Impaired motor imagery in right hemiparetic cerebral palsy

It is generally assumed that movements of a part of the body (e.g., hands) are simulated in motor imagery (MI) tasks. This is evidenced by a linear increase in reaction time as a function of the angular rotation of the stimulus. Under the assumption that MI plays a critical role for anticipatory motor planning, which is known to be impaired in individuals with right hemiparetic cerebral palsy (right HCP; left congenital brain damage), but to a lesser extent in individuals with left HCP, we hypothesized that MI is impaired in the participants with right HCP. In the present study, 8 participants with right and 11 participants with left congenital brain damage and 9 neurologically healthy controls were presented with two MI tasks to study this supposed relation between hemispheric processes and behaviour. Participants were instructed to make a laterality judgment on the basis of displayed pictures of hands (either holding a hammer or not) presented in different orientations. For both the control group and the left HCP group, a linear increase in reaction time as a function of angle of rotation was found. Interestingly, no such relationship was observed for the right HCP group, suggesting a disorder in MI for these participants. Collectively, these findings provide new insights into the cause of the anticipatory planning deficits in right HCP individuals.