Termination and functional organization of the dorsolateral spino-olivocerebellar path.

1. Pathways ascending in the lateral funiculus of the spinal cord and terminating as climbing fibres in the anterior lobe of the cerebellum have been investigated in decerebrate cats with the cord partially transected in the third cervical segment, sparing only part of the left lateral funiculus. The climbing fibre responses evoked in Purkinje cells by electrical stimulation of peripheral nerves were studied by recording from single cells and by recording the mass activity at the cerebellar surface.2. Two pathways have been distinguished. One ascends through the dorsal part of the lateral funiculus and relays in the inferior olive. It is denoted the dorsolateral spino-olivocerebellar path (DLF-SOCP) and forms the subject of this paper. The other path occupies in part a more ventral position in the lateral funiculus and it is not known if it relays in the inferior olive. It is denoted the LF-CF-SCP (lateral funiculus-climbing fibre-spinocerebellar path).3. The DLF-SOCP is activated predominantly by cutaneous afferents from restricted areas in the ipsilateral paws. The relay in the spinal cord is almost certainly monosynaptic, but a long delay in the brain stem suggests that the path is interrupted by several synapses at this level. The pathway terminates in the pars intermedia in sagittal zones with a somatotopical organization (Fig. 12).4. Components of the DLF-SOCP and the dorsal spino-olivocerebellar path converge onto the same olivary neurones which project to the pars intermedia and it is concluded on this evidence that the DLF-SOCP also relays in the inferior olive.5. The DLF-SOCP is compared with the other known spinocerebellar paths terminating as climbing fibres in the anterior lobe. The functional role of these paths and the general significance of the sagittal projection patterns are discussed.