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The termination patterns in the cerebellar anterior lobe of one mossy fiber path, the exteroceptive component of the cuneocerebellar tract (E-CCT), and one climbing fiber system, the dorsal spino-olivocerebellar paths (DF-SOCPs), which both relay in the main cuneate nucleus, were compared in the cat. The E-CCT terminates in the ipsilateral half of the anterior lobe in five sagittal zones which overlap five of the eight zones activated from the DF-SOCPs. In at least one zone the E-CCT projection has a somatotopical organization which is similar to and overlaps that of the DF-SOCP.

The somatotopical organization of the projection through the dorsal spino-olivocerebellar path (DF-SOCP) to the c3 zone in the cerebellar anterior lobe was studied by recording climbing fiber field potentials in the cerebellar cortex evoked on stimulation of peripheral nerves. The c3 zone was shown to contain a detailed and systematic representation of the ipsilateral body half with the follwing characteristics: 1. Single nerves project to one or two sagittal strips of cortex which extend across several folia. The width of the strips varies between 0.2 and 1 mm and the length may be as long as 15-20 mm along the unfolded cortex. 2. The strips activated from different nerves occur in an order which usually follows the segmental innervation, the hindlimb being represented rostrally and the forelimb caudally in the zone. 3. The double representation of some nerves makes it possible to distinguish one medial and one lateral part of the c3 zone with the projection areas organized approximately as mirror images. Additional observations on other zones activated by the DF-SOCP system (Ekerot and Larson, 1979a) indicate that the c1 zone, has a somatotopical organization which is reminiscent of that of the c3 zone, whereas the x and d1 zones have different topographical organizations.

1. A pathway ascending in the lateral funiculus of the spinal cord and terminating as climbing fibres in the cerebellar anterior lobe has 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 were studied by recording from single cells and by recording the mass activity at the cerebellar surface.2. The pathway is activated by the flexor reflex afferents from all four limbs. It ascends in an area of the lateral funiculus which partly overlaps that of the dorsolateral spino-olivocerebellar path (Larson, Miller & Oscarsson, 1969) but also extends more ventrally. The pathway conducts relatively fast in the spinal cord and is considerably delayed in the brain stem suggesting several interneurones at that level. It projects to a narrow sagittal zone in lobule V of the pars intermedia (Fig. 4).3. It is not known if the pathway relays in the inferior olive and it has provisionally been denoted the LF-CF-SCP (lateral funiculus-climbing fibre-spinocerebellar path).4. The Purkinje cells were usually activated by the flexor reflex afferents from all four limbs with equal effectiveness. On natural stimulation responses were obtained on deep pressure of the limbs.5. The pathway and its functional significance are discussed.

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.