including anxiety, and the subject's sensory and motor systems of balance control, suggesting that low moods may alter balance performance. However, depending on the type of mood, it is likely that adverse changes in mood states may affect balance in different ways, either through the sensory organization or motor control.

Vestibulopathy and Age Effects on Head Stability During Chair Rise

It is unknown how vestibular dysfunction and age differentially affect balance control during functional activities. The objective of this study was to gain insight into the effects of age and vestibulopathy on head control when rising from a chair. Head relative to trunk (head-on-trunk) sagittal plane angular and linear control strategies were studied in patients with bilateral vestibular hypofunction (BVH) and in healthy subjects aged 30-80 years. A two-way analysis of variance was used to compare head-on-trunk kinematics by age (young vs elderly) and diagnosis (healthy vs BVH) at the time of liftoff from the seat. Angular control strategies differed with age but not diagnosis: young (healthy and BVH) subjects stabilized head rotations in space while elderly (healthy and BVH) subjects stabilized head rotations on the trunk. In contrast, linear control strategies differed by diagnosis but not age: BVH subjects (young and old) allowed a greater rate of head-on-trunk translation while healthy subjects (young and old) inhibited such translations. Young BVH subjects stabilized head-in-space rotations (as did young healthy subjects) without a functioning vestibular system, suggesting cervicocollic reflex and:or other sensory compensation for vestibular loss. Elderly BVH subjects stabilized head rotation with respect to the trunk, as did healthy elders, but did not stabilize head-on-trunk translations, suggesting a reliance on passive mechanical responses of the neck to sense head movements. We conclude that compensation strategies used by patients with vestibulopathy are age-dependent and appear to be more tractable in the younger BVH patient.

A model for the relation between the displacement of the ankle and the center of pressure in the frontal plane, during one-leg stance

We present and validate a model for the relation between the horizontal, frontal plane displacement of the ankle, representing frontal plane foot tilt, and the frontal plane displacement of the Center of Pressure (CoP) during one-leg stance. It is concluded that the frontal plane movements of the CoP should be regarded not as a measure of body sway, as is often done, but as a measure for the tilting movements of the foot as a mechanism for balance control. Foot breadth affects the gain of this mechanism in terms of CoP displacement and can potentially affect balance control.

Effectiveness of intrathecal baclofen on reducing lower extremity spasticity

Although balance during quiet standing is postulated to be influenced by multiple factors, including ankle stiffness, it is unclear how different mechanisms underlying increases in stiffness affect balance control. Accordingly, this study examined the influence of muscle activation and passive ankle stiffness increases on the magnitude and frequency of postural sway. Sixteen young adults participated in six quiet stance conditions including: relaxed standing, four muscle active conditions (10%, 20%, 30% and 40% maximum voluntary contraction (MVC)), and one passive condition wearing an ankle foot orthotic (AFO). Kinetics were collected from a force plate, while whole-body kinematics were collected with a 12-sensor motion capture system. Bilateral electromyographic signals were recorded from the tibialis anterior and medial gastrocnemius muscles. Quiet stance sway amplitude (range and root mean square) and frequency (mean frequency and velocity) in the sagittal plane were calculated from time-varying centre of gravity (COG) and centre of pressure (COP) data. Compared to the relaxed standing condition, metrics of sway amplitude were significantly increased (between 37.5 and 63.2%) at muscle activation levels of 30% and 40% MVC. Similarly, frequency measures increased between 30.5 and 154.2% in the 20–40% MVC conditions. In contrast, passive ankle stiffness, induced through the AFO, significantly decreased sway amplitude (by 23–26%), decreased COG velocity by 13.8%, and increased mean COP frequency by 24.9%. These results demonstrate that active co-contraction of ankle musculature (common in Parkinson’s Disease patients) may have differential effects on quiet stance balance control compared to the use of an ankle foot orthotic (common for those recovering from stroke).