Motor Imagery during Action Observation: A Brief Review of Evidence, Theory and Future Research Opportunities

Daniel L Eaves, Martin Riach, Paul S Holmes, David J Wright, Daniel L Eaves, Martin Riach, Paul S Holmes, David J Wright

Abstract

Motor imagery (MI) and action observation (AO) have traditionally been viewed as two separate techniques, which can both be used alongside physical practice to enhance motor learning and rehabilitation. Their independent use has largely been shown to be effective, and there is clear evidence that the two processes can elicit similar activity in the motor system. Building on these well-established findings, research has now turned to investigate the effects of their combined use. In this article, we first review the available neurophysiological and behavioral evidence for the effects of combined action observation and motor imagery (AO+MI) on motor processes. We next describe a conceptual framework for their combined use, and then discuss several areas for future research into AO+MI processes. In this review, we advocate a more integrated approach to AO+MI techniques than has previously been adopted by movement scientists and practitioners alike. We hope that this early review of an emergent body of research, along with a related set of research questions, can inspire new work in this area. We are optimistic that future research will further confirm if, how, and when this combined approach to AO+MI can be more effective in motor learning and rehabilitation settings, relative to the more traditional application of MI or AO independently.

Keywords: AO+MI; combined action observation and motor imagery; mental practice; motor learning; motor rehabilitation; motor simulation; movement demonstrations; observational learning.

References

    1. Bek J., Poliakoff E., Marshall H., Trueman S., Gowen E. (2016). Enhancing voluntary imitation through attention and motor imagery. Exp. Brain Res. 234, 1819–1828. 10.1007/s00221-016-4570-3
    1. Berends H. I., Wolkorte R., Ijzerman M. J., van Putten M. J. A. M. (2013). Differential cortical activation during observation and observation-and-imagination. Exp. Brain Res. 229, 337–345. 10.1007/s00221-013-3571-8
    1. Braun S., Kleynen M., van Heel T., Kruithof N., Wade D., Beurskens A. (2013). The effects of mental practice in neurological rehabilitation; a systematic review and meta-analysis. Front. Hum. Neurosci. 7:390. 10.3389/fnhum.2013.00390
    1. Braun S. M., Beurskens A., Kleynen M., Oudelaar B., Schols J. M., Wade D. T. (2012). A multicentre randomized controlled trial to compare subacute ‘treatment as usual’ with and without mental practice among persons with stroke in Dutch nursing homes. J. Am. Med. Dir. Assoc. 13, 85.e1–e7. 10.1016/j.jamda.2010.07.009
    1. Buccino G. (2014). Action observation treatment: a novel tool in neurorehabilitation. Phil. Trans. R. Soc. B 369:20130185. 10.1098/rstb.2013.0185
    1. Buccino G., Lui F., Canessa N., Patteri I., Lagravinese G., Benuzzi F., et al. . (2004). Neural circuits involved in the recognition of actions performed by nonconspecifics: an fMRI study. J. Cogn. Neurosci. 16, 114–126. 10.1162/089892904322755601
    1. Burgess P. W., Dumontheil I., Gilbert S. J. (2007). The gateway hypothesis of rostral prefrontal cortex (area 10). Function. Trends Cogn. Sci. 11, 290–298. 10.1016/j.tics.2007.05.004
    1. Burgess P. W., Simons J. S., Dumontheil I., Gilbert S. J. (2005). The gateway hypothesis of rostral prefrontal cortex (area 10). Function, in Measuring the Mind: Speed Control and Age, eds Duncan J., Philips L., McLeod P. (London, England: Oxford University Press; ), 215–246.
