Cerebellar cortical activity in the cat anterior lobe during hindlimb stepping.

We recorded from over 250 single cortical neurons throughout the medial anterior lobe of the cat cerebellum during passive movements of the ipsilateral hindlimb resembling stepping on a moving treadmill. We applied three different quantitative analysis techniques to determine the extent of neuronal modulation that could be accounted for by the stepping movements. The analyses all indicated that up to half the recorded neurons in all five lobules responded to these passive hindlimb movements. We reconstructed the locations of the recorded neurons on a 2-D map of the cerebellar cortex in order to determine the spatial distribution of responsive cells. Cells that were located in the classical hindlimb projection areas of the anterior lobe (in lobules 2 and 3) were generally most responsive to the limb movement with activity patterns that generally had a linear relationship to hindlimb kinematics. Cells in lobules 4 and 5, considered as classical forelimb areas of the cerebellum, were also responsive. Although these cells tended to have noisier firing patterns, many were found to be modulated nevertheless by the hindlimb movements. We also found a clear demarcation between zones b and c, with a higher fraction of responsive cells in all lobules located in zone b.