The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase. V. The posterior lobe vermis and the flocculo-nodular lobe.

The cerebellar corticonuclear and nucleocortical connections of the posterior lobe vermis and the flocculonodular lobe were studied in the cat by means of anterograde and retrograde transport of horseradish peroxidase. The main terminal area for corticonuclear fibres from the posterior lobe vermis is the ipsilateral fastigial nucleus. A mediolateral topography is indicated: midvermal regions project to the medial part of the fastigial nucleus, more lateral regions project to the lateral part of the fastigial nucleus. A rostrocaudal arrangement is also present, the anterior folia of the posterior lobe vermis projecting to the caudalmost part of the fastigial nucleus while more posterior folia project slightly more rostroventrally. Corticonuclear fibres from the flocculus terminate in an almost continuous band extending through the ipsilateral dentate nucleus and into the posterior interposed nucleus (through the nuclear regions previously designated cerebellar zones D2, D1 and C2). With few exceptions the nucleocortical connection shows the same arrangement as the corticonuclear, giving further evidence for a corticonuclear-nucleocortical reciprocal relationship. These and other observations are discussed and related to previous observations on the corticonuclear and nucleocortical cerebellar projections.