    1. Callow N., Hardy L. (2004). The relationship between the use of kinaesthetic imagery and different visual imagery perspectives. J. Sport Sci. 22, 167–177. 10.1080/02640410310001641449
    1. Caramazza A., Anzellotti S., Strnad L., Lingnau A. (2014). Embodied cognition and mirror neurons: a critical assessment. Annu. Rev. Neurosci. 37, 1–15. 10.1146/annurev-neuro-071013-013950
    1. Caspers S., Zilles K., Laird A. R., Eickhoff S. B. (2010). ALE meta-analysis of action observation and imitation in the human brain. Neuroimage 50, 1148–1167. 10.1016/j.neuroimage.2009.12.112
    1. Chen X., Bin G., Daly I., Gao X. (2013). Event-related desynchronization (ERD). in the alpha band during a hand mental rotation task. Neurosci. Lett. 541, 238–242. 10.1016/j.neulet.2013.02.036
    1. Cisek P., Kalaska J. F. (2010). Neural mechanisms for interacting with a world full of action choices. Annu. Rev. Neurosci. 33, 269–298. 10.1146/annurev.neuro.051508.135409
    1. Clark S., Tremblay F., Ste-Marie D. (2004). Differential modulation of corticospinal excitability during observation, mental imagery and imitation of hand actions. Neuropsychologia 42, 105–112. 10.1016/S0028-3932(03)00144-1
    1. Cumming J., Cooley S. J., Anuar N., Kosteli M. C., Quinton M. L., Weibull F., et al. (2016). Developing imagery ability effectively: a guide to layered stimulus response training. J. Sport Psychol. Action. 1–11. 10.1080/21520704.2016.1205698
    1. de Vries S., Mulder T. (2007). Motor imagery and stroke rehabilitation: a critical discussion. J. Rehab. Med. 39, 5–13. 10.2340/16501977-0020
    1. Diersch N., Jones A. L., Cross E. S. (2016). The timing and precision of action prediction in the aging brain. Hum. Brain Mapp. 37, 54–66. 10.1002/hbm.23012
    1. Dijkerman H. C., Ietswaart M., Johnston M., MacWalter R. S. (2004). Does motor imagery training improve hand function in chronic stroke patients? A pilot study. Clin. Rehabil. 18, 583–549. 10.1191/0269215504cr769oa
    1. Di Rienzo F., Blache Y., Kanthack T. F. D., Monteil K., Collet C., Guillot A. (2015). Short-term effects of integrated motor imagery practice on muscle activation and force performance. Neuroscience 305, 146–156. 10.1016/j.neuroscience.2015.07.080
    1. Di Rienzo F., Debarnot U., Daligault S., Saruco E., Delpuech C., Doyon J., et al. . (2016). Online and offline performance gains following motor imagery practice: a comprehensive review of behavioral and neuroimaging studies. Front. Hum. Neurosci. 10:315. 10.3389/fnhum.2016.00315
    1. Eaves D. L., Behmer L., Jr., Vogt S. (2016). EEG and behavioural correlates of different forms of motor imagery during action observation. Brain Cogn. 106, 90–103. 10.1016/j.bandc.2016.04.013
    1. Eaves D. L., Haythornthwaite L., Vogt S. (2014). Motor imagery during action observation modulates automatic imitation effects in rhythmical actions. Front. Hum. Neurosci. 8:28. 10.3389/fnhum.2014.00028
    1. Eaves D. L., Turgeon M., Vogt S. (2012). Automatic imitation in rhythmical actions: kinematic fidelity and the effects of compatibility, delay, and visual monitoring. PLoS ONE 7:e46728. 10.1371/journal.pone.0046728
    1. Ertelt D., Small S., Solodkin A., Dettmers C., McNamara A., Binkofski F., et al. . (2007). Action observation has a positive impact on rehabilitation of motor deficits after stroke. Neuroimage 36, T164–T173. 10.1016/j.neuroimage.2007.03.043
    1. Ewan L. M., Smith N. C., Holmes P. S. (2010). Disruption to aspects of imagery vividness following stroke. J. Ment. Imagery. 34, 3–14.
