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.

Attentional effects in the timeframe of the event-related N1 potential have been described and addressed as „N1-effect“ more than thirty years ago. In the meantime this effect has been widely used as a tool to investigate attentional processes. While there has been some debate whether about the character of this phenomenon, e.g. in the sense of an overlapping „processing negativity“ on the basic and obligatory N1 potential, until recently no doubt has been formulated about the temporal lobe / auditory cortex origin of this effect. In the last years however, some hints exist for an additional contribution of the anterior cingulate cortex (ACC) to the N1 effect: Based on different source localization techniques like dipoles or LORETA, an ACC-generator of the N1 potential has been described. Very recently, an ACC-generator during the N1-timeframe has also been described using intracranial measurements. In the present study we used trial by trial coupling of simultameous EEG and fMRI to investigate the neural generators of the N1-potential in choice reaction tasks.

Currently, there is evidence demonstrating that schizophrenia is an illness characterized by multiple deficits in fundamental cognitive processes such as attention and memory. The P300 component of the event-related potential is thought to reflect various cognitive processes including the allocation of attentional resources to incoming stimuli. Reduction of the auditory P300 amplitude is constantly found in schizophrenic patients. Besides it could be shown that the P300 amplitude correlated negatively with the severity of thought disorders. Thus, the P300 appears to be a suitable functional parameter of thought disorders in schizophrenic patients. We combined ERP and functional MRI data to examine discrepancies in brain regions involved in information processing as well as in the time course of neural generators of the event-related potential between schizophrenics and normal controls. So far the study comprises six patients with schizophrenia and six age-matched controls with no known history of neurological or psychiatric disorder. The subjects performed an auditive oddball task requiring responses to infrequent tones presented in a series of frequent tones of a different pitch. MR imaging was performed on a 1.5 T Siemens Sonata scanner (EPI sequence; 12 slices; TR/TE: 3000/53 ms). EEG signals were recorded with an amplifier that cannot be saturated by MR activity (61 channels according to the international 10/10 system; Cz reference). The EEG recordings showed the expected positive deflection about 400 ms after the presentation of infrequent stimuli in normal controls and a reduced P300 component in schizophrenics. Besides we could replicate findings of previous P300 studies revealing BOLD activations mainly in frontal, especially anterior cingulate cortex, SMA, insula, inferior and middle frontal gyrus as well as thalamus, temporal and parietal brain structures in healthy subjects [Fig. 1]. The functional MRI data of schizophrenic patients showed a reduced BOLD response in a widespread network of cerebral areas involved in task execution [Fig. 2]. There was a modest negative correlation between the extent of functional activation in the ACC/SMA region and thought disorders as well as negative symptoms (PANSS) that did not reach significance. Our findings suggest widespread abnormal brain functioning in patients with schizophrenia during information processing.