AbstractMovement imagery (MI) is a cognitive motor process that shares neural networks with movement execution and observation. Previous research using transcranial magnetic stimulation (TMS) has demonstrated that both physical and observational training can elicit motor-cortical adaptations in the representation of movement (e.g. Classen et al., 1998; Stefan et al., 2005). This same effect has recently been demonstrated with MI (Yoxon & Welsh, submitted). These changes are thought to occur because the training potentiates (increases the excitability of) the representation of the trained movement. In support of this account, a positive relationship was reported between the magnitude of motor adaptations following observational training and the magnitude of corticospinal activation during action observation (i.e. the difference in amplitude of motor evoked potentials [MEPs] between rest and during an instance of action observation). The current experiment assessed this same relationship with MI training. The dominant direction of TMS-evoked thumb movements (i.e. flexion or extension) was determined before and after training. Single-pulse TMS was also used to determine the amplitude of MEPs during imagined flexion and extension of the thumb. During the training session, participants imagined themselves moving their thumb in the opposite direction of the pre-determined dominant direction. A strong positive relationship was found between corticospinal excitation during MI and both the change in the proportion of movements in the training direction. Consequently, it appears that the activation of the corticospinal system is strongly related to motor adaptations following MI training.
Acknowledgments: This research was supported by grants and scholarships from the Natural Sciences and Engineering Research Council of Canada