    1. Filimon F., Nelson J. D., Hagler D. J., Sereno M. I. (2007). Human cortical representations for reaching: mirror neurons for execution, observation, and imagery. Neuroimage 37, 1315–1328. 10.1016/j.neuroimage.2007.06.008
    1. Filimon F., Rieth C. A., Sereno M. I., Cottrell G. W. (2015). Observed, executed, and imagined action representations can be decoded from ventral and dorsal areas. Cereb. Cortex 25, 3144–3158. 10.1093/cercor/bhu110
    1. Franceschini M., Ceravolo M. G., Agosti M., Cavallini P., Bonassi S., Dall'Armi V., et al. . (2012). Clinical relevance of action observation in upper-limb stroke rehabilitation: a possible role in recovery of functional dexterity. A randomized clinical trial. Neurorehabil. Neural Repair. 26, 456–462. 10.1177/1545968311427406
    1. Ganis G., Keenan J. P., Kosslyn S. M., Pascual-Leone A. (2000). Transcranial magnetic stimulation of primary motor cortex affects mental rotation. Cereb. Cortex. 10, 175–180. 10.1093/cercor/10.2.175
    1. Gatti R., Tettamanti A., Gough P. M., Riboldi E., Marinoni L., Buccino G. (2013). Action observation versus motor imagery in learning a complex motor task: a short review of literature and a kinematics study. Neurosci. Lett. 540, 37–42. 10.1016/j.neulet.2012.11.039
    1. Gonzalez-Rosa J. J., Natali F., Tettamanti A., Cursi M., Velikova S., Comi G., et al. . (2015). Action observation and motor imagery in performance of complex movements: evidence from EEG and kinematics analysis. Behav. Brain Res. 281, 290–300. 10.1016/j.bbr.2014.12.016
    1. Grèzes J., Decety J. (2001). Functional anatomy of execution, mental simulation, observation, and verb generation of actions: a meta-analysis. Hum. Brain Mapp. 12, 1–19. 10.1002/1097-0193(200101)12:1<1::aid-hbm10>;2-v
    1. Grosprêtre S., Ruffino C., Lebon F. (2016). Motor imagery and cortico-spinal excitability: a review. Eur. J. Sport Sci. 16, 317–324. 10.1080/17461391.2015.1024756
    1. Helm F., Marinovic W., Krüger B., Munzert J., Riek S. (2015). Corticospinal excitability during imagined and observed dynamic force production tasks: effortfulness matters. Neuroscience 290, 398–405. 10.1016/j.neuroscience.2015.01.050
    1. Hétu S., Grégoire M., Saimpont A., Coll M. P., Eugene F., Michon P. E., et al. . (2013). The neural network of motor imagery: an ALE meta-analysis. Neurosci. Biobehav. Rev. 37, 930–949. 10.1016/j.neubiorev.2013.03.017
    1. Hickok G. (2014). The Myth of Mirror Neurons: The Real Neuroscience of Communication and Cognition. New York, NY: WW Norton & Company.
    1. Higuchi S., Holle H., Roberts N., Eickhoff S. B., Vogt S. (2012). Imitation and observational learning of hand actions: prefrontal involvement and connectivity. Neuroimage 59, 1668–1683. 10.1016/j.neuroimage.2011.09.021
    1. Hodges N. J., Williams A. M., Hayes S. J., Breslin G. (2007). What is modelled during observational learning? J. Sports Sci. 25, 531–545. 10.1080/02640410600946860
    1. Holmes P., Calmels C. (2008). A neuroscientific review of imagery and observation use in sport. J. Mot. Behav. 40, 433–445. 10.3200/JMBR.40.5.433-445
    1. Holmes P. S. (2007). Theoretical and practical problems for imagery in stroke rehabilitation: an observation solution. Rehab. Psychol. 52, 1–10. 10.1037/0090-5550.52.1.1
    1. Hoyek N., Di Rienzo F., Collet C., Hoyek F., Guillot A. (2014). The therapeutic role of motor imagery on the functional rehabilitation of a stage II shoulder impingement syndrome. Disabil. Rehabil. 36, 1113–1119. 10.3109/09638288.2013.833309
    1. Ietswaart M., Johnston M., Dijkerman H. C., Joice S., Scott C. L., MacWalter R. S., et al. . (2011). Mental practice with motor imagery in stroke recovery: randomized controlled trial of efficacy. Brain 134, 1373–1386. 10.1093/brain/awr077
    1. Ingram T. G., Kraeutner S. N., Solomon J. P., Westwood D. A., Boe S. G. (2016). Skill acquisition via motor imagery relies on both motor and perceptual learning. Behav. Neurosci. 130, 252. 10.1037/bne0000126
    1. Jeannerod M. (2001). Neural simulation of action: a unifying mechanism for motor cognition. Neuroimage 14, S103–S109. 10.1006/nimg.2001.0832
