Somatoiopic studies on cerebellar fastigial cells

Summary The somatotopic inputs into fastigial cells have been studied in relation to cutaneous mechanoreceptors of forelimb and hindlimb. Some fastigial cells were very discriminative, not only in respect of the limb, but also to restricted areas of hairy skin and related toe pads. Others were much less so, forelimb and hindlimb cutaneous receptors evoking similar excitatory-inhibitory responses. In addition, from the contralateral hindlimb, responses were evoked which were comparable with those from the ipsilateral limb.Somatotopic diagrams have been constructed which show in four experiments the sites of fastigial cells in the parasagittal plane of the microelectrode tracks. For each experiment four separate plottings give a comparison of the sizes of responses evoked for forelimb and hindlimb: excitation from nerve volleys; inhibition from nerve volleys; excitation from pad taps; inhibition from pad taps. In this way it is shown that fastigial cells with similar somatotopic relations often occur in clusters, particularly when assessed by their inhibitory responses.Since fastigial inhibition is largely due to Purkyn cells, there is an attempt to correlate the somatotopic relations of Purkyn cells with the somatotopy of fastigial cell inhibition. The excitation of fastigial cells exhibits less somatotopic discrimination, which conforms with the poor somatotopic discrimination of cells of the lateral reticular nucleus.In a final discussion there is consideration of two principal projections from the vermis of the anterior lobe: Purkyn cells inhibiting Deiters neur; Purkyn cells inhibiting fastigial cells which in turn monosynaptically excite Deiters neurones, the inhibition of Deiters neurones being then by disfacilitation. The degree of forelimb-hindlimb convergence in these pathways is reconsidered and is diagrammatically illustrated.