Parieto-frontal circuitry in visuomotor control

One of the fundamental questions in cognitive neuroscience is the question how sensory cues influence the motor system. This thesis investigates how different circuits in the brain allow visual information to reach the motor system, with a particular focus on the role of parieto-frontal circuits in visuomotor associative learning and manual prehension. In the first part of this thesis we studied visuomotor associative learning in healthy participants with functional MRI and psychophysics. The findings in these chapters (chapter 2 and 3) led us to conclude that the performance of overlearned visuomotor associations does not only rely on frontostriatal circuits for deciding what action to perform in a certain context, but also on the posterior parietal cortex to determine how actions are performed. In the second part of this thesis visually-guided grasping movements were studied with functional MRI and an analysis of effective connectivity, Dynamic Causal Modelling. These first chapter in this part (chapter 4) shows that it is feasable to study ecologically valid reach-to-grasp movements in a scanner environment. Chapter 5 argues against a strict dichotomy between the cerebral control of reaching and grasping along dorsoventral and dorsomedial pathways, as suggested by the two visuomotor channel hypothesis (Jeannerod et al., 1995). Alternatively, it is suggested that the relevance of the dorsolateral and the dorsomedial circuits for prehension is a function of the degree of on-line control required by the movement. Crucially, the results of chapter 5 clearly show how important it is to investigate the brain from a systems-level perspective and explore the functional interactions between brain areas by methods of effective connectivity. In the concluding chapter a summary of the results is presented, together with the major conclusions of the thesis