Rüdiger J. Seitz · Klaus Martin Stephan, Ferdinand Binkofski.
Conscious control of action involves the voluntary initiation and the continuous adjustment of motor activity. Neuroimaging data provide evidence that the plan for a movement is developed with respect to the behavioral context in prefrontal cortex, while the synergies of a motor program are coded by premotor cortex and the specific movement parameters by the motor cortex. It is suggested that the initiational aspects of conscious motor activity are implemented in a medial system of information flow and the integrative aspects in a lateral system of the human frontal lobe.
The frontal lobe comprises the motor cortex, the premotor cortex, and the prefrontal cortex, which all contribute to executive functions. The executive functions can be conceptualized as a hierarchical system of action control comprising volition, planning, selection, programming, and performance of movement. An intentional system allows movements to be voluntarily selected and initiated. The intended movement has to be imbedded in the behavioral context and planned accordingly. Further, movement synergies have to be programmed to generate a desired action. Finally, movement parameters have to be specified in relation to the physical state of the subject to allow for automatic performance. Neuroimaging methods open avenues to disentangle the cerebral structures involved in the different aspects underlying executive functions. Here, we were interested in three different processes of movement control. Using simple finger movements of both hands, we wished to identify the brain structures controlling bimanual actions. Specifically, subjects were required to adjust simultaneous or alternating movements with both hands in a self-paced manner to each other. In a second experiment, we were interested in mapping the cortical representations of movements in space. A third study aimed at identifying the cortical areas involved in temporal control of movements. We will describe that these motorcontrol tasks share common, but also involve different subareas of the premotor and prefrontal cortex in the human frontal lobe. These findings will be supplemented by studies in patients showing the critical importance of some of these subareas both for movement performance and recovery.