Neuronal Correlates of Kinematics - to - Dynamics Transformation in the Supplementary Motor Area experience

addition, it was found that internal models for the dynamics are acquired independently of internal models for the kinematics, which subjects learn when the asso-Summary ciation between the visual stimulus and the instructed movement is perturbed (Krakauer et al., 1999; Flanagan It is widely acknowledged that movements are planned et al., 1999). Internal models for both the kinematics at the level of the kinematics. However, the central and the dynamics undergo consolidation in the hours nervous system must ultimately transform kinematic following acquisition. plans into dynamics-related commands. How, when, It has been suggested that the neuronal representa-and where the kinematics-to-dynamics (KD) transfor-tion of the internal models for the movement dynamics mation is processed represent fundamental and unan-may be partly stored in the cerebellum (Shidara et al., swered questions. We recorded from the supplemen-1993; Imamizu et al., 2000). However, processing of the tary motor area (SMA) of two monkeys as they dynamics occurs across multiple cortical and subcorti-executed visually instructed reaching movements. We cal areas. Numerous studies in monkeys have investi-specifically analyzed a delay period following the in-gated the dynamics-related activity of single neurons in struction but prior to the go signal (motor planning). different motor areas by comparing the activity recorded During the delay, a group of neurons in the SMA pro-in the absence of perturbation with that recorded in the gressively came to reflect the dynamics rather than presence of perturbing forces (or loads) to which the the desired kinematics of the upcoming movement. monkeys had adapted. These studies have found dy-This finding suggests that some neurons in the SMA namics-related neuronal activity during motor execution participate in the KD transformation. Reaching movements can be described at two different Werner et al., 1991), the ventral premotor area (PMv; levels: kinematics and dynamics. The term kinematics Hepp-Reymond et al., 1994), the putamen (Crutcher and refers to the evolution in time of the joint angles and Alexander, 1990), and the dentate and interpositus nu-hand position. The term dynamics refers to the set of clei of the cerebellum (Thach, 1978). In contrast, no forces exerted by the muscles. In Newtonian mechanics, dynamics-related activity was found in area 5 (Kalaska the causal relationship flows from dynamics to kinemat-et al., 1990). ics, that is, muscle forces cause hand movements. The Some of the motor areas displaying dynamics-related central nervous system, however, is faced with the inactivity during motor execution, such as the SMA and …