Non-invasive brain imaging experiments (e.g., fMRI, EEG, or MEG) provide a good starting point for investigating large scale brain responses associated with changes in subjective feeling; but, these technologies lack the necessary spatial and temporal resolution and the chemical specificity to understand the computational processes that drive human behavior and associated subjective experiences. My team recently developed new technology that allows, for the first time ever, high temporal resolution (i.e., sub-second) measurements of the neurotransmitters dopamine and serotonin from deep within the human brain during sequences of conscious actions with reinforcing feedback. We paired this technology with tasks designed to test hypotheses about the role dopamine and serotonin play during adaptive decision-making. We discovered that sub-second fluctuations in dopamine and serotonin encoded learning signals that guide human behavior and are consistent with signals that could influence subjective experience. Specifically, both dopamine and serotonin fluctuations appeared to parametrically encode reward prediction errors about actual and counterfactual outcomes; the latter being consistent with psychological constructs of regret or relief. Here we discuss our current efforts to use our unique intracranial research platform to investigate possible connections between sub-second fluctuations in dopamine and serotonin release and moment-to-moment changes in subjective feelings in humans.