CEREBELLAR AND CEREBRAL INPUTS TO CORTICOCORTICAL AND CORTICOFUGAL NEURONS IN AREA-5 AND AREA-7 IN THE CAT

1. In the parietal cortex (Px, areas 5 and 7), the organization and characteristics of cerebellar and cerebral inputs and their effects on efferent neurons were investigated with the use of intracellular and extracellular recording techniques in the anesthetized cat. 2. Evoked field potential analysis revealed that two regions of the Px, the caudal bank of the ansate sulcus (Ans. S.) and the crown of the suprasylvian gyrus (Ssyl. G.), received converging input from the dentate and the interpositus nucleus. The cerebellar input to the caudal bank of the Ans. S. was relayed via the ventrolateral region of the ventroanterior-ventrolateral (VA-VL) complex of the thalamus, whereas the cerebellar input to the crown of the Ssyl. G. was relayed via the dorsomedial region of the VA-VL complex. 3. A total of 176 neurons was recorded intracellularly in the Pr to examine inputs from the cerebellum. Of these, 72 neurons were corticocortical neurons projecting to the motor cortex (Mx), and 48 were corticofugal neurons to the pontine nucleus (PN). Intracellular staining with horseradish peroxidase revealed that the former corticocortical neurons were layer III pyramidal neurons and the latter corticofugal neurons were layer V pyramidal neurons. 4. Stimulation of the brachium conjunctivum (BC) produced di- or polysynaptic excitatory postsynaptic potentials (EPSPs) in corticocortical neurons projecting to the Mx and corticofugal neurons to the pontine nucleus in the Px. The characteristics of BC-evoked EPSPs were different between the bank of the Ans. S. and the crown of the Ssyl. G. In the bank of the Ans. S., the slope of the rising phase of the BC-evoked EPSPs was steeper, and their minimum latency was shorter by 0.8 ms than those in the crown of the Ssyl. G. These differences may reflect differences in the terminal distribution and conduction velocity of the thalamocortical fibers relaying cerebellar input to these two parietal areas. 5. Stimulation of the Mx produced mono- or disynaptic EPSPs in both corticocortical neurons projecting to the Mx and corticofugal neurons projecting to the pontine nucleus in the Px. For each neuron, effective sites for inducing EPSPs were distributed very widely and sometimes covered both areas 4 and 6. Extensive corticocortical projection from the Mx to the Px was confirmed by injection of an anterograde tracer into the Mx. 6. These data indicate that neurons in the Px receive inputs from both the cerebellum and the Mx and send outputs to the Mx and the cerebellum. This input-output organization puts the Px in a good position to integrate feed-forward motor output signals from the Mx and the cerebellum and feedback sensory information from the periphery for adequate voluntary movement.