The Study of Rhesus Monkey’s Behavior and Neural Connectivity in Social-Hierarchy: Experimental Modeling and Implementation of Computational Analysis Schemes

Abstract

To identify the critical areas of the primate brain involved in social interaction, we define the closed loop between external behaviors and the internal brain neural network. To examine this question, we had four subject monkeys to watch videos of simulated pairwise interactions among them, organized into a virtual hierarchy. We monitored the viewers’ eye movements and neural activities in the amygdala and its network areas. For data analysis, we used three preprocessing methods. First, we measured the amount of movement in the videos by using the optical flow. It was used for answering the question if the movements in the visual stimulus affect the viewer’s gaze behavior. Second, we enhanced the eye movement data to extract precise timings of saccade and fixation onset. Third, we suggested an image segmentation method and showed its performance for the analyses in the future. In this dissertation, we report four results: (1) Viewing pattern analysis that generated data descriptors from the different viewing patterns for each video and observed the classification performance of them. From this analysis, we judge if the viewer monkey learned enough about the information in the visual stimulus. (2) Gaze pattern analysis that identified two types of meaningful saccades: gaze following and joint attention. Temporal alignment of gaze following and joint attention to the frames of each video showed numerous clusters of significant increases in the frequency of these saccades. These clusters suggest that some videos contain signals that can induce a quasi-automatic redirection of the observer’s attention. (3) Single unit data analysis that answered the scientific question: “do neurons in the amygdala, hippocampus and other areas respond differentially to the same individuals paired with a different social partner?” We found the cells that were tuned to fixated target’s social status and social partner in the video. The results were verified by statistical analysis (one-way ANOVA). These effects indicate that the representation of individuals in third-party observers of social interactions depends on the identity of the other individuals that are present in the video even when not fixated on. (4) Local field potential (LFP) data analysis that answered the same question in the single unit analysis. We suggested LFP preprocessing steps to remove artifacts and noise of the original signal. We found that more sites in the amygdala show the difference in the variance of the event related potential (ERP) amplitude with the social status of the fixated individual. In addition, these ERP amplitude differences in amygdala were pronounced in the pre-saccade and saccade periods but not during fixation. In conclusion, we suggested several preprocessing methods for various types of signals that we used or collected during the experiment. Furthermore, we reported many scientific findings in behavioral (i.e., measuring learning status via viewing pattern and discovering meaningful saccade patterns during third-party observation) and neural analyses (i.e., neurons are tuned to fixated target’s social status and its partner) through engineering and mathematical approaches.