Sprengel, Michael

Research investigating the effects of carbohydrate (CHO) mouth rinsing on neurocognitive functions is currently limited and has yielded inconsistent results. In this study, we employed the event-related potential (ERP) electroencephalography technique to investigate the effect of CHO mouth rinsing on electrophysiological correlates of visuospatial attention. Using a double-blind, non-nutritive sweetener (NNS)-controlled, within-subjects design, 53 young adults performed a standard cognitive task (modified Simon task) on two separate days in a fasted state (16 h). Intermittently, mouth rinsing was performed either with a CHO (glucose, 18%, 30 mL) or an NNS solution (aspartame, 0.05%, 30 mL). Results revealed that relative to NNS, electrophysiological correlates of both more bottom-up controlled visuospatial attention (N1pc-ERP component) were decreased in response to CHO rinsing. In contrast, compared to NNS, more top-down controlled visuospatial attention (N2pc-ERP component) was increased after CHO rinsing. Behavioral performance, however, was not affected by mouth rinsing. Our findings suggest that orosensory signals can impact neurocognitive processes of visuospatial attention in a fasted state. This may suggest a central mechanism underlying the ergogenic effects of carbohydrate mouth rinsing on endurance performance could involve modulations of attentional factors. Methodologically, our study underlines that understanding the effects of carbohydrate mouth rinsing at the central level may require combining neuroscientific methods and manipulations of nutritional states.

The list-level proportion congruency effect (PCE) and the context-specific PC (CSPC) effect are typical findings in experimental conflict protocols, which competing explanations attribute to different mechanisms. Of these mechanisms, stimulus-unspecific conflict-induced selectivity adjustments have attracted the most interest, from various disciplines. Recent methodological advances have yielded an experimental procedure for entirely ruling out all stimulus-specific alternatives. However, there is a stimulus-unspecific alternative–temporal learning–which cannot even be ruled out as the sole cause of either effect with any established experimental procedure. That is because it is very difficult to create a scenario in which selectivity adjustments and temporal learning make different predictions–with traditional approaches, it is arguably impossible. Here, we take a step towards solving this problem, and experimentally dissociating the two mechanisms. First, we present our novel approach which is a combination of abstract experimental conditions and theoretical assumptions. As we illustrate with two computational models, given this particular combination, the two mechanisms predict opposite modulations of an as yet unexplored hybrid form of the list-level PCE and the CSPC effect, which we term context-dependent PCE (CDPCE). With experimental designs that implement the abstract conditions properly, it is therefore possible to rule out temporal learning as the sole cause of stimulus-unspecific adaptations to PC, and to unequivocally attribute the latter, at least partially, to selectivity adjustments. Secondly, we evaluate methodological and theoretical aspects of the presented approach. Finally, we report two experiments, that illustrate both the promise of and a potential challenge to this approach.

The congruency sequence effect (CSE) and the proportion congruency effect (PCE) are typical findings in experimental conflict protocols. Given the ever-increasing number of, in part, radically different mechanisms proposed to explain either effect, a unified system for describing candidate mechanisms appears desirable. In this article, we show that such a system can be derived by focusing on functional similarities among all mechanisms capable of explaining either effect. The latter perspective reveals the adaptive dynamic that all such mechanisms share. This shared dynamic allows describing each mechanism by addressing the same questions about how this dynamic is implemented. We contend that this description system facilitates comparisons between mechanisms, and relating the discourse on the CSE and PCE to other lines of discourse. First, we introduce the adaptive dynamic and the questions about its implementation. Then, we answer these questions for exemplary cases. Finally, we discuss the utility of the proposed system.

Human research has shown interactions between rewards and cognitive control. In animal models of affective neuroscience, reward administration typically involves administering orosensory sugar signals (OSS) during caloric-deprived states. We adopted this procedure to investigate neurophysiological mechanisms of reward-cognitive control interactions in humans. We predicted that OSS would affect neurophysiological and behavioral indices of error processing oppositely, depending on the relative weight of the OSS-induced ‘wanting’ and ‘liking’ components of reward. We, therefore, conducted a double-blind, non-nutritive sweetener-controlled study with a within-subject design. Fasted (16 hr) participants (N = 61) performed a modified Flanker task to assess neurophysiological (error-related negativity [Ne/ERN]) and behavioral (post-error adaptations) measures of error processing. Non-contingent to task performance, we repeatedly administered either a sugar (glucose) or non-nutritive sweetener (aspartame) solution, which had to be expulsed after short oral stimulation to prevent post-oral effects. Consistent with our hypothesis on how ‘liking’ would affect Ne/ERN amplitude, we found the latter to be decreased for sugar compared to aspartame. Unexpectedly, we found post-error accuracy, instead of post-error slowing, to be reduced by sugar relative to aspartame. Our findings suggest that OSS may interact with error processing through the ‘liking’ component of rewards. Adopting our reward-induction procedure (i.e. administering OSS in a state of high reward sensitivity [i.e. fasting], non-contingent to task performance) might help future research investigating the neural underpinnings of reward-cognitive control interactions in humans.

The Congruency Sequence Effect (CSE) denotes the common finding that distractor–target Congruency Effects are reduced after incongruent compared to after congruent trials. Although the CSE is widely attributed to attentional adjustment (i.e., increasing or decreasing the bias in attentional weights regarding processing the target or distractor), unequivocal evidence for this assumption is missing. To investigate the CSE and attentional adjustment we used a temporal flanker task and intermixed a “temporal search task”, in which a target stimulus occurred randomly at one of two temporal positions, corresponding to the temporal positions of the target and the distractor occurrence in the temporal flanker task. We observed a CSE that could not be explained in terms of feature sequences, distractor-related contingencies, or a strategy of reversed distractor–response priming after incongruent trials. Furthermore, following a temporal search task trial, the Congruency Effect was larger when the search target occurred on the first than on the second temporal position, demonstrating that a reduced attentional bias towards the second temporal position increased interference from a distractor presented on the first temporal position. This supports a crucial assumption of the attentional adjustment account of the CSE. Performance in the temporal search task, however, provided no evidence for attentional adjustment. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.