Abstract
Feedback processing is commonly studied by analyzing the brain’s response to discrete rather than continuous events. Such studies have led to the hypothesis that rapid phasic midbrain dopaminergic activity tracks reward prediction errors (RPEs), the effects of which are measurable at the scalp via electroencephalography (EEG). Although studies using continuous feedback are sparse, recent animal work suggests that moment-to-moment changes in reward are tracked by slowly ramping midbrain dopaminergic activity. Some have argued that these ramping signals index state values rather than RPEs. Our goal here was to develop an EEG measure of continuous feedback processing in humans, then test whether its behaviour could be accounted for by the RPE hypothesis. Participants completed a stimulus-response learning task in which a continuous reward cue gradually increased or decreased over time. A regression-based unmixing approach revealed EEG activity with a topography and timecourse consistent with the stimulus-preceding negativity (SPN), a scalp potential previously linked to reward anticipation and tonic dopamine release. Importantly, this reward-related activity depended on outcome expectancy: as predicted by the RPE hypothesis, activity for expected reward cues was reduced compared to unexpected reward cues. These results demonstrate the possibility of using human scalp-recorded potentials to track continuous feedback processing, and test candidate hypotheses of this activity.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Minor revisions to improve clarity. Updated author affiliations.
1 Other names include the feedback-related negativity (FRN), the feedback error-related negativity (fERN), the medial-frontal negativity (MFN), and the feedback negativity (FN). See Proudfit (2015) for a detailed explanation. Also note that there has been debate about whether frontal cortex can be affected directly by dopamine or only indirectly via glutamate (Ullsperger et al., 2014).
2 In general, any anticipated stimulus ought to elicit an SPN. Furthermore, the SPN may be a subcomponent of another ERP component called the contingent negative variation (CNV). See van Boxtel and Böcker (2004) for a discussion.