Mossy and climbing fibre organization on the anterior lobe of the cerebellum activated by forelimb and hindlimb areas of the sensorimotor cortex

Stimulation of forelimb and hindlimb areas of the sensorimotor cortex in the cat evokes in the lobus anterior of the cerebellum an early response at latency of 3–3.5 msec due to the mossy fibre input (MF) and a later response at latency of 13–16 msec due to the climbing fibre (CF) input. In the pars intermedia these two types of responses are organized in a somatotopic manner: the hindlimb area projects in lobuli HIV and HIII whereas the forelimb area projects to lobulus HV. In the vermis a somatotopic arrangement is less clear. Both forelimb and hindlimb areas of the sensorimotor cortex project to lobuli III, IV and V: on a maintained somatotopy in a caudo-rostral direction there is a tendency for the hindlimb area of the sensorimotor cortex to be well represented in a longitudinal strip close to the paravermal sulcus. This arrangement in the vermis is evident for the CF pathways, but more difficult to demonstrate for the MF pathways. The forelimb area of the sensorimotor cortex projects to those areas of the lobus anterior impinged upon by the forelimb nerves through both the MF and CF systems and the same holds true for the hindlimb area and the hindlimb nerves.