This commentary is on the original article by Kirkpatrick et al. on pages 1049–1056 of this issue. Observing the movements of another person activates the mirror neuron system. This network of specialized neurons, that discharge either when performing or observing an action, is mainly distributed in the human premotor and parietal cortex. The mirror neuron network is believed to play an essential role in understanding the actions of others, as well as in our capacity to learn by imitation. Action observation therapy is basically a backdoor approach to improve motor (re)learning, allegedly by tapping directly into the mirror neuron system and activating cortical areas which strongly overlap those involved in movement execution.1 In order to facilitate motor learning, action observation therapy typically relies on repeated phases of observation of goal-directed actions followed by their execution. There is increasing evidence for the efficacy of this method in adults with hemiplegia during the subacute and chronic phases of stroke.2 In their trial, which addresses the efficacy of action observation therapy in children with unilateral cerebral palsy (CP), Kirkpatrick et al.3 demonstrate that there is no added-value of action observation over repetitive motor training, in a home-based, parent-delivered variant of the approach. This contrasts with a previous randomized trial in children with unilateral CP by Sgandurra et al.,4 which had shown significant improvements in bimanual function following more intensive, therapist-delivered, action observation therapy. Are these divergent findings due to differing settings and interventions in both studies, or could there be a more fundamental issue about applying action observation to children with early brain lesions? Kirkpatrick et al.3 adopted a pragmatic approach to intervention delivery. In the action observation group, children were repeatedly provided with the opportunity to imitate the motor tasks shown by their parents; whereas those in the control group repeated identical goal-directed tasks for the same time, without the opportunity to imitate their parents. Both groups improved similarly. In Sgandurra et al.'s4 earlier study children in the action observation group watched videos of the actions they were then expected to perform, while those in the control group watched video-games. The action observation group fared better. If this does indicate an intrinsic value of action observation above observing unrelated actions in improving motor performance, the study by Kirkpatrick et al. seems to show that improvements are similar if the time spent observing a movement is actually used to execute the movement. Can all children with unilateral CP be considered responsive to action observation? Indeed if brain lesions have affected the core circuitry of the mirror neuron network, i.e. the premotor and/or parietal cortex and/or their connections, action observation therapy could prove pointless. A functional magnetic resonance imaging study including 18 children with unilateral CP and either cortical or sub-cortical lesions showed that observation of hand movements engaged the motor observation and execution network, regardless of the degree of motor impairment or lesion localization.1 Consequently, a majority of children with unilateral CP might be expected to respond to action observation. To what degree does the activation of the mirror neuron system, based on movement observation, contribute to consolidate motor programmes? A notable study on professional ballet dancers, who based on their sex were familiar or unfamiliar with performing specific moves, demonstrated that mirror circuits have a pure motor response over and above visual representations of movements.5 Mirror system activity seems to depend on possessing the motor representation for an observed action, or in other words on being familiar with performing the movement. The efficacy of action observation therapy in adults after stroke may rely on the remains of their motor observation and execution networks, constituted through a lifetime of repeated normal motor experiences. Children who have never experienced the competent and normal movement patterns that they observe may not have quite the same ability to mimic activities in their mirror neuron systems. In all studies of action observation therapy for unilateral CP, children watched motor tasks performed by expert models. It may be that a shift towards observing less expert learning models (such as other children or even peers with a similar movement disorder) could provide a larger keyhole into their mirror systems. If for the time being action observation should be used cautiously in children, further research may provide refinements that may considerably increase its ability to tap into the developing mirror neuron system.
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Sep 1, 2016
Matthew A Wyon + 5
Open Access
