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Postural Control

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Postural control refers to the maintenance of body posture in space. The central nervous system interprets sensory input to produce motor output that maintains upright posture.[1] Sensory information used for postural control largely comes from visual, proprioceptive, and vestibular systems.[2] While the ability to regulate posture in vertebrates was previously thought to be a mostly automatic task, controlled by circuits in the spinal cord and brainstem, it is now clear that cortical areas are also involved, updating motor commands based on the state of the body and environment.[3]

Definition

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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.[4] The interaction of the individual with the task and the environment develops postural control.[5] Stability refers to maintenance of the center 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.[5] These stability and orientation challenges necessitate change in the task and environment, thereby making postural control the most essential prerequisite for most of the tasks.[5]

Postural control strategies

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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.[4] 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, while feedback postural control refer to the postural adjustments made in reaction to sensory stimuli from the externally generated perturbation.[5] Furthermore, these strategies may involve either a fixed-support or a change-in-support response depending on the intensity of the perturbation.[6]

Systems involved in posture control

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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:[5]

  • Musculoskeletal components
  • Neuro muscular synergies
  • Individual sensory systems: visual, vestibular and somatosensory system
  • Sensory strategies
  • Anticipatory mechanisms
  • Adaptive mechanisms
  • Internal representations

The functional task and the environment define the precise organization of the postural systems.

Postural control reflexes

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Many animals have reflexes that aid in postural control. One of the most widespread feedback systems in limb postural control is the resistance reflex in arthropods and stretch reflex in vertebrates.[7][8] These feedback loops consist of sensory neurons that detect external perturbations and activate motor neurons that produce movements that counter the imposed movement.[9]

In some cases, a resistance reflex is reversed in certain contexts, becoming an ‘assistance reflex’ - causing movement in the same direction as the perturbation. For example, in the crayfish, perturbation of the leg causes a resistance reflex when the animal is standing, but an assistance reflex when the animal is walking. [10] This phenomenon is called ‘reflex reversal’, where the reflex response to a stimulus changes given the state of the animal.[11]

Cortical control of posture

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Traditionally postural control was regarded an automatic response to sensory stimuli generated by subcortical structures such as the brainstem and spinal circuits.[12] 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.[13] However, current evolving evidence from numerous neurophysiological and neuroimaging studies (as given below) suggest cortical involvement in postural control and maintenance of balance.

Neurophysiological studies

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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) [14] followed by the later part of the reaction which is modified by direct transcortical loops (long latency loops, ~132 ms).[15] Cerebral cortex via cerebellum which helps in adapting by using prior experience [16] or via basal ganglia which helps generating a response based on the current context, modifies the postural response.[17]

Neuroimaging studies

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Various functional neuroimaging techniques such as Functional near-infrared spectroscopy, Functional magnetic resonance imaging, and Positron emission tomography have been used to elucidate cortical control in static and dynamic postures. Using PET, Ouchi Y et al. 1999 [18] 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 [19] 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 [20] 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 [21] studied activation related to external perturbation and suggested prefrontal cortex to be involved in adequate allocation of visuospatial attention. Zwergal A et al. 2012 [22] 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.

References

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  1. ^ Massion, J. (1994). Postural control system. Current Opinion in Neurobiology, 4(6), 877-887
  2. ^ Peterka, R. J. (2002-09-01). "Sensorimotor Integration in Human Postural Control". Journal of Neurophysiology. 88 (3): 1097–1118. doi:10.1152/jn.2002.88.3.1097. ISSN 0022-3077. PMID 12205132. S2CID 14674302.
  3. ^ Lephart, Scott M.; Pincivero, Danny M.; Giraido, Jorge L.; Fu, Freddie H. (January 1997). "The Role of Proprioception in the Management and Rehabilitation of Athletic Injuries". The American Journal of Sports Medicine. 25 (1): 130–137. doi:10.1177/036354659702500126. ISSN 0363-5465. PMID 9006708. S2CID 8912431.
  4. ^ a b 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
  5. ^ a b c d e Anne Shumway Cook, Wollcott (2007) Motor control, 3rd edition
  6. ^ Pollock AS1, Durward BR, Rowe PJ, Paul JP (2000). “What is balance?” Clinical rehabilitation 14(4):402-6
  7. ^ Capaday, Charles (November 2000). "Control of a 'simple' stretch reflex in humans". Trends in Neurosciences. 23 (11): 528–529. doi:10.1016/s0166-2236(00)01664-7. ISSN 0166-2236. PMID 11185390. S2CID 19227924.
  8. ^ Clarac, François; Cattaert, Daniel; Le Ray, Didier (May 2000). "Central control components of a 'simple' stretch reflex". Trends in Neurosciences. 23 (5): 199–208. doi:10.1016/s0166-2236(99)01535-0. ISSN 0166-2236. PMID 10782125. S2CID 10113723.
  9. ^ Le Bon-Jego, Morgane; Cattaert, Daniel (2002-11-01). "Inhibitory Component of the Resistance Reflex in the Locomotor Network of the Crayfish". Journal of Neurophysiology. 88 (5): 2575–2588. doi:10.1152/jn.00178.2002. ISSN 0022-3077. PMID 12424295.
  10. ^ Le Ray, D.; Cattaert, D. (April 1997). "Neural mechanisms of reflex reversal in coxo-basipodite depressor motor neurons of the crayfish". Journal of Neurophysiology. 77 (4): 1963–1978. doi:10.1152/jn.1997.77.4.1963. ISSN 0022-3077. PMID 9114248. S2CID 15322398.
  11. ^ "reflex-reversal phenomenon". The Oxford Dictionary of Sports Science & Medicine. Oxford University Press. 2007. doi:10.1093/acref/9780198568506.001.0001. ISBN 9780191727788.
  12. ^ 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
  13. ^ 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
  14. ^ 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
  15. ^ 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
  16. ^ 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
  17. ^ Jacobs, J. V., & Horak, F. B. (2007). Cortical control of postural responses. Journal of neural transmission, 114(10), 1339-1348
  18. ^ 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
  19. ^ 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
  20. ^ 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
  21. ^ 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
  22. ^ 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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