Pushing Induced Sliding Perturbation Affects Postural Responses to Maintain Balance Standing

Abstract1. The relation between the social behavior and the electrical emissions of Gymnotus carapo is examined. 2. Members of the species Gymnotus carapo approach certain sources of electrical stimuli and, in a statistically significant number of instances, assume a stance parallel to the plane from which the stimuli originate. 3. The approach and postural responses elicited by electrical cues resemble those observed when two fish, placed in the same tank, interact socially. 4. Electrical cues therefore appear to facilitate certain social interactions in Gymnotus carapo. 5. The character of electrical emission in Gymnotus carapo appears to change as a function of certain social interaction: a. Interaction resembling aggression is accompanied by brief increases in the frequency of emission. b. The increases in frequency appear to be linked to thrusting movements. c. Fish interacting with one another appear to lock into a common frequency more often than fish that are not in physical contact with one another. d. During social interaction, one of the two fish is occasionally observed to halt emissions altogether. 6. The exact significance of the social behavior observed in the context of the life history of Gymnotus carapo is unknown.

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First trial and StartReact effects induced by balance perturbations to upright stance

Journal of Neurophysiology ◽

10.1152/jn.00766.2012 ◽

2013 ◽

Vol 110 (9) ◽

pp. 2236-2245 ◽

Cited By ~ 33

Author(s):

A. D. Campbell ◽

J. W. Squair ◽

R. Chua ◽

J. T. Inglis ◽

M. G. Carpenter

Keyword(s):

Startle Response ◽

Support Surface ◽

Wrist Movement ◽

Repeated Presentation ◽

Trial Effect ◽

Acoustic Stimuli ◽

Postural Responses ◽

Startreact Effect ◽

Startling Stimulus ◽

Repeated Test

Postural responses (PR) to a balance perturbation differ between the first and subsequent perturbations. One explanation for this first trial effect is that perturbations act as startling stimuli that initiate a generalized startle response (GSR) as well as the PR. Startling stimuli, such as startling acoustic stimuli (SAS), are known to elicit GSRs, as well as a StartReact effect, in which prepared movements are initiated earlier by a startling stimulus. In this study, a StartReact effect paradigm was used to determine if balance perturbations can also act as startle stimuli. Subjects completed two blocks of simple reaction time trials involving wrist extension to a visual imperative stimulus (IS). Each block included 15 CONTROL trials that involved a warning cue and subsequent IS, followed by 10 repeated TEST trials, where either a SAS (TESTSAS) or a toes-up support-surface rotation (TESTPERT) was presented coincident with the IS. StartReact effects were observed during the first trial in both TESTSAS and TESTPERT conditions as evidenced by significantly earlier wrist movement and muscle onsets compared with CONTROL. Likewise, StartReact effects were observed in all repeated TESTSAS and TESTPERT trials. In contrast, GSRs in sternocleidomastoid and PRs were large in the first trial, but significantly attenuated over repeated presentation of the TESTPERT trials. Results suggest that balance perturbations can act as startling stimuli. Thus first trial effects are likely PRs which are superimposed with a GSR that is initially large, but habituates over time with repeated exposure to the startling influence of the balance perturbation.

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Postural Responses to Sudden Horizontal Perturbations in Tai Chi Practitioners

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18052692 ◽

2021 ◽

Vol 18 (5) ◽

pp. 2692

Author(s):

Jernej Sever ◽

Jan Babič ◽

Žiga Kozinc ◽

Nejc Šarabon

Keyword(s):

Tai Chi ◽

Center Of Pressure ◽

Well Being ◽

Vertical Movement ◽

Control Group ◽

Age Difference ◽

Positive Effects ◽

Postural Responses ◽

Force Increase ◽

Load Release

Tai Chi has been shown to elicit numerous positive effects on health and well-being. In this study, we examined reactive postural control after sudden unloading horizontal perturbations, which resembled situations encountered during Tai Chi. The study involved 20 participants, 10 in the Tai Chi group (age: 37.4 ± 7.8 years), who had been regularly training the push-hand technique for at least 7 years, and 10 in the control group, consisting of healthy adults (age: 28.8 ± 5.0). Perturbations were applied at three different positions (hips, shoulders, and arms) via the load-release paradigm. Twenty measurements were carried out for each perturbation position. We measured peak vertical and horizontal forces on the ground (expressed percentage of body mass (%BM)), peak center of pressure displacement and peak horizontal and vertical velocities at the knee, hip and shoulder joints. The Tai Chi group exhibited smaller increases in vertical ground reaction forces when perturbations were applied at the hips (11.5 ± 2.1 vs. 19.6 ± 5.5 %BW; p = 0.002) and the arms (14.1 ± 4.2 vs. 23.2 ± 8.4 %BW; p = 0.005). They also responded with higher horizontal force increase after hip perturbation (16.2 ± 3.2 vs. 13.1 ± 2.5 %BW; p < 0.001). Similar findings were found when observing various outcomes related to velocities of vertical movement. The Tai Chi group also showed lower speeds of backward movement of the knee (p = 0.005–0.009) after hip (0.49 ± 0.13 vs. 0.85 ± 0.14 m/s; p = 0.005) and arm perturbations (0.97 ± 0.18 vs. 1.71 ± 0.29 m/s; p = 0.005). Center of pressure displacements were similar between groups. Our study demonstrated that engaging in Tai Chi could be beneficial to reactive postural responses after sudden perturbations in a horizontal direction; however, future interventional studies are needed to directly confirm this. Moreover, because of the age difference between the groups, some confounding effects of age cannot be ruled out.

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Assessing head acceleration to identify a motor threshold to galvanic vestibular stimulation

Journal of Neurophysiology ◽

10.1152/jn.00254.2020 ◽

2021 ◽

Author(s):

Youstina Mikhail ◽

Jonathan Charron ◽

Jean-Marc Mac Thiong ◽

Dorothy Barthélemy

Keyword(s):

Center Of Pressure ◽

Vestibular Function ◽

Vestibular Stimulation ◽

Galvanic Vestibular Stimulation ◽

Head Acceleration ◽

Motor Threshold ◽

Recruitment Curve ◽

Eyes Closed ◽

Postural Responses ◽

Significant Difference

Galvanic vestibular stimulation (GVS) is used to assess vestibular function, but vestibular responses can exhibit variability depending on protocols or intensities used. We measured head acceleration in healthy subjects to identify an objective motor threshold on which to base GVS intensity when assessing postural responses. Thirteen healthy right-handed subjects stood on a force platform, eyes closed, head facing forward. An accelerometer was placed on the vertex to detect head acceleration, and electromyography activity of the right soleus was recorded. GVS (200 ms; current steps 0.5;1-4mA) was applied in a binaural and bipolar configuration. 1) GVS induced a biphasic accelerometer response at a latency of 15 ms. Based on response amplitude, we constructed a recruitment curve for all participants and determined the motor threshold. In parallel, the method of limits was used to devise a more rapid approach to determine motor threshold. 2) We observed significant differences between motor threshold based on therecruitment curve and perceptual thresholds (sensation/perception of movement). No significant difference was observed between the motor threshold based on the method of limits and perceptual thresholds . 3) Using orthogonal polynomial contrasts, we observed a linear progression between multiples of the objective motor threshold (0.5, 0.75, 1, 1.5x motor threshold) and the 95% confidence ellipse area, the first peak of center of pressure velocity, and the short and medium latency responses in the soleus. Hence, an objective motor threshold and a recruitment curve for GVS were determined based on head acceleration, which could increase understanding of the vestibular system.

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