Ventral and dorsal fiber systems for imagined and executed movement

Although motor imagery is an entirely cognitive process, it shows remarkable similarity to overt movement in behavioral and physiological studies. In concordance, brain imaging studies reported shared fronto-parietal sensorimotor networks commonly engaged by both tasks. However, differences in prefrontal and parietal regions point toward additional cognitive mechanisms in the context of imagery. Within the perspective of a general dichotomization into dorsal and ventral processing streams in the brain, the question arises whether motor imagery and overt movement could differentially involve the dorsal or ventral system. Therefore, we combined fMRI and DTI data of 20 healthy subjects to analyze the anatomical characteristics of connecting fronto-parietal association pathways of imagined and overt movements. We found a dichotomy of fiber pathways into dorsal and ventral systems: the superior longitudinal fascicle (SLF II-III) was found to connect frontal and parietal regions involved in both overt and imagined movements, whereas a ventral tract via the extreme/external capsule (EmC/EC) connects cortical regions specific for motor imagery that were situated more anteriorly and posteriorly. We suppose that motor imagery-related kinesthetic emulations are embedded into dorsal sensorimotor networks, and imagery-specific cognitive functions are implemented in the ventral system. These findings have implications for models of motor cognition.