Aim: 

This study was designed to examine the changes in the modulation of Interpositus nucleus cells during continuous movements of the forelimb.

Methods: 

We used a robot to move the forelimb of anesthetized rats through the circular and figure-8 trajectories, in a parasagittal plane. Extracellular recordings from 151 cells provided the basis for multiple regression analysis where the firing discharges of single cells were related to the velocity and its vectorial components, that is movement speed and direction.

Results: 

We found that the majority of neurons showed a combinatorial representation of the movement velocity (61%). However, a significant fraction of the neuronal population was modulated only by movement speed (26%) with a smaller number of units whose activity was related to the directional component alone (13%). Most of the neurons modulated by the speed were located in the posterior interpositus nucleus whereas the anterior portion enclosed mainly the representation of the full velocity vector.

Conclusion: 

The finding imply that sensory information related to whole limb movement velocity is encoded in the interpositus nucleus and indicated that the posterior interpositus may specifically represent movement speed.