    1. Jeannerod M. (2006). Motor Cognition. Oxford: Oxford University Press.
    1. Kalicinski M., Kempe M., Bock O. (2015). Motor imagery: effects of age, task complexity, and task setting. Exp. Aging Res. 41, 25–38. 10.1080/0361073X.2015.978202
    1. Lang P. (1977). Imagery in therapy: an information processing analysis of fear. Behav. Ther. 8, 862–886. 10.1016/S0005-7894(77)80157-3
    1. Lang P. (1979). A bio-informational theory of emotional imagery. Psychophysiology 16, 495–512. 10.1111/j.1469-8986.1979.tb01511.x
    1. Lorey B., Naumann T., Pilgramm S., Petermann C., Bischoff M., Zentgraf K., et al. . (2013). How equivalent are the action execution, imagery, and observation of intransitive movements. Revisiting the concept of somatotopy during action simulation. Brain Cogn. 81, 139–150. 10.1016/j.bandc.2012.09.011
    1. Machado S., Lattari E., de Sa A. S., Rocha N. B. F., Yuan T.-F., Paes F., et al. . (2015). Is mental practice an effective adjunct therapeutic strategy for upper limb motor restoration after stroke? A systematic review and meta-analysis. CNS Neuro. Disord. Drug Targets 14, 567–575. 10.2174/1871527314666150429112702
    1. Macuga K. L., Frey S. H. (2012). Neural representations involved in observed, imagined, and imitated actions are dissociable and hierarchically organized. Neuroimage 59, 2798–2807. 10.1016/j.neuroimage.2011.09.083
    1. Mateo S., Di Rienzo F., Bergeron V., Guillot A., Collet C. (2015). Motor imagery reinforces brain compensation of reach-to-grasp movement after cervical spinal cord injury. Front. Behav. Neurosci. 9:234. 10.3389/fnbeh.2015.00234
    1. Molina M., Tijus C., Jouen F. (2008). The emergence of motor imagery in children. J. Exp. Child Psychol. 99, 196–209. 10.1016/j.jecp.2007.10.001
    1. Mouthon A., Ruffieux J., Wälchli M., Keller M., Taube W. (2015). Task-dependent changes of corticospinal excitability during observation and motor imagery of balance tasks. Neuroscience 303, 535–543. 10.1016/j.neuroscience.2015.07.031
    1. Munzert J., Zentgraf K., Stark R., Vaitl D. (2008). Neural activation in cognitive motor processes: comparing motor imagery and observation of gymnastic movements. Exp. Brain Res. 188, 437–444. 10.1007/s00221-008-1376-y
    1. Naish K. R., Houston-Price C., Bremner A. J., Holmes N. P. (2014). Effects of action observation on corticospinal excitability: muscle specificity, direction and timing of the mirror response. Neuropsychologia 64, 331–348. 10.1016/j.neuropsychologia.2014.09.034
    1. Nedelko V., Hassa T., Hamzei F., Schoenfeld M. A., Dettmers C. (2012). Action imagery combined with action observation activates more corticomotor regions than action observation alone. J. Neurol. Phys. Ther. 36, 182–188. 10.1097/NPT.0b013e318272cad1
    1. Neuper C., Scherer R., Wriessnegger S., Pfurtscheller G. (2009). Motor imagery and action observation: modulation of sensorimotor brain rhythms during mental control of a brain-computer interface. Clin. Neurophysiol. 120, 239–247. 10.1016/j.clinph.2008.11.015
    1. Ohno K., Higashi T., Sugawara K., Ogahara K., Funase K., Kasai T. (2011). Excitability changes in the human primary motor cortex during observation with motor imagery of chopstick use. J. Phys. Ther. Sci. 23, 703–706. 10.1589/jpts.23.703
    1. Page S. J., Levine P., Leonard A. (2005). Effects of mental practice on affected limb use and function in chronic stroke. Arch. Phys. Med. Rehabil. 86, 399–402. 10.1016/j.apmr.2004.10.002
    1. Page S. J., Levine P., Leonard A. (2007). Mental practice in chronic stroke: results of a randomised, placebo-controlled trial. Stroke 38, 1293–1297. 10.1161/01.STR.0000260205.67348.2b
    1. Pilgramm S., de Haas B., Helm F., Zentgraf K., Stark R., Munzert J., et al. . (2016). Motor imagery of hand actions: decoding the content of motor imagery from brain activity in frontal and parietal motor areas. Hum. Brain Mapp. 37, 81–93. 10.1002/hbm.23015
    1. Porro C. A., Facchin P., Fusi S., Dri G., Fadiga L. (2007). Enhancement of force after action observation: behavioural and neurophysiological studies. Neuropsychologia 45, 3114–3121. 10.1016/j.neuropsychologia.2007.06.016
    1. Rizzolatti G., Sinigaglia C. (2010). The functional role of the parieto-frontal mirror circuit: interpretations and misinterpretations. Nat. Rev. Neurosci. 11, 264–274. 10.1038/nrn2805
    1. Rozand V., Lebon F., Papaxanthis C., Lepers R. (2014). Does a mental training session induce neuromuscular fatigue? Med. Sci. Sports Exerc. 46, 1981–1989. 10.1249/MSS.0000000000000327
    1. Rymal A. M., Ste-Marie D. M. (2009). Does self-modeling affect imagery ability or vividness? J. Imagery. Res. Sport Phys. Activity 4, 1–14. 10.2202/1932-0191.1035
    1. Sakamoto M., Muraoka T., Mizuguchi N., Kanosue K. (2009). Combining observation and imagery of an action enhances human corticospinal excitability. Neurosci. Res. 65, 23–27. 10.1016/j.neures.2009.05.003
    1. Sale P., Franceschini M. (2012). Action observation and mirror neuron network: a tool for motor stroke rehabilitation. Eur. J. Phys. Rehab. Med. 48, 313–318.
