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Postural Control

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Definition

Postural control is defined as achievement, maintenance or regulation of balance during any static posture or dynamic activity for the regulation of stability and orientation [1]. The interaction of the individual with the task and the environment develops postural control [2]. Stability refers to maintenance of the centre of mass within the base of support while orientation refers to maintenance of relationship within the body segments and between body and the environment for the task [3]. These stability and orientation challenges necessitate change in the task and environment, thereby making postural control the most essential pre requisite for most of the tasks [4]. There are two types of postural control strategies: predictive and reactive, which utilize the feed forward and feedback postural control respectively in order to maintain stability during various circumstances [5]. Feed forward postural control refers to the postural adjustments made in response to the anticipation of a voluntary or a self-generated movement that may be destabilizing in while feedback postural control refer to the postural adjustments made in reaction to sensory stimuli from the externally generated perturbation [6]. Furthermore, these strategies may involve either a fixed-support or a change-in-support response depending on the intensity of the perturbation [7].

Systems involved in posture control

Postural control involves a complex interaction of multiple systems in order to maintain stability and orientation. Multi-components of the conceptual model of postural control include[8]: 1. Musculoskeletal components

2. Neuro muscular synergies 3. Individual sensory systems: visual, vestibular and somatosensory system 4. Sensory strategies 5. Anticipatory mechanisms 6. Adaptive mechanisms 7. Internal representations The functional task and the environment define the precise organization of the postural systems.

Background

Traditionally postural control was regarded an automatic response to sensory stimuli generated by subcortical structures such as the brainstem and spinal circuits[9]. Since postural responses are generated quickly, without voluntary intent and with less variability than cued, voluntary movements, cerebral cortex was not considered to be involved in postural control [10]. Hence cortical contribution to postural regulation is controversial and highly debatable [11]. Furthermore, it was assumed that since postural control is automatic in nature, it utilized only limited attentional resources [12]. However, current evolving evidence from numerous neurophysiological, behavioural and neuroimaging studies (as given below) suggest cortical involvement in postural control and maintenance of balance. Studies also indicate that postural control involved significant attentional resources and does require cognitive and sensory processes depending on other influencing factors [13].

Supportive evidence

Behavioral studies

Based on the central capacity theory, behavioral studies using dual-task paradigm are instrumental in evaluating the demands of attention for various postural tasks. According to the central capacity sharing theory, there are limited attentional resources and performance of any task demands utilization of some proportion of these resources[14]. In this model, there is simultaneous processing of multiple tasks and sharing of resources or processing capacity which results in slower processing of either of the tasks [15]. Dual task which involves performance of primary postural task (maintenance of a specific static or dynamic posture) and a secondary task (focal task involving use of the working memory) concurrently. This can lead to two possible outcomes: allocation of attentional resources to focal task during stance leading to impaired postural stability or allocation of attentional resources to maintain postural stability leading to poor performance on the focal task. Thus, such studies suggested the attentional demands of postural tasks[16].

Neurophysiological studies

An initial postural reaction on exposure to an external perturbations was shown to be generated by the brainstem and spinal cord in animal and human studies (short latency mono or polysynaptic spinal loop 40-65ms) [17] followed by the later part of the reaction which is modified by direct transcortical loops (long latency loops, ~132ms)[18]. Cerebral cortex via cerebellum which helps in adapting by using prior experience [19] or via basal ganglia which helps generating a response based on the current context, modifies the postural response [20].

Neuroimaging studies

Various functional neuroimaging techniques such as Functional near-infrared Spectroscopy, Functional magnetic resonance imaging, Positron emission tomography have been used to elucidate cortical control in static and dynamic postures. Using PET, Ouchi Y et al. 1999 [21] evaluated mechanisms involved in bipedal standing and confirmed the pivotal contribution of cerebellar vermis in maintenance of standing posture and further suggested involvement of the visual association cortex in controlling postural equilibrium while standing. Mauloin et al. 2003 [22] using PET studied motor imagery of locomotion under four conditions and confirmed supraspinal control in locomotion by demonstrating activation in the dorsal premotor cortex and precuneus bilaterally, the left dorsolateral prefrontal cortex, the left inferior parietal lobule, and the right posterior cingulate cortex. There was increased engagement of higher cortical structures noted with increase in demands of locomotor tasks. Using FMRI, Jahn et al 2004 [23] studied the activation pattern with three imagined conditions and found that standing was associated with activation of the thalamus, basal ganglia, and cerebellar vermis. Using fnirs, Mihara M et al. 2008 [24] studied activation related to external perturbation and suggested prefrontal cortex to be involved in adequate allocation of visuospatial attention. Zwergal A et al. 2012 [25] studied role of aging on activation pattern in standing and found more activation in bilateral insula, superior and middle temporal gyrus, inferior frontal gyrus, middle occipital gyrus and postcentral gyrus suggesting decreased reciprocal inhibition of these areas.

