Your mind's hand: motor imagery of pointing movements with different accuracy

Jeannerod (2001) postulated that motor control and motor simulation states are functionally equivalent. If this is the case, the specifically relevant task parameters in online motor control should also be represented in motor imagery. We tested whether the different spatial accuracy demands of manual pointing movements are reflected on a neural level in motor imagery. During functional magnetic resonance imaging (fMRI) scanning, 23 participants imagined hand movements that differed systematically in terms of pointing accuracy needs (i.e., none, low, high). In a low-accuracy condition, two big squares were presented visually prior to the imagery phase. These squares had to be pointed at alternately on a mental level. In the high-accuracy condition, two little squares had to be hit. As expected on the basis of speed-accuracy trade-off principles, results showed that participants required more time when accuracy of the imagined movements increased. The fMRI results showed a stepwise increase in activation in the anterior cerebellum and the anterior part of the superior parietal lobe (SPL) with rising accuracy needs. Moreover, we found increased activation of the anterior part of the SPL and of the dorsal premotor cortex (dPMC) when imagery included a square (i.e., in the low- and high-accuracy conditions) compared to the no-square condition. These areas have also been discussed in relation to online motor control, suggesting that specific task parameters relevant in the domain of motor control are also coded in motor imagery. We suggest that the functional equivalence of action states is due mostly to internal estimations of the expected sensory feedback in both motor control and motor imagery.