Everyday life experience tells us that individual differences apparently matter. Although confronted with the same situation, individuals seem to act and react in different ways. On a behavioral and self-report level, individual differences are well documented. Over the past decades, they have been systematically assessed and embedded in complex theories of personality. On the other hand, the influence of personality differences on cognitive processes and their cerebral substrate is far from being entirely understood. Especially the complex interplay of two or more aspects, like individual differences (e.g