THALAMOCORTICAL ORGANIZATION IN THE CEREBELLO-THALAMO-CORTICAL SYSTEM

In the cat, the cerebellum projects via the ventroanterior-ventrolater al (VA-VL) complex of the thalamus to the motor and premotor cortices and also to the parietal association cortex. Cerebellar inputs to each of these regions have been characterized electrophysiologically by de pth profiles of cortical potentials following stimulation of the brach ium conjunctivum and of the VA-VL complex, and morphologically by the laminar distribution of thalamocortical (TC) terminations, in aggregat e and at the single-axon level. One population of TC neurons terminate d mainly in layer I and was associated with late surface negative pote ntials. A second population, with terminations in layers III and IV, w as associated with early deep negative potentials. Terminations in lay er III of the motor cortex formed multiple patches about 1-1.5 mm wide (mediolateral), which aligned to form 2-5 mm stripes extended rostroc audally. This pattern correlates with the configuration of individual TC axons, which have two to six separate terminal patches distributed over 6 mm (rostrocaudal). The wide morphological divergence of single TC axons in the cortex may imply functionally multiple innervation of different efferent columns. Alternately, along with other inputs, it m ay permit a highly dynamic output selection from multiple representati ons, for example, of a variety of muscle groups in different combinati ons.