Abstract
Both motor imagery and mirror training have been used in motor rehabilitation settings to promote skill learning and plasticity. As motor imagery and mirror training are suggested to be closely linked, it was hypothesized that mirror training augmented by motor imagery would increase corticospinal excitability (CSE) significantly compared to mirror training alone. Forty-four participants were split over two experimental groups. Each participant visited the laboratory once to receive either mirror training alone or mirror training augmented with layered stimulus response training (LSRT), a type of motor imagery training. Participants performed 16 min of mirror training, making repetitive grasping movements paced by a metronome. Transcranial magnetic stimulation (TMS) mapping was performed before and after the mirror training to test for changes in CSE of the untrained hand. Self-reports suggested that the imagery training was effective in helping the participant to perform the mirror training task as instructed. Nonetheless, neither training type resulted in a significant change of TMS map area, nor was there an interaction between the groups. The results from the study revealed no effect of a single session of 16 min of either mirror training or mirror training enhanced by imagery on TMS map area. Despite the negative result of the present experiment, this does not suggest that either motor imagery or mirror training might be ineffective as a rehabilitation therapy. Further study is required to allow disentangling the role of imagery and action observation in mirror training so that mirror training can be further tailored to the individual according to their abilities.
Highlights
Mirror training was successfully introduced in the 1990s to alleviate phantom limb pain in amputees (Ramachandran and Rogers-Ramachandran, 1996)
The aim of this study was to explore whether mirror training augmented with motor imagery training would significantly increase changes in Transcranial magnetic stimulation (TMS) map area compared to mirror training alone
The results show a single session of 16 min of mirror training does not lead to significant changes in TMS map area
Summary
Mirror training was successfully introduced in the 1990s to alleviate phantom limb pain in amputees (Ramachandran and Rogers-Ramachandran, 1996). In mirror training a mirror is placed in front of the participant in a parasaggital plane with each limb, e.g., hand or foot, positioned on either side of the mirror. When one limb is moved whilst watching its mirror reflection, the visual illusion is created that the passive limb behind the mirror is moving. With repetitive practice this has been found to lead topographic reorganization of the somatosensory cortex, in the hemisphere associated with the amputated limb (for review Ramachandran and Altschuler, 2009). The positive outcomes associated with mirror training have been attributed to its close correspondence to motor imagery and action observation (Stevens and Stoykov, 2003; Vogt et al, 2013). Physical practice has long been considered essential in motor learning and rehabilitation (e.g., Butefisch et al, 1995), these findings might suggest imagery and action observation are valuable complements
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