Zonal termination of the tecto-olivocerebellar pathway in the cat.

The climbing fibre pathway from the tectum to posterior cerebellar cortex was investigated in chloralose anaesthetized cats. With low threshold electrical stimulation within the deeper layers of the superior colliculus, climbing fibre responses were recorded in a centrally located, longitudinal area of lobulus VII, oriented perpendicular to the long axis of the folia. This same area showed climbing fibre evoked activity regardless of the side of tectum stimulated. Hence, it was concluded that the tecto-olivocerebellar pathway terminates bilaterally in the most medial parts of the cerebellar cortex, the termination zones being denoted the al zones. The results were discussed in relationship to recent anatomical knowledge of the tecto-olivary proteins and of the olivocerebellar projection to lobulus VII, and indicate that descending paths from the brain stem to the inferior olive might "respect" its intrinsic compartmentalization.