Mapping 3D sensory inputs onto spinal interneurons

Extracellular recordings of 43 spinal interneurons were performed in the decerebrate cat while its hindlimb was manipulated in 3 dimensional space with a 6-degree of freedom robotic arm. Internal/external rotations, toe in/toe out and flexion/extension movements were performed about the ankle joint. Peripheral nerve stimulation was used to categorize cells by field potential threshold into gr Ila and gr II types. 80% (16/20) of the gr la cells showed firing frequency changes to less than half of the rotations imposed by the robot and only 20% to more than half. 39% (9/23) of the gr II cells showed responses to less than half of the imposed movements and 61% (14/23) of the gr II cells responded to more than half of the imposed movements.