General plan of the thalamic projections to the prefrontal cortex in the cat.

This study elucidates the general pattern of the thalamocortical neurons which project to the prefrontal cortex (PfC) in the cat, on the basis of the findings obtained using different retrograde labeling techniques in a large number of animals. The injections of the retrograde tracers covered the whole extent of the PfC, and did not invade gray or white matter outside the intended targets. The labeled neurons formed a vertical paramedian band throughout the rostrocaudal extent of the thalamus. This band was densest at the mediodorsal and ventromedial nuclei regions, encroached upon neurons located more medially and laterally, and largely spared the intralaminar nuclei. There were overlaps between neuron populations projecting to different subdivisions of the PfC, or to the PfC and sectors of the motor, insular, limbic and anterior ectosylvian sulcus cortices. However, these projections to separate cortical subdivisions apparently arise from different neuron clusters, with little collateralization of the axons arising from a single thalamocortical neuron. Only the neurons of the ventromedial nucleus, seem to possess somewhat more widespread terminal axons in the cortex.