The visual-oculomotor striatum of the cat: functional relationship to the superior colliculus

The visual-recipient sector of the cat striatum receives corticostriate input from over 15 higher visual and oculomotor-related areas of the cortex and appears homologous with the physiologically characterized region of mixed visual and oculomotor inputs within the primate caudate nucleus. This area in the cat involves the dorsolateral caudate and a strip of the caudal putamen. In a first series of experiments, the former was injected with a retrograde tracer in several cats. Thalamostriate cells were found in extensive regions, including the intralaminar nuclei, certain motor-related nuclei, and, most notably, across much of the extrageniculate visual thalamus. In another set of experiments, anterograde tracers were also injected into the superior colliculus (SC), and labeled tectothalamic fibers were observed in all thalamic sites projecting to the visual-recipient striatum. These findings highlight for the first time the need for the SC to be considered in models of thalamostriate and visual/oculomotor-striatal function(s). Moreover, the data bring to light the fact that basal-ganglia outflow reaching the SC via striatonigro-nigrotectal circuitry is well positioned to modulate ascending tecto-thalamic-thalamostriatal signals destined for the visual-recipient striatum.