Dissertation Defense: Decision-making Under Uncertainty: Neural Hard-wiring of Behavioral Algorithms
Dissertation Defense
Decision-making Under Uncertainty: Neural Hard-wiring of Behavioral Algorithms
Natalie Melville
Graduate Student, Translational Biology, Medicine, and Health
Graduate Research Assistant, Casas Lab, Fralin Biomedical Research Institute at VTC
May 5, at 9 a.m.
Virtual Option Only
About this Dissertation
Every day humans make decisions under uncertainty where there are multiple potential outcomes. To do this, multiple pieces of information are integrated: potential outcomes and the likelihoods of those outcomes. In some cases, the likelihoods of each outcome are known, known as risks, and in other cases the likelihoods of each outcome are unknown, known as ambiguity. While most individuals have aversion towards both types of uncertainty, risks and ambiguity, the strength of that aversion changes across individuals. Specifically, adolescents’ aversion towards ambiguity decreases while aversion towards risk is the same as adults. In the frontoparietal network (FPN), decreased risk-aversion is associated with increased activity in the right frontal node and increased ambiguity-aversion is associated with increased activity in the left parietal node. Meanwhile, the insula, dorsomedial prefrontal cortex (dmPFC), and the thalamus are consistently activated. This dissertation elucidates upon the decision-making process by looking at the integrated effects of ambiguity and risk on choice behavior (Study 1 and 2), a proposed algorithm for integrating likelihood information (Study 1 and 2), and the neural hardwiring of decisions under varying types of uncertainty (Study 2 and 3). Study 1 looks at this in adults, Study 2 in adolescents, and Study 3 in an older adult population. favorability of the risk information resulted in greater pessimism towards ambiguity particularly in adults and mid-adolescents. Increased perceived favorability of ambiguous likelihoods was associated with increased dmPFC and insula activity. The thalamus, functionally connected to the dmPFC and insula, had increases in dopamine (DA), decreases in norepinephrine (NE) in response to increased uncertainty. The summation of both DA nor NE was most associated with model-derived choice. Decision-making under uncertainty involves integration of information. Behaviorally, the integration of both risk and ambiguity information affects choice. In the neural hardwiring, both DA and NE affected choice. These results elucidate on the mechanics behind decisions under uncertainty and create important hypothesis to be further tested in larger populations.
More About the Candidate and Project
Education
Virginia Tech, Translational Biology, Medicine, and Health, Ph.D. Candidate
Tulane University, B.S., Physics
Tulane University, B.A., Economics
Training
Graduate Research Assistant, Casas Lab, Fralin Biomedical Research Institute at VTC
Mentors
Brooks Casas, Ph.D., Professor, Fralin Biomedical Research Institute at VTC; College of Science Faculty Fellow, Virginia Tech
Committee Members
- Pearl Chiu, Ph.D., Professor, Fralin Biomedical Research Institute at VTC; Patricia Caldwell Faculty Fellow, Virginia Tech
- Read Montague, Ph.D., Virginia Tech Carilion Vernon Mountcastle Research Professor, Fralin Biomedical Research Institute at VTC; Director, Center for Human Neuroscience Research, Virginia Tech
- Mark R. Witcher, M.D., Ph.D., Functional Neurosurgery, Carilion Clinic; Vice Chair for Research and Education, Department of Neurosurgery, Virginia Tech Carilion School of Medicine
Publications
Melville, N., Li, F., Wang, S., Ball, S., Chiu, P., Casas, B. (Submitted for Publication). Ambiguity preferences are made up of two distinct linear biases: optimism and known likelihood sensitivity. Journal of Neuroscience, Psychology, and Economics.
Melville, N., Li, F., Ball, S., Kim-Spoon, J., Chiu, P., Casas, B. (In Preparation). Known Probability Information Influence Development of Decision-Making under Uncertainty in Adolescents.
Lindenmuth, M., Chen, Y. Y., Lee, T. H., Melville, N., Casas, B., & Kim-Spoon, J. (2025). A six-year longitudinal study examining chronicity and timing of maltreatment effects on risk-related functional connectivity change across adolescence. Developmental cognitive neuroscience, 74, 101577. https://doi.org/10.1016/j.dcn.2025.101577
Melville, N., Ball, S., Batten, S., Kim, D.Y., Jarrett, C., Venkatesh, J., Barbosa, L., Twomey, T., White, J., Lohrenz, R., Witcher, M., Montague, P.R., Chiu, P., Casas, B. (In Preparation). Risk seeking individuals have anticorrelated dopamine and norepinephrine during decision-making under risk.
