Mapping Projections from Superior Colliculus to Frontal Orienting Field Through the Mediodorsal Nucleus in Thalamus

Abstract

Decision making is a complicated process that has been considered to follow an accumulation of evidence model. Interactions with the world accumulate and provide evidence to favor one decision ut of numerous possibilities. Previous studies conducted in rats have shown that the frontal orienting fields (FOF), homologous to the primate frontal eye fields (FEF), as well as the SC can affect the decision making process and are strongly implicated in evidence accumulation. Studies in both primates and rodents have revealed a direct monosynaptic descending pathway from FOF/FEF to SC. While the reverse has not been found, studies in primates have revealed an ascending disynaptic pathway from SC to FEF through the mediodorsal nucleus (MD) in thalamus. To find corresponding evidence in rats, an Alexa Fluor-conjugated cholera toxin subunit B (CTB) retrograde tracer and an E-YFP anterograde viral tracer were injected into FOF and SC respectively to examine possible overlapping projections in MD. Overlapping projections were found in MD and in surrounding areas. The boundaries of the overlapping projections were defined at AP -1.72 mm to AP -3.84 mm. With a more precise outlining of the intermediate connection in MD, it would be possible to conduct inhibition studies in rats to understand the role this ascending pathway plays in evidence accumulation and decision making.