Der mediale präfrontale Cortex (mPFC) und der anteriore cinguläre Cortex (ACC) sind bei vielen kognitiven Prozessen beteiligt, u.a. bei Aufmerksamkeitsprozessen und Verhaltenskontrolle. Darüber hinaus spielen beide Regionen eine zentrale Rolle bei vielen psychiatrischen Krankheiten. Zwei Paradigmen wurden bisher häufig in elektrophysiologischen Studien eingesetzt, um mediale Frontallappenanteile zu untersuchen: Zum einen das Wahlreaktionsparadigma und zum anderen das Go-/Nogo-Paradigma. In Lokalisationsuntersuchungen mittels Low Resolution Electromagnetic Tomography (LORETA) wurden Aktivierungsmuster im Bereich der frontalen Mittellinie entdeckt. Allerdings ist die räumliche Auflösung elektrophysiologischer Lokalisationsmethoden mit der LORETA limitiert. Diese Einschränkungen hinsichtlich der räumlichen Auflösung existieren nicht für die funktionelle Magnetresonanztomographie (fMRT).

Der anteriore cinguläre Cortex spielt eine bedeutende Rolle für kognitive Funktionen wie Aufmerksamkeits- und Motivationsprozesse. Sein Aktivierungsausmaß ist eng mit der bei einer Wahlreaktionsaufgabe notwendigen mentalen Anstrengung verknüpft. Eine pathologische Funktion des ACC bei psychiatrischen Krankheiten wie der Schizophrenie ist häufig beschrieben worden. Zur Untersuchung der ACC-Funktion wurde in früheren rein elektrophysiologischen Studien oftmals ein Wahlreaktionsparadigma verwendet. Allerdings ist zum einen die Auflösung der Methoden in der Elektrophysiologie relativ unpräzise, zum anderen stellen elektrophysiologischen Lokalisationsmethoden (BESA, LORETA) nur mathematische Lösungsmodelle dar. Die Kombination von der EEG mit der fMRT kann dieses Problem weitgehend lösen durch die Möglichkeit, EEG-Signal und fMRT-Signal auf der Ebene des Einzelereignisses zu verknüpfen (Debener et al. 2006). In dieser Studie soll dieses Verfahren erstmals für das N1-Zeitfenster angewandt werden.

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) may allow functional imaging of the brain at high temporal and spatial resolution. Artifacts generated in the EEG signal during MR acquisition, however, continue to pose a major challenge. Due to these artifacts, an interleaved modus has often been used for "evoked potential" experiments, i.e., only EEG signals recorded between MRI scan periods were assessed. An obvious disadvantage of this approach is the loss of a portion of the EEG information, which might be relevant for the specific scientific issue. In this study, continuous, simultaneous EEG-fMRI measurements were carried out. Visual evoked potentials (VEPs) could be reconstructed reliably from periods during MR scanning and in between successive scans. No significant differences between both VEPs were detected. This indicates sufficient artifact removal as well as physiological correspondence of VEPs in both periods. Simultaneous continuous VEP-fMRI recordings are thus shown to be feasible.

A major limitation of the routinely used clinical EEG lies in the ambiguous assignment of measured brain potentials to anatomic structures. By means of simultaneous EEG-fMRI the non-invasive imaging of structural correlates of EEG rhythms has become feasible, thus improving the interpretability of EEG findings. During MRI acquisition, however, large artifacts are induced in the EEG signal, making the physiological EEG unrecognizable. We employed a mathematical algorithm for artifact removal and validated this algorithm by means of visual evoked potentials (VEPs) recorded during and between MRI acquisition periods. We also showed the feasibility of MR imaging of physiological background rhythms like Alpha rhythm, functionally connected with the visual system, and sensorimotor Mu-rhythm. The MRI blood oxygenation level-dependent (BOLD) signal was negatively correlated with posterior Alpha rhythm in occipital areas, indicating deactivation in a metabolic sense. This result was confirmed by near infrared spectroscopy (NIRS), an optical method for monitoring local changes in deoxygenated hemoglobin concentration. Positive correlations between BOLD signal and Alpha activity in the thalamus indicate its generator role for this rhythm. For the 10- and 20-Hz components of the central Mu-rhythm we identified different cortical and subcortical representations. MR correlates of pathological EEG rhythms were investigated in patients with hepatic encephalography. Inevitable changes of vigilance during EEG-fMRI measurements, affecting EEG as well as BOLD signal, make simultaneous monitoring of vigilance necessary. A methodological approach is in progress with first results available.

Weak sensory stimuli can fully escape conscious perception and yet evoke minute electroencephalography (EEG) responses ([1][1]), indicating at least partial cortical processing of such “subliminal” input. We used functional magnetic resonance imaging (fMRI) during imperceptible electrical finger

We used simultaneous electroencephalogram-functional magnetic resonance imaging (EEG-fMRI) and EEG-near infrared spectroscopy (NIRS) to investigate whether changes of the posterior EEG alpha rhythm are correlated with changes in local cerebral blood oxygenation. Cross-correlation analysis of slowly fluctuating, spontaneous rhythms in the EEG and the fMRI signal revealed an inverse relationship between alpha activity and the fMRI-blood oxygen level dependent signal in the occipital cortex. The NIRS-EEG measurements demonstrated a positive cross-correlation in occipital cortex between alpha activity and concentration changes of deoxygenated hemoglobin, which peaked at a relative shift of about 8 s. Our data suggest that alpha activity in the occipital cortex is associated with metabolic deactivation. Mapping of spontaneously synchronizing distributed neuronal networks is thus shown to be feasible.

Functional magnetic resonance imaging (fMRI) was used to examine the influence of non-painful electrical stimulus intensity on the BOLD response in human primary somatosensory cortex (SI). In ten healthy subjects, index and middle finger of the right hand were stimulated separately at two different stimulus intensities. The activated volume of single finger representations as well as the volume of representational overlap of the two activations increased following an increase in stimulus intensity. This effect was seen in two different subdivisions of SI, one in the depth of the central sulcus, presumably corresponding to Brodmann area (BA) 3b, and one on the crown of the postcentral gyrus, presumably corresponding to BA 1/2. Relative overlap (ratio of overlap volume to volume of individual finger representation) was larger in BA 1/2 than in BA 3b. Additionally, in both areas relative overlap increased significantly from low to high stimulus intensity. Relative overlap did not change when different correlation thresholds were employed arguing against an unspecific 'spillover effect'. Analysis of signal intensity time courses indicated that the response difference to high versus low stimulus strength was not present during the initial seconds of stimulation, during which both led to a similar signal intensity increase. Only during the following maintenance level of the response did the response to high stimulus intensity reach a significantly higher plateau level than the one due to low intensity stimulation, an effect which was present in both areas, BA 3b and BA 1/2, respectively.