Cortical networks for motion processing: effects of focal brain lesions on perception of different motion types.

Neuropsychological studies in humans provide evidence for a variety of extrastriate cortical areas involved in visual motion perception. Multiple mechanisms underlying processing of different motion types have been proposed, however, support for cortical specialization has remained controversial so far. We therefore studied motion perception in 23 patients with focal lesions to various cortical areas and considered translational motion, heading from radial flow, as well as biological motion. Patients' detection thresholds were compared with age-specific data from a large healthy control sample (n=122). Elevated thresholds and significant threshold asymmetries between both visual hemifields were defined as deficits. Contrary to prevalent opinion, we found a high prevalence of motion deficits in our sample. Impairment was restricted to a specific motion type in 10 patients, whereas only a single patient showed a deficit for multiple motion types. Functional areas were determined by lesion density plots and by comparison between patients with and without a specific deficit. Results emphasize a dissociation between basic motion processing and processing of complex motion. Anatomical analysis confirmed critical occipito-temporo-parietal areas for perception of translational motion. In contrast, heading perception from radial flow proved to be remarkably robust to most lesions. We exclusively identified the frontal eye fields as a critical structure. Biological motion perception relied on distinct pathways involving temporal, parietal, and frontal areas. Although precise functional roles of identified areas cannot be determined conclusively, results clearly indicate regional specialization for motion types of different complexity. We propose a network for motion processing involving widely distributed cortical areas.