Project 461896

Spatial navigation involves the formation of cognitive maps of the environment containing spatial relationships between objects. Past studies have shown that the mammalian brain possesses an instantiation of such cognitive map in structures such as the hippocampus. In the rodent hippocampus, studies have identified place cells, head direction cells, time cells and speed cells that allow for the encoding of the position of an animal in the cognitive map and self-orienting during navigation. Studies have also reported the existence of hippocampal theta oscillations, thought to be essential for cognitive map formation. However, studies in primates such as macaque monkeys have reported other cell types such as view cells, and a decrease in the rhythmicity and power of the hippocampal theta oscillations compared to rodents. It is likely that the primate hippocampus underwent changes during evolution due to the expansion of neocortical areas associated to vision. A challenge to studies of spatial navigation in primates is developing a model that allows for single cell level exploration and interrogation of hippocampal circuits. Most studies in primates are conducted in head-restrained animals, using computer displays and virtual navigation via joysticks, differing from studies in freely moving rodents that allow full recruitment of sensory and motor structures involved in navigation. Therefore, it has been difficult to identify the elements of the hippocampal system that have been preserved through mammalian evolution and those that emerged in primates. In this proposal we will first develop a non-human primate model of spatial navigation, the freely moving marmoset, for single cell exploration and interrogation of hippocampal circuits. Second, we will test the hypothesis that some elements of the hippocampus cognitive map are preserved from rodents to primates, but primates have evolved new elements for adapting to their ecological niches.