Factors affecting cortical control

The attentional demand to postural control is modulated by injury, pathology, aging, complexity of postural task and availability of sensory information.

References

  1. ^ Pollock AS1, Durward BR, Rowe PJ, Paul JP (2000). “What is balance?” Clinical rehabilitation 14(4):402-6; Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  2. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  3. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  4. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  5. ^ Pollock AS1, Durward BR, Rowe PJ, Paul JP (2000). “What is balance?” Clinical rehabilitation 14(4):402-6; Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  6. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  7. ^ Pollock AS1, Durward BR, Rowe PJ, Paul JP (2000). “What is balance?” Clinical rehabilitation 14(4):402-6
  8. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  9. ^ Sherrington, C. S. (1910). Flexion‐reflex of the limb, crossed extension‐reflex, and reflex stepping and standing. The Journal of physiology, 40(1-2), 28-121; Magnus, R. (1926). The physiology of posture: Cameron Lectures. Lancet, 211(53), 1-536
  10. ^ Diener, H. C., Dichgans, J., Bootz, F., & Bacher, M. (1984). Early stabilization of human posture after a sudden disturbance: influence of rate and amplitude of displacement. Experimental Brain Research, 56(1), 126-134; Keck, M. E., Pijnappels, M., Schubert, M., Colombo, G., Curt, A., & Dietz, V. (1998). Stumbling reactions in man: influence of corticospinal input. Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control, 109(3), 215-223
  11. ^ Jacobs, J. V., & Horak, F. B. (2007). Cortical control of postural responses. Journal of neural transmission, 114(10), 1339-1348
  12. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  13. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  14. ^ Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  15. ^ Tombu, M., & Jolicœur, P. (2003). A central capacity sharing model of dual-task performance. Journal of Experimental Psychology: Human Perception and Performance, 29(1),3
  16. ^ Tombu, M., & Jolicœur, P. (2003). A central capacity sharing model of dual-task performance. Journal of Experimental Psychology: Human Perception and Performance, 29(1),3
  17. ^ Bove, M., Nardone, A., & Schieppati, M. (2003). Effects of leg muscle tendon vibration on group Ia and group II reflex responses to stance perturbation in humans. J Physiol, 550(Pt 2), 617-630. doi:10.1113/jphysiol.2003.043331
  18. ^ Ackermann, H., Diener, H. C., & Dichgans, J. (1987). Changes in sensorimotor functions after spinal lesions evaluated in terms of long-latency reflexes. J Neurol Neurosurg Psychiatry, 50(12), 1647-1654; Jacobs, J. V., & Horak, F. B. (2007). Cortical control of postural responses. Journal of neural transmission, 114(10), 1339-1348
  19. ^ Graydon, F. X., Friston, K. J., Thomas, C. G., Brooks, V. B., & Menon, R. S. (2005). Learning-related fMRI activation associated with a rotational visuo-motor transformation. Brain Res Cogn Brain Res, 22(3), 373-383. doi:10.1016/j.cogbrainres.2004.09.007
  20. ^ Jacobs, J. V., & Horak, F. B. (2007). Cortical control of postural responses. Journal of neural transmission, 114(10), 1339-1348
  21. ^ Ouchi, Y., Okada, H., Yoshikawa, E., Nobezawa, S., & Futatsubashi, M. (1999). Brain activation during maintenance of standing postures in humans. Brain, 122(2), 329-338
  22. ^ Malouin, F., Richards, C. L., Jackson, P. L., Dumas, F., & Doyon, J. (2003). Brain activations during motor imagery of locomotor‐related tasks: A PET study. Human brain mapping, 19(1), 47-62
  23. ^ Jahn, K., Deutschländer, A., Stephan, T., Strupp, M., Wiesmann, M., & Brandt, T. (2004). Brain activation patterns during imagined stance and locomotion in functional magnetic resonance imaging. Neuroimage, 22(4), 1722-1731
  24. ^ Mihara, M., Miyai, I., Hatakenaka, M., Kubota, K., & Sakoda, S. (2008). Role of the prefrontal cortex in human balance control. Neuroimage, 43(2), 329-336
  25. ^ Zwergal, A., Linn, J., Xiong, G., Brandt, T., Strupp, M., & Jahn, K. (2012). Aging of human supraspinal locomotor and postural control in fMRI. Neurobiology of aging, 33(6), 1073-1084
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