Command of visually guided 3D arm movements by the cerebral cortex

A two-layered network model which learns and performs two-joint arm reaching movements in 3-D space and is consistent with neurobiological data on cell activities recorded in the motor cortex during these movements is proposed. These experimental results show that: (1) neurons which command muscle synergies are broadly tuned to preferred directions in the 3-D space, (2) the cell´s preferred direction rotates with the initial position of the arm, and (3) the rotation of the arm in space and the rotation of the whole population of preferred directions are highly correlated. The motor cortex is thus working in an arm centered coordinate system, and the available visual information about the desired trajectory should be translated in this coordinate system for the appropriate command of the arm. The authors show how this computation can be performed by processing units which model the properties of the cortical column as the basic neuronal circuits common to all cortical areas