Batten, S. R., Hartle, A. E., Barbosa, L. S., Hadj-Amar, B., Bang, D., Melville, N., Twomey, T., White, J. P., Torres, A., Celaya, X., McClure, S. M., Brewer, G. A., Lohrenz, T., Kishida, K. T., Bina, R. W., Witcher, M. R., Vannucci, M., Casas, B., Chiu, P., Montague, P. R., … Howe, W. M. (2025). Emotional words evoke region- and valence-specific patterns of concurrent neuromodulator release in human thalamus and cortex. Cell reports, 44(1), 115162. https://doi.org/10.1016/j.celrep.2024.115162
Bang, D., Luo, Y., Barbosa, L. S., Batten, S. R., Hadj-Amar, B., Twomey, T., Melville, N., White, J. P., Torres, A., Celaya, X., Ramaiah, P., McClure, S. M., Brewer, G. A., Bina, R. W., Lohrenz, T., Casas, B., Chiu, P. H., Vannucci, M., Kishida, K. T., Witcher, M. R., … Montague, P. R. (2023). Noradrenaline tracks emotional modulation of attention in human amygdala. Current biology : CB, 33(22), 5003–5010.e6. https://doi.org/10.1016/j.cub.2023.09.074
Presentations
Melville N, Li F, Ball S, Kim-Spoon J, Chiu P, Casas B. Known and unknown probability information separably modulate insula activity in adolescents. Organization for Human Brain Mapping. 2024. Seoul, South Korea. Abstract
Melville N, Li F, Ball S, Kim-Spoon J, Chiu P, King-Casas B. Known Probability Information Influences How Adolescents Respond to Ambiguity. Fralin Biomedical Research Institute Annual Retreat. 2023. Hot Springs, VA. Poster
Melville N, Lohrenz T, White J, Barbosa L, Twomey T, Batten S, Ball S, Sands P, Levy I, Torres A, Celaya X, Ramaiah P, Bina R, Witcher M, Brewer G, McClure S, Montague P R, Chiu P, Casas B. Dopamine and Norepinephrine in Amygdala During Risky Choice. Interdisciplinary Symposium on Decision Neuroscience. 2023. Philadelphia, PA. Poster and Oral Presentation
Melville N, Lohrenz T, White J, Barbosa L, Twomey T, Batten S, Ball S, Sands P, Levy I, Torres A, Celaya X, Ramaiah P, Bina R, Witcher M, Brewer G, McClure S, Montague P R, Chiu P, Casas B. Dopamine and Norepinephrine in Amygdala During Risky Choice. Translational Biology, Medicine & Health Symposium. 2023. Roanoke, VA. Poster
Melville N, Li F, Ball S, Kim-Spoon J, Chiu P, King-Casas B. Known Probability Information Influences How Adolescents Respond to Ambiguity. Society for Neuroeconomics. 2022. Arlington, VA. Poster
Melville N, King-Casas B, Chiu P. Dopamine and Norepinephrine Opponency during Reward Anticipation. Fralin Biomedical Research Institute Annual Retreat. 2022. Hot Springs, VA. Poster
Melville N, King-Casas B, Chiu P. Dopamine and Norepinephrine Opponency during Reward Anticipation. Society of Biological Psychiatry. 2022. New Orleans, LA. Poster
Melville N, Li F, Ball S, Kim-Spoon J, Chiu P, King-Casas B. Known Probability Information Influences How Adolescents Respond to Ambiguity. Translational Biology, Medicine & Health Symposium. 2022. Roanoke, VA. Poster
Melville N, Li F, Wang S, Ball S, Kim-Spoon J, Chiu P, Casas B. Known Probability Information Influences How Adolescents Respond to Ambiguity. Economics Science Association. 2023. Charlotte, NC. Oral Presentation
Melville N, Chiu P, King-Casas B. Adolescent Risky Decision Making. Virginia Tech Board of Visitors. 2022. Blacksburg, VA. Oral Presentation
Melville N, Waldman A, Schmieley R. Pixellar: Future of vision prosthetics. Translational Biology Medicine & Health Pitch Competition. 2019. Roanoke, VA. Oral Presentation
- Honorable Mention: NSF Graduate Research Fellowship Program. 2021.
- Most Creative: Translational Biology, Medicine & Health Pitch Competition. 2019.
- Education Committee Advisor for inner-city school in Guatemala. 2022-2026
- Brain Awareness Week. Guest lecturer in local high school. 2023
- Human Neuroscience Graduate Student Congress at Virginia Tech. Treasurer. 2021-2023
- Agape Center. Connect local volunteers. 2021-2022