The interhemispheric transfer of visual stimuli and its relation to functional cerebral asymmetries

Sogar ganz einfache und alltägliche Tätigkeiten wie lesen, laufen oder sich die Schnürsenkel zubinden erfordern einen Informationsaustausch zwischen den beiden Gehirnhälften. Wie dieser Austausch funktioniert, ist bislang jedoch nahezu unverstanden. Die vorliegende Arbeit untersuchte ihn deshalb mit mehreren Versuchsparadigmen. Es zeigte sich, dass er wesentlich begrenzter ist als bislang angenommen: wenn beide Gehirnhälften Stimuli verarbeiten, ist ihre Kommunikation stark reduziert und auch nach mehreren Stunden verbleiben signifikante Informationslücken zwischen stimulierter und naiver Gehirnhälfte. Die Daten zeigten jedoch auch, dass der Austausch wesentlich flexibler ist als bislang gedacht: er variiert je nach Stimulusmerkmal und Aufgabe. Außerdem zeigte sich, dass die Kommunikation stark durch die Spezialisierungen der beiden Gehirnhälften geprägt ist: wenn sich die kognitiven Verarbeitungsstile der Gehirnhälften sehr unterscheiden, ist ihre Interaktion nicht immer vorteilhaft.Even simple everyday life activities such as walking or tying ones shoelaces require that the two brain hemispheres communicate with each other. Up to now, however, it is largely unknown how this communication works. Hence, this thesis investigated the exchange with a number of paradigms. It turned out that it is much more restricted than previously assumed: it is mitigated when both hemispheres process stimuli and it is even after several hours only very fragmentary, so that there remain stable knowledge gaps between informed and naive hemisphere. It turned out as well, however, that the exchange is much more flexible than previously thought: it decreases and increases with current task demands and it varies for particular stimulus features. Finally, it was found that the crosstalk is closely related to hemispheric differences: when the cognitive processing styles of the hemispheres differ, the benefit of the transfer depends strongly on its direction

Social reward improves the voluntary control over localized brain activity in fMRI-based neurofeedback training

Neurofeedback (NF) based on real-time functional magnetic resonance imaging (rt-fMRI) allows voluntary regulation of the activity in a selected brain region. For the training of this regulation, a well-designed feedback system is required. Social reward may serve as an effective incentive in NF paradigms, but its efficiency has not yet been tested. Therefore, we developed a social reward NF paradigm and assessed it in comparison with a typical visual NF paradigm (moving bar). We trained twenty-four healthy participants, on three consecutive days, to control activation in dorsal anterior cingulate cortex (ACC) with fMRI-based NF. In the social feedback group, an avatar gradually smiled when ACC activity increased, whereas in the standard feedback group, a moving bar indicated the activation level. In order to assess a transfer of the NF training both groups were asked to up-regulate their brain activity without receiving feedback immediately before and after the NF training (pre- and post-test). Finally, the effect of the acquired NF training on ACC function was evaluated in a cognitive interference task (Simon task) during the pre- and post-test. Social reward led to stronger activity in the ACC and reward-related areas during the NF training when compared to standard feedback. After the training, both groups were able to regulate ACC without receiving feedback, with a trend for stronger responses in the social feedback group. Moreover, despite a lack of behavioral differences, significant higher ACC activations emerged in the cognitive interference task, reflecting a stronger generalization of the NF training on cognitive interference processing after social feedback. Social reward can increase self-regulation in fMRI-based NF and strengthen its effects on neural processing in related tasks, such as cognitive interference. A particular advantage of social feedback is that a direct external reward is provided as in natural social interactions, opening perspectives for implicit learning paradigms