The organization of cortical activity in the anterior lobe of the cat cerebellum during hindlimb stepping.

We recorded from over 280 single cortical neurons throughout the medial anterior lobe of the cat cerebellum during passive movements of the hindlimbs resembling stepping on a moving treadmill. We used three stepping patterns, unilateral stepping of either the ipsilateral or contralateral leg and bipedal stepping in an alternating gait pattern. We found that over 60% of the neurons, mostly Purkinje cells, responded to stepping of one or both legs, and over 40% to more than one type of stepping pattern. Responsive cells were distributed throughout the five anterior lobules, and the highest concentration was found in traditional hindlimb areas in lobules 2 and 3. A comparison of response waveforms showed that they are similar for neighboring cells in many parts of the cerebellar cortex, and they tend to form local blob-like groupings. Response patterns, i.e., relationship among responses to each stepping type, tended to be similar within a local group. The groupings extend further in the parasagittal dimension (up to about a third of a lobule) than in the transverse dimension (about 1 mm), and they may form functional modules. A principal component analysis also showed that the responses were composed of a four basis waveforms (principal components) that explained about 80% of the response waveform variance that were nearly identical to those derived from dorsal spinocerebellar tract (DSCT) responses to similar stepping movements. We reconstructed the locations of the recorded neurons on a 2D map of the cerebellar cortex showing the spatial distribution of responsive cells according to their response characteristics. We propose, on the basis of these results, that the sensory input to the cerebellum from the hindlimbs is distributed to multiple zones that may each contribute to a different component of cerebellar function.