Untersuchung des dopaminergen Einflusses auf visuelle Aufmerksamkeit mittels EEG, fMRI und der Kombination beider Methoden mittels Einzel-trial-basierter Analyse
Final Report Abstract
The accomplished research projects have been focused on the function of the dopaminergic system in the broad context of cognitive control. Specifically, there are two important contexts in which a dopaminergic role has been suggested. On the one hand, it has been suggested that it provides a teaching signal that helps optimize behavior based on the outcome of previous actions. On the other hand, it has been firmly established to play a central role in reinforcement learning and concomitant behavioral and neural energetization in the context of reward processing. However, it has been suggested that it could play a similar role also in the absence of reward. With respect to performance monitoring, we have investigated the role of the dopaminergic system in behavioral adjustments that occur after Stop-trials in a Stop-signal task. Specifically, it is known that subjects slow down their response in Go-trials that follow on Stop-trials, and this adjustment has been suggested to reflect an adaptive mechanism. By using single-trial-based parametric modulators that investigated the relationship between brain activity in Stop-trials and the subsequent behavioral adjustment, we could demonstrate that the activity level in the dopaminergic midbrain during Stop-trials indeed predicted the amount of behavioral slowing on the subsequent Stop-trial. Importantly, mirroring the similar behavioral effects, this effect did not differentiate between successful and unsuccessful Stop-trials, so that the underlying mechanism is probably rather related to the rarity of Stop-trials or the engendered response-conflict and not mere error processing. Either way, the relationship between activity in the dopaminergic system and subsequent behavioral adjustments nicely dovetails with suggestions that assign the dopaminergic system the role of providing a teaching signal that opfimizes behavior overtime. With respect to the recmitment of processing resources, we could indeed show that the dopaminergic system can be recruited in a top-down fashion to meet heightened requirements also in the absence of any direct motivators like reward. This finding is highly relevant concerning the interpretation of the specific role that the dopaminergic system plays during the processing of reward-related and reward-unrelated stimuli. We speculate that the dopaminergic system can either be recruited in a bottom-up fashion (by stimuli whose reward-predictiveness has been learned), or top-down (presumably by prefrontal cortex areas). Thus, the dopaminergic system might provide a common currency that enables energy expenditure, which will not only get activated by reward-predicting stimuli (where this expenditure will likely be "paid back" directly), but can also be recruited when a higher level of processing resources is required despite the absence of reward. Such processes might be particularly valuable, when reward-associations have not been learned yet, or when reward contingencies are particularly uncertain but possibly of high value. Efforts to investigate the relationship between activity in the dopaminergic midbrain, as measured with fMRI, and simultaneously-recorded scalp potentials (EEG) are still ongoing.
Publications
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(2010). Pinning down response inhibition in the brain - Conjunction analyses of the Stop-signal task. Neuroimage 52:1621-1632
Boehler CN, Appelbaum LG, Krebs RM, Hopf JM, Woldorff MG
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(2010). The influence of reward associations on conflict processing inthe Stroop task. Cognition 117:341-347
Krebs RM, Boehler CN, Woldorff MG
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(2011). Substantia nigra activity level predicts trial-totrial adjustments in cognitive control. Journal of Cognitive Neuroscience 23:362-373
Boehler CN, Bunzeck N, Krebs RM, Noesselt T, Schoenfeld MA, Heinze HJ, Munte TF, Woldorff MG, Hopf JM
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(2011). Task-Load-Dependent Activation of Dopaminergic Midbrain Areas in the Absence of Reward. The Journal of Neuroscience 31:4955-4961
Boehler CN, Hopf J-M, Krebs RM, Stoppel CM, Schoenfeld MA, Heinze H-J, Noesselt T
