Ständig kontrollieren wir das Ergebnis unserer Handlungen. Ist das Ergebnis ein anderes als erwartet, wird dies als Fehler erkannt und es erfolgt dann der Versuch, das Verhalten entsprechend anzupassen. Die zugrunde liegenden elektrophysiologischen Korrelate können mittels Ereignis-korrelierter Potentiale untersucht werden (ERN, „error-related negativity“ und Pe, „error positivity“). Offenkundige und latente Dysfunktionen der Handlungsüberwachung, die unter anderem durch pathologische Veränderungen der kortikalen Exzitabilität bedingt werden, konnten bei Patienten mit neurologischen und psychiatrischen Erkrankungen beobachtet werden. Die Modulation der für die Fehlerverarbeitung relevanten Hirnregionen des medialen präfrontalen Kortex wäre deshalb wünschenswert und soll in der vorliegenden Arbeit untersucht werden. Eine Möglichkeit zur Modulation zerebraler Erregbarkeit stellt die Transkranielle Gleichstromstimulation (tDCS) dar. In unserer Untersuchung haben wir den Effekt von tDCS bei 48 gesunden Teilnehmern getestet, die drei Gruppen randomisiert zugeordnet wurden (anodale, kathodale und SHAM-Stimulation). Während einer 22-minütigen Stimulation mit tDCS über dem medialen frontalen Kortex führten die Probanden eine modifizierte Eriksen Flanker Aufgabe aus. Parallel dazu wurde ein EEG zur Analysierung der ERN und Pe aufgenommen. Es konnte gezeigt werden, dass kathodale Stimulation im Vergleich zu anodaler und SHAM Stimulation die Amplitude von Subkomponenten der Pe verringert, während kein Effekt auf die ERN nachgewiesen werden konnte. Bei der Untersuchung der Modulation der Fehlerverarbeitung durch transkranielle Stimulation mit tDCS konnten wir somit Hinweise auf einen kathodal-inhibitorischen Effekt auf die kortikale Exzitabilität bei gesunden Probanden finden, was Perspektiven für eine zukünftige Modulation der zugrunde liegenden neuronalen Netzwerke eröffnet. Trotzdem werden weitere Studien notwendig sein, um zu klären, inwieweit der Effekt auf die späte Pe auch von funktioneller Relevanz ist. Zukünftige Studien werden die (Patho)physiologie zugrunde liegender Fehlerüberwachungssysteme auf Zell- und Systemebene weiter untersuchen müssen, um eine Optimierung der stimulations-induzierten Effekte erreichen zu können und um tDCS als eine mögliche wertvolle Therapieoption für Patienten mit Dysfunktionen der Fehlerverarbeitung etablieren zu können. / Background: In order to prevent future errors, we constantly control the outcome of our actions to detect a discrepancy between the expected (i.e., intended) outcome and the real outcome, and continuously adjust our behavior accordingly. The underlying neurophysiological correlates of error monitoring can be studied with event-related potentials (the error-related negativity (ERN) and error positivity (Pe), Falkenstein et al., 2001). Patients with neurological and psychiatric diseases show overt and latent performance monitoring dysfunctions that can (amongst others) be caused by pathological changes of cortical excitability, therefore a modulation of the underlying neuronal activity might be a valuable therapeutic tool. One technique which allows us to explore cortical modulation of neural networks is transcranial direct current stimulation (tDCS). Hence, with our study we intended to analyse, whether tDCS can be used to modify error monitoring systems by altering the underlying neuronal activity. Therefore, we tested the effect of tDCS on 48 healthy subjects randomly assigned to three groups, anodal, cathodal or sham stimulation. The subjects underwent tDCS over the medial frontal cortex while performing an Erisken flanker task during a simultaneous EEG recording, allowing for an analysis of the ERN and Pe. Results: We found that cathodal stimulation attenuated Pe amplitudes compared to anodal stimulation and to SHAM stimulation, but no effect for the ERN. Conclusions: Based on these findings, modulation of the medial frontal cortex with weak direct current can be seen as a future approach to modify the sensitivity of the error monitoring system, and should be tested in future studies with psychiatric patients with performance monitoring dysfunctions.

No description available.

