Activation studies of the motor system: in vivo investigations with PET and FMRI

Modern imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (FMRI) have improved our understanding of the functional organisation of the human brain. This article attempts to review in vivo activation studies focussed on central motor control. Specific patterns of cortical and subcortical activaton are reported in association with different aspects of motor behaviour, ranging from pure motor imagination to highly sophisticated performance of complex sequential motor actions. Moreover, data are presented supporting the notion of a functional segregation of human premotor cortical areas into distinct subcomponents. Possible roles of the basal ganglia, as integral parts of distributed cortico-subcortical motor loops, have emerged from pertinent imaging studies; in particular from those that define characteristics of motor processing via correlation analyses relating evoked regional cerebral blood flow (rCBF) responses to graded modulations of specific experimental parameters. (orig.)