How surprise and uncertainty alter brain state and decisions

Our natural environment can be characterized as a complex combination of statistical regularities and change. Nonetheless, humans and other species are generally successful decision makers. To achieve this, we need to be able to transform prior experience into expectations to guide our actions, while at the same time judge the validity of these history-based expectations in the current environment. This dissertation reports a combination of decision-making tasks and methods to gain insight into the central question: how do surprise and uncertainty alter brain state and decisions? The degree to which our expectations should shape our decisions depends on the level of uncertainty we have about them. Surprise serves as a warning signal that the expectations might not be valid.
Uncertainty about choice outcome makes decisions more variable through upregulation of noise in the transformation of history-based expectations into the current and subsequent choices. Pharmacological upregulation of catecholamines caused the same effect, suggesting that uncertainty affects decision-making by activation of neuromodulatory brainstem nuclei. Surprise, caused by either temporally surprizing stimulus changes or unexpected outcomes of foraging choices, caused transient neurophysiological modulations, which likely reflect the monitoring process that updates expectations by the feedback from the environment.
This dissertation contributes to the understanding of decision-making in real-life environments. Expectations are formed and updated based on feedback from the environment. Expectations affect decisions depending on the level of uncertainty we have about the environment. Uncertainty makes decisions more random, and thereby provides a mechanism to be flexible to changes in the environment.