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Thesis Format



Master of Science




Martinez-Trujillo, Julio C.


The hippocampus is a neural structure critical for navigation. Neurons in this region, along with others, create a functional network which generates large-amplitude modulations known as local field potential (LFP) activity. Prior LFP research has predominantly used rodent animal models, however recent studies have shown that frequencies associated with navigation in other mammals do not correlate to those of the rodent. We hypothesized that LFP characteristics in the common marmoset are modulated by the speed and axis of travel of the animal. Two marmosets were placed in a free moving 3-dimensional environment where movement and neurological activity were recorded. Results showed LFP modulation based on movement, including significant changes in power with movement speed and vertical motion. We provide evidence of theta bout activity and other non-rodent-like characteristics, prompting discussion on the generalization of findings in rodent models such as mice and rats to primate navigation.

Summary for Lay Audience

The region of the brain in mammals responsible for navigation is found in the medial temporal lobe, known as the hippocampus. Neurons in the hippocampus produce brain waves called local field potentials (LFP). These LFPs can be broken down into the different frequency oscillations and their relative contribution (power), allowing the analysis of specific frequency bands. These LFPs are thought to be linked to neural function as they are a product of populations of neurons synchronously firing and are predominantly correlated to certain behaviors. The vast majority of prior LFP research has been conducted using rodent animal models such as rats and mice, but recent studies have shown that LFPs associated with navigation in other mammals (bats, monkeys, humans) do not show the same features as the rodent’s LFPs. Here, we looked to analyze the modulation of LFP profiles in the common marmoset in a freely moving 3-dimensional environment. The animals had the ability to freely move in a plexiglass enclosure while their movement and neural activity recorded was in real time. Taking this data, we divided movement into five categories: stationary, horizontal-slow, horizontal-fast, vertical-up, and vertical-down. We hypothesized that the marmoset’s speed and direction of motion influence features of hippocampal LFPs. Our results show that LFP profiles change based on movement speed and direction of travel, stationary and vertical movement being on opposite ends of the spectrum in regard to LFP frequency power. We also provide evidence that marmosets have similar LFP profiles as other primates in the theta frequency band associated with navigation, which is not modulated by the speed of movement while in motion. These findings provide further evidence of non-rodent-like characteristics exhibited in marmosets, prompting discussion on the generalization of findings in rodent models, such as mice and rats, to primate navigation.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.