Information processing in human parieto-frontal circuits during goal-directed bimanual movements.

It is known that, in macaques, movements guided by somatosensory information engage anterior parietal and posterior precentral regions. Movements performed with both visual and somatosensory feedback additionally activate posterior parietal and anterior precentral areas. It remains unclear whether the human parieto-frontal circuits exhibit a similar functional organization. Here, we employed a directional interference task requiring a continuous update of sensory information for the on-line control of movement direction, while brain activity was measured by functional magnetic resonance imaging (fMRI). Directional interference arises when bimanual movements occur along different directions in joint space. Under these circumstances, the presence of visual information does not substantially alter performance, such that we could vary the amount and type of sensory information used during on-line guidance of goal-directed movements without affecting motor output. Our results confirmed that in humans, as in macaques, movements guided by somatosensory information engages anterior parietal and posterior precentral regions, while movements performed with both visual and somatosensory information activate posterior parietal and anterior precentral areas. We provide novel evidence on how the interaction of specific portions of the dorsal parietal and precentral cortex in the right hemisphere might generate spatial representations by integrating different sensory modalities during goal-directed movements.

Internal vs external generation of movements: differential neural pathways involved in bimanual coordination performed in the presence or absence of augmented visual feedback.

It is commonly agreed that a functional dissociation with respect to the internal vs external control of movements exists for several brain regions. This has, however, only been tested in relation to the timing and preparation of motor responses, but not to ongoing movement control. Using functional magnetic resonance imaging (fMRI), the present study addressed the neuroanatomical substrate of the internal-external control hypothesis by comparing regional brain activation for cyclical bimanual movements performed in the presence or absence of augmented visual feedback. Subjects performed a bimanual movement pattern, either with the help of on-line visual feedback of the movements (externally guided coordination) or with the eyes closed on the basis of an internal representation of the movement pattern (internally generated coordination). Visual control and baseline rest conditions were also added. Results showed a clear functional dissociation within the network involved in movement coordination. The hMT/V5+, the superior parietal cortex, the premotor cortex, the thalamus, and cerebellar lobule VI showed higher activation levels when movements were guided by visual feedback. Conversely, the basal ganglia, the supplementary motor area, cingulate motor cortex, the inferior parietal, frontal operculum, and cerebellar lobule IV-V/dentate nucleus showed higher involvement when movements were internally generated. Consequently, the present findings suggest the existence of distinct cortico-cortical and subcortico-cortical neural pathways for externally (augmented feedback) and internally guided cyclical bimanual movements. This provides a neurophysiological account for the beneficial effect of providing augmented visual feedback to optimize movements in normal and motor disordered patients.