Do single motor cortical cells explicitly encode intrinsic variables of movement?
The present findings reveal that the discharge of many single MI neurons located in the bank of the central sulcus covaried with arm orientation during planar reaching movements. Mathematical models of units encoding intrinsic joint-centered kinematic or kinetic parameters predicted a complex relationship between changes in arm orientation and changes in directional tuning that had many similarities to those observed for motor cortical cells, whereas the extrinsic hand space model predicted very little change of directional tuning of single cells with arm orientation. Therefore this study shows that motor cortical discharge during reaching movements is influenced by arm geometry, and any coordinate system proposed for the movement representation in motor cortex that does not take into account the geometry of the arm provides an inadequate description of the activity of most single MI cells. However, the results are not proof that MI neurons encode movement either explicitly or exclusiv
