Cortical afferents and internal connectivity of the superior colliculus in the domestic cat (visual cortex, oculomotor)
Description
The projections of frontal cortical oculomotor areas and visual cortical areas to the superior colliculus, as well as projections from the superficial to the deep collicular compartments, were examined in the domestic cat using the retrograde transport of WGA-HRP/HRP. The following observations were made. (1) Large, intermediate, and deep collicular injections consistently result in the retrograde labeling of neurons in frontal cortical oculomotor areas previously suggested as analogous to the frontal eye fields (FEF) of the monkey. (2) Large injections involving all collicular layers consistently result in the retrograde labeling of neurons within numerous visual cortical areas. In contrast, small laminar injections are associated with specific patterns of retrograde cortical labeling depending on the location of the injection site in either the superficial or deep collicular compartments. Specifically, following injections restricted to the superficial grey layer, the heaviest labeling is found in the primary visual cortical areas located in the caudal-most regions of the cerebral cortex. With increasingly more ventral placement of small restricted injections of WGA-HRP/HRP, the majority of labeled neurons are seen in progressively more rostral areas of neocortex, while the labeling in caudal cortical areas becomes diminished. These data support the view that visually responsive neurons in the intermediate and deep grey layers of the superior colliculus in the cat receive visual information from extensive extrastriate visual cortical areas. (3) Following the placement of small injections of WGA-HRP/HRP within the intermediate and deep laminae of the superior colliculus, retrogradely labeled neurons are found in all collicular layers dorsal to the injection site. Specifically, injections placed within the intermediate grey layer result in the retrograde labeling of large numbers of neurons in the superficial grey and optic layers. The majority of labeled neurons following deep injections are observed in the intermediate grey layer, and the number of labeled superficial neurons decreases with increasing depth of the injection site. These observations confirm and add new data to previous evidence supporting the view that visual information reaching the superficial collicular layers can be transmitted to the deep compartment via interlaminar connections. (Abstract shortened with permission of author.)