Action observation has a positive impact on rehabilitation of motor deficits after stroke
Introduction
Motor deficiency is the leading cause of disability following stroke (Duncan et al., 1992). The mechanisms underlying recovery are multifold including active relearning strategies and passive processes of lesion adaptation (Seitz et al., 2002). The traditional neurorehabilitative approach to treat motor deficits after stroke is mainly based on techniques aiming at stimulating the use of the paretic limb during supervised training sessions (Rossetti et al., 2005). The main tenet is that practice of repetitive, active movements by a paretic limb leads to effects induced by positive neuronal plasticity. The effects of repetitive training are empirically well proven (Shepherd, 2001, Aichner et al., 2002, Jang et al., 2003, Byl et al., 2003, Dombovy, 2004): this approach was demonstrated to be more effective than conventional physiotherapeutic approaches (Beer, 2000, Hesse et al., 2002), with a smaller learning time of manual arm movements (Beer, 2000), a faster recovery and smaller therapy lasts (Kwakkel et al., 1999). Examples include the “constraint-induced movement therapy” (Taub et al., 1993, Duncan, 1997, Elbert et al., 2003), the motor relearning program (Langhammer and Stanghelle, 2003), and repetitive arm training (Buetefisch et al., 1995). These neurorehabilitative trainings are supposed to have attained the best rehabilitative outcomes so far.
There is increasing experimental evidence that motor areas are recruited not only when actions are actually executed, but also when they are mentally rehearsed or simply observed (for a review see Jeannerod, 2001). The neurophysiological basis for this recruitment relies on the discovery of mirror neurons, first described in the monkey (Rizzolatti et al., 1996, Gallese et al., 1996). These neurons discharge when the animal performs an object-related action with the hand or the mouth and when it observes the same or a similar action done by another individual. It has been shown, also in humans, that the observation of actions recruits the same motor representations active during the actual execution of those same actions (Fadiga et al., 1995, Hari et al., 1998; for review see Rizzolatti and Craighero, 2004, Buccino et al., 2004a), and this in a somatotopic manner (Buccino et al., 2001). The mirror neuron system has been shown to be involved in imitation (Iacoboni et al., 1999) and imitation learning (Buccino et al., 2004a).
While motor imagery has been shown useful in sport practice and rehabilitation especially when combined with conventional rehabilitation treatment (Page et al., 2001), observation of actions has not yet been tested as a potential tool in neurorehabilitation.
The major aim of this study was to assess whether action observation therapy may lead to clinical improvement of motor impairment in chronic stroke patients, as measured by standard functional scales. Based on the findings of previous studies concerning the use of mental techniques in neurorehabilitation (Page et al., 2001), we combined action observation with the direct effects of action execution. Our hypothesis was that the activation of motor areas by action observation becomes reinforced by the concomitant active execution of the observed actions (Binkofski et al., 2004, Buccino et al., 2006). Additionally, by means of fMRI we studied the reorganization within the motor areas following this treatment, using an independent sensorimotor task consisting of object manipulation.
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Patients
Patients were recruited from the local Rehabilitation Centre. We excluded patients older than 76 years, with hemorrhagic stroke or ischemic lesions in the territory of posterior or Anterior Cerebral Artery, impaired level of consciousness (confusion, stupor, coma), severe to moderate aphasia, anosognosia or neglect, amnesia or dementia, depression.
After giving their informed consent fifteen patients (4 females) with a confirmed diagnosis of a first ever ischemic stroke in the territory of the
Clinical results
Each of the analyses was performed using the Wilcoxon signed ranks test. Age and duration of former therapies as the two most important demographic details revealed no significant difference between the treatment and the control groups (Wilcoxon signed rank test; see Table 1). In all patients the neurological impairment was stable as demonstrated by the lack of any significant difference between the results of the standard functional scales (WMFT, FAT) and the subjective self-assessment (SIS)
Discussion
There are two important findings in the present study. First, we could demonstrate that the new rehabilitation program combining action observation with intensive repetitive practice of the observed actions provides a significant improvement of motor functions, and this in chronic stroke patients with a well-established motor impairment of the upper limb. This improvement could be quantified in standard functional motor scales (WMFT, FAT) as well as in the subjective self-assessment of the
Acknowledgments
Supported by VW-Grants (I/79006 and I/81085) and BMBF-Grants (01GO0207 and 01GW0571).
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Both authors contributed equally to this work.