    1. Sarasso E., Gemma M., Agosta F., Filippi M., Gatti R. (2015). Action observation training to improve motor function recovery: a systematic review. Arch. Physiother. 5, 1 10.1186/s40945-015-0013-x
    1. Schuster C., Hilfiker R., Amft O., Scheidhauer A., Andrews B., Butler J., et al. . (2011). Best practice for motor imagery: a systematic literature review on motor imagery training elements in five different disciplines. BMC Med. 9:75. 10.1186/1741-7015-9-75
    1. Sharma N., Pomeroy V. M., Baron J. C. (2006). Motor imagery: a backdoor to the motor system after stroke? Stroke 37, 1941–1952. 10.1161/01.str.0000226902.43357.fc
    1. Shepard R. N. (1984). Ecological constraints on internal representation: resonant kinematics of perceiving, imagining, thinking, and dreaming. Psychol. Rev. 91, 417–447. 10.1037/0033-295x.91.4.417
    1. Smith D., Holmes P. (2004). The effect of imagery modality of golf putting performance. J. Sport Exerc. Psychol. 26, 385–395. 10.1123/jsep.26.3.385
    1. Springer A., Parkinson J., Prinz W. (2013). Action simulation: time course and representational mechanisms. Front. Psychol. 4:387. 10.3389/fpsyg.2013.00387
    1. Spruijt S., van der Kamp J., Steenbergen B. (2015). Current insights in the development of children's motor imagery ability. Front. Psychol. 6:787. 10.3389/fpsyg.2015.00787
    1. Ste-Marie D. M., Law B., Rymal A. M., Jenny O., Hall C., McCullagh P. (2012). Observation interventions for motor skill learning and performance: an applied model for the use of observation. Int. Rev. Sport Exerc. Psychol. 5, 145–176. 10.1080/1750984X.2012.665076
    1. Stinear C. M., Byblow W. D., Steyvers M., Levin O., Swinnen S. P. (2006). Kinesthetic, but not visual, motor imagery modulates corticomotor excitability. Exp. Brain Res. 168, 157–164. 10.1007/s00221-005-0078-y
    1. Sun Y., Wei W., Luo Z., Gan H., Hu X. (2016). Improving motor imagery practice with synchronous action observation in stroke patients. Top. Stroke Rehabil. 23, 245–253. 10.1080/10749357.2016.1141472
    1. Szameitat A. J., Shen S., Conforto A., Sterr A. (2012). Cortical activation during executed, imagined, observed, and passive wrist movements in healthy volunteers and stroke patients. Neuroimage 62, 266–280. 10.1016/j.neuroimage.2012.05.009
    1. Taube W., Lorch M., Zeiter S., Keller M. (2014). Non-physical practice improves task performance in an unstable, perturbed environment: motor imagery and observational balance training. Front. Hum. Neurosci. 8:972. 10.3389/fnhum.2014.00972
    1. Taube W., Mouthon M., Leukel C., Hoogewood H. M., Annoni J. M., Keller M. (2015). Brain activity during observation and motor imagery of different balance tasks: An fMRI study. Cortex 64, 102–114. 10.1016/j.cortex.2014.09.022
    1. Tsukazaki I., Uehara K., Morishita T., Ninomiya M., Funase K. (2012). Effect of observation combined with motor imagery of a skilled hand-motor task on motor cortical excitability: difference between novice and expert. Neurosci. Lett. 518, 96–100. 10.1016/j.neulet.2012.04.061
    1. Vannuscorps G., Caramazza A. (2016). Typical action perception and interpretation without motor simulation. Proc. Natl. Acad. Sci. U.S.A. 113, 86–91. 10.1073/pnas.1516978112
