The role of dorsal stream for motor imagery process. An ERP analysis

Objective: It has been argued that cortical motor system is shaped of many anatomical and functional distinctive sites (Rizzolatti, Luppino, 2001). Posterior parietal region is fundamental for sensory-motor transformations oriented to action’s execution: this assumption has to envisage the role of dorsal stream which is involved in the analysis of visual movement and monitoring of action. This work has analized the relation between motor imagery process (MI) and motor representation which is essential for our action and analysable by the former (Jeannerod, 1994). We used a MI task which entailed the production of mental motor images of everyday acts shared according to the part of the body involved in the execution. Participants and Methods: 25 subjects were tested by using an ERP procedure. We thought of an epoch of 400 ms (-100/300) in order to probe late movement-related cortical potentials and cognitive components of MI. Results: ERP variations were submitted to repeated measures analysis of variance. ANOVA showed a pre-motion positivity (PMP) localized within the fronto-central sites and a negative motor potential (MP) prior to the onset, with its maximum over the occipital areas. Besides, we found a negative peak at about 100 msec after the onset, more localized within parieto-occipital sites and a positive deflection at about 285 ms after the onset, with its maximum over the fronto-central areas. Conclusions: The results were read in the light of spatial representation systems of the action and taking into account the role of frontal and parietal lobes for the generation, maintenance and modification of mental motor images.