Unsolved:Postural Control

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Short description: Maintenance of body posture in space


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 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

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 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.[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]

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

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.

Cortical control of posture

Traditionally postural control was regarded an automatic response to sensory stimuli generated by subcortical structures such as the brainstem and spinal circuits.[7] 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.[8] 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

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) [9] followed by the later part of the reaction which is modified by direct transcortical loops (long latency loops, ~132 ms).[10] Cerebral cortex via cerebellum which helps in adapting by using prior experience [11] or via basal ganglia which helps generating a response based on the current context, modifies the postural response.[12]

Neuroimaging studies

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 [13] 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 [14] 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 [15] 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 [16] studied activation related to external perturbation and suggested prefrontal cortex to be involved in adequate allocation of visuospatial attention. Zwergal A et al. 2012 [17] 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

  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. http://dx.doi.org/10.1152/jn.2002.88.3.1097. 
  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" (in en). The American Journal of Sports Medicine 25 (1): 130–137. doi:10.1177/036354659702500126. ISSN 0363-5465. http://journals.sagepub.com/doi/10.1177/036354659702500126. 
  4. 4.0 4.1 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
  5. 5.0 5.1 5.2 5.3 5.4 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. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. Jacobs, J. V., & Horak, F. B. (2007). Cortical control of postural responses. Journal of neural transmission, 114(10), 1339-1348
  13. 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
  14. 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
  15. 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
  16. 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
  17. 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