The cerebral cortex contains many neurons. The neuron is part of the nervous system and it receives and transmits the electrical signals. These signals are significant to a human's behaviour. Since the neurons are charged, these charges produce electrical fields, so these neural signals can be measured by using scalp electrodes in electroencephalography (EEG). As long as the brain is not dead, the spontaneous activities of neurons will produce a series of EEG signals. There are many models that have been developed for simulating the cortical signal, and mostly each model is focused towards a different purpose or application. Often, a different computer code has to be written for each different application, and this can be inefficient. Therefore, this project aims to develop a software system for simulating cortical signals where the model used for the system can be changed easily. Furthermore, the system is requested to be versatile and easy-to-use for many applications. The developed system is written in MATLAB in response to a user requirement and mostly applies to any model which uses a mean-field approach. Only the specific inputs need to be modified for changing the model. This thesis details how this system is developed. The main limitation of the system is computational resources, much the same as other cortical modelling. However, all the user requirements had been satisfied. The system can simulate the response of the neurons for any condition and generate simulated EEG data to the user. The user can analyze the cortical activities using the standard signal processing techniques such as a power spectrum. This software is very helpful for the research of sleep and anaesthesia.

This thesis examines the dynamical behaviour of incorporating NMDA (an excitatory neurotransmitter) for the electrodynamic model of the cerebral cortex. The model used is the mean-field model developed by Steyn-Ross et al. (2005) which describes the behaviour of the cortex in terms of parameters averaged over spatially localised populations. The behaviour of the model is determined by the four control parameters: inhibitory effect li, subcortical drive s, and NMDA neurotransmitter e ect set by an excitatory factor le and the magnesium concentration C. Adopting this model could give a better understanding of the cortex functionality and the anaesthetic mechanism. The model predicts that there are either one or three stationary states available to the cortex. We identify two of these with highly activated state and a quiescent state and focus on the transition between the two. Theoretical stability predictions (eigenvalue analysis) verified by a numerical simulation show that the system is unstable between the two Hopf bifurcations. In addition, in the stable region the steady states remains stable under a small perturbation, while in the unstable region either a transition between states or a limit cycle (oscillation) occurs depending on the position of the steady state.

Anatomical connectivity and single neuron coding suggest a dissociation of information representation within the lateral and medial entorhinal cortex, a brain region with widespread connections to cortical areas. We aimed to expand this idea by examining differential contribution of these two sub-regions to the retrieval of non-spatial and spatial memory. Inactivation of lateral, but not medial regions severely impaired the retrieval of recently and remotely acquired non-spatial memory while spatial memory remained intact. To link functioning of the lateral entorhinal cortex with the known roles of the hippocampus and medial prefrontal cortex for memory retrieval, communication with these two regions was detected as synchronized oscillations in local field potentials. We found that stronger communication between the lateral entorhinal and prefrontal cortex during stimulus-free periods correlated with better memory performance. The lateral entorhinal cortex therefore may serve as a gateway of memory-related information between the medial prefrontal and other cortical regions.

Anatomical connectivity and single neuron coding suggest a dissociation of information representation within the lateral and medial entorhinal cortex, a brain region with widespread connections to cortical areas. We aimed to expand this idea by examining differential contribution of these two sub-regions to the retrieval of non-spatial and spatial memory. Inactivation of lateral, but not medial regions severely impaired the retrieval of recently and remotely acquired non-spatial memory while spatial memory remained intact. To link functioning of the lateral entorhinal cortex with the known roles of the hippocampus and medial prefrontal cortex for memory retrieval, communication with these two regions was detected as synchronized oscillations in local field potentials. We found that stronger communication between the lateral entorhinal and prefrontal cortex during stimulus-free periods correlated with better memory performance. The lateral entorhinal cortex therefore may serve as a gateway of memory-related information between the medial prefrontal and other cortical regions.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 129-138).

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Figure 1 referred to on leaf 2 is shown on leaf 20. Typescript. Includes bibliographical references (leaves 35-36). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Figure 1 referred to on leaf 2 is shown on leaf 20. Typescript. Includes bibliographical references (leaves 35-36). Also available on the Internet.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xiii, 184 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Andrej Rotter, Dept. of Biochemistry. Includes bibliographical references (p. 158-184).