Neuropsychology

Dual-task (DT) situations require task-order coordination processes that schedule the processing of two temporally overlapping tasks. Evidence for these processes stems from the observation that when participants can freely decide about task order they tend to repeat the task order of the previous trial resulting in fewer order switches compared to order repetitions. This order repetition bias suggests that intentionally switching compared to repeating task order requires additional and intention-based task-order coordination processes. In two experiments, we investigated whether the dorsolateral prefrontal cortex (dLPFC) is causally involved in implementing these intentional scheduling processes by employing transcranial direct-current stimulation (tDCS). For this purpose, we applied a DT consisting of an auditory and a visual 3-choice reaction time task with random stimulus order. Importantly, participants were instructed to freely decide about task order. Additionally, in a control condition, participants were instructed to perform the two tasks with constant (and not changing) task order. Anodal (Experiment 1) and cathodal (Experiment 2) tDCS was administered over the left dLPFC. As a result, anodal stimulation improved whereas cathodal stimulation impaired DT performance in order switch trials compared to sham stimulation. Performance in order repetition trials as well as in the control condition was unaffected by stimulation. In sum, our experiments indicate that the dLPFC is indeed causally involved in intentionally switching task order and, thus, contributes to self-organized task scheduling in multitasking situations.

To examine practice related changes in valence-dependent neural feedback processing, thirty-two students learned a sequential arm movement with 192 trials in each of five practice sessions. EEG was recorded in the first and last session. An adaptive bandwidth for movement accuracy led to equal amounts of positive and negative feedback. The ‘feedback-related-negativity’ (FRN; 250 ms after feedback onset) reflects reward prediction errors in reinforcement learning (Holroyd & Coles, 2002). In this study, a frontal located deflection in the time window of the FRN was more negative for negative feedback (p>.001; η2p=.41). An increase of this negativity after the practice phase (p=.002; η2p=.26), indicates that the smaller errors in the later practice might be harder to predict. The P300 (300 ms after feedback onset) is associated with updating of internal models (Donchin & Coles, 1988). Here, the P300 was more positive for positive feedback (p>.001; η2p=.35), yielding that positive feedback is more effective for updating processes. The valence-independent increase (p=.017; η2p=.17) after the practice phase might reflect an improved ability to update the internal model, based on feedback information. The late fronto-central positivity (LFCP; 450 ms after feedback onset) reflects processes of supervised learning (Krause, Koers & Maurer, in press). As expected, the LFCP was more positive for negative feedback (p>.001; η2p=.32) and is assumed to be associated with behavioral adaptions based on feedback with higher complexity. Together, these results demonstrate changes in valence-dependent neural feedback processing after practice of a motor task.

To date, the extent to which neural activity related to romantic love is affected by couple conflict is unknown. Furthermore, there is still a scarcity of studies on interventions that can promote conflict resolution in romantic couples. To fill these gaps, we conducted two randomized controlled studies (Study 1 N = 74; Study 2 N = 72). In both studies, romantic couples discussed a topic of recurrent disagreement with or without a mediator. Romantic couples in the mediated condition reported more agreements and higher satisfaction compared to the non-mediated condition. Functional magnetic resonance imaging data show that seeing the romantic partner was related to activations in striatum, insula, and precuneus prior to the conflict. However, these activations decreased after the conflict. Nonetheless, couples in the mediated condition had higher post-conflict activations the nucleus accumbens – a key region for reward – than couples in the non-mediated condition.

The Rotation-Related-Negativity (RRN), an ERP component emerging 300-600 ms after stimulus onset at parietal electrodes (Provost et al., 2013), increases with higher requirements of mental rotation. In the experiment, stimulus sets of human figures (backview; left/ right arm abduction) and alphanumeric characters („R“; normal/ mirrored) were used. Participants (n = 26; 21.77 years, SD = 1.95) had to judge parity between an upright (0°-orientation) and a comparison stimulus (stimulus disparity; 0°, 45°, 90°, 135° or 180°). There was a significant main effect of orientation for the behavioral (reaction time), F = 72.69, p < .001, eta²p = .74, as well as for the neural data (RRN), F = 32.97, p < .001, eta²p = .57. The interaction with stimulus type was not significant for the reaction time, F = 0.67, p = .511, eta²p = .03, but for the RRN, F = 3.26, p = .031, eta²p = .12. Lower RRN-amplitudes for parity-judgment of letters indicate a more pronounced use of alternative processes (e.g., memory retrieval) other than mental rotation to identify letters as being normal or mirrored. Future studies might clarify if the assumed differential use of memory retrieval also explains that the correlation between RRN-amplitude and the slope of the reaction time as a function of disparity is only evident for the stimulus set of letters, but not for bodies.

In order to better understand stress responses, neuroimaging studies have investigated the underlying neural correlates of stress. Amongst other brain regions, they highlight the involvement of the prefrontal cortex. Here we investigate haemodynamic changes in the prefrontal cortex during the Maastricht Acute Stress Test (MAST) using mobile functional Near-Infrared Spectroscopy (fNIRS), examining the stress response in an ecological environment. The MAST includes a challenging mental arithmic task and a physically stressful ice-water task. In a between-subject design, participants either performed the MAST or a non-stress control condition. FNIRS data were recorded throughout the task. Additionally, subjective stress ratings, heart rate and salivary cortisol were evaluated, confirming a successful stress induction. The fNIRS data indicated significantly increased neural activity of brain regions of the dorsolateral prefrontal cortex (dlPFC) and the orbitofrontal cortex (OFC) in response to the MAST, compared to the control condition. Furthermore, the mental arithmetic task indicated an increase in neural activity in brain regions of the dlPFC and OFC; whereas the physically stressful hand immersion task indicated a lateral decrease of neural activity in the left dlPFC. The study highlights the potential use of mobile fNIRS in clinical and applied stress research.