Abstract
Internal models are neural mechanisms that can mimic the input-output properties of musculoskeletal systems and external objects. I'll summarize our series of functional neuroimaging studies on internal models and focus on two issues: 1) modular organization of internal models for tool use, and 2) their contributions to coordinative movements. Regarding the first issue, we investigated cerebellar activity when human subjects learned how to use a novel tool (the cursor of a rotated mouse that appears in a rotated position), and found that after learning, activity reflecting an internal model of the tool increased in the lateral cerebellum. We also investigated internal model activity after sufficient training for the use of two types of novel tools (the cursors of a rotated mouse and a velocity mouse whose velocity is proportional to the mouse position), and found that cerebellar activity for the two tools was spatially segregated and that overlap was very small. These results indicate that internal models in the cerebellum are acquired in a modular fashion. For the second issue, we investigated brain activities under two kinds of tasks: coordination between eye and hand tracking movements and coordination between grip and load force during object manipulation. We found that the cerebellar activity increases more in both coordinative tasks than in independent tasks. These studies suggest that internal models represent input-output properties of different controlled objects and contribute to their coordinative control. [Jpn J Physiol 55 Suppl:S20 (2005)]