    1. Villiger M., Estévez N., Hepp-Reymond M.-C., Kiper D., Kollias S. S., Eng K., et al. . (2013). Enhanced activation of motor execution networks using action observation combined with imagination of lower limb movements. PLoS ONE 8:e72403. 10.1371/journal.pone.0072403
    1. Vogt S., Buccino G., Wohlschläger A. M., Canessa N., Shah N., Zilles K., et al. . (2007). Prefrontal involvement in imitation learning of hand actions: effects of practice and expertise. Neuroimage 37, 1371–1383. 10.1016/j.neuroimage.2007.07.005
    1. Vogt S., Di Rienzo F., Collet C., Collins A., Guillot A. (2013). Multiple roles of motor imagery during action observation. Front. Hum. Neurosci. 7:807. 10.3389/fnhum.2013.00807
    1. Williams J., Pearce A. J., Loporto M., Morris T., Holmes P. S. (2012). The relationship between corticospinal excitability during motor imagery and motor imagery ability. Behav. Brain Res. 226, 369–375. 10.1016/j.bbr.2011.09.014
    1. Williams S. E., Cooley S. J., Cumming J. (2013). Layered stimulus response training improves motor imagery ability and movement execution. J. Sport Exerc. Psychol. 35, 60–71. 10.1123/jsep.35.1.60
    1. Wilson P., Green D., Caeyenberghs K., Steenbergen B., Duckworth J. (2016). Integrating new technologies into the treatment of CP and DCD. Curr. Dev. Disord. Rep. 3, 138–151. 10.1007/s40474-016-0083-9
    1. Wilson P. H., Maruff P., Ives S., Currie J. (2001). Abnormalities of motor and praxis imagery in children with DCD. Hum. Mov. Sci. 20, 135–159. 10.1016/S0167-9457(01)00032-X
    1. Wilson P. H., Thomas P. R., Maruff P. (2002). Motor imagery training ameliorates motor clumsiness in children. J. Child Neurol. 17, 491–498. 10.1177/088307380201700704
    1. Wright C. J., Smith D. (2009). The effect of PETTLEP imagery on strength performance. Int. J. Sport Exerc. Psychol. 7, 18–31. 10.1080/1612197X.2009.9671890
    1. Wright D. J., McCormick S. A., Birks S., Loporto M., Holmes P. S. (2015). Action observation and imagery training improve the ease with which athletes can generate imagery. J. Appl. Sport Psychol. 27, 156–170. 10.1080/10413200.2014.968294
    1. Wright D. J., McCormick S. A., Williams J., Holmes P. S. (2016). Viewing instructions accompanying action observation modulate corticospinal excitability. Front. Hum. Neurosci. 10:17. 10.3389/fnhum.2016.00017
    1. Wright D. J., Williams J., Holmes P. S. (2014). Combined action observation and imagery facilitates corticospinal excitability. Front. Hum. Neurosci. 8:951. 10.3389/fnhum.2014.00951
    1. Zabicki A., de Haas B., Zentgraf K., Stark R., Munzert J., Krüger B. (2016). Imagined and executed actions in the human motor system: testing neural similarity between execution and imagery of actions with a multivariate approach. Cereb. Cortex. 10.1093/cercor/bhw257
    1. Zacks J. M. (2008). Neuroimaging studies of mental rotation: a meta-analysis and review. J. Cogn. Neurosci. 20, 1–19. 10.1162/jocn.2008.20013
    1. Zimmermann-Schlatter A., Schuster C., Puhan M. A., Siekierka E., Steurer J. (2008). Efficacy of motor imagery in post-stroke rehabilitation: a systematic review. J. Neuroeng. Rehabil. 5:8. 10.1186/1743-0003-5-8.

Source: PubMed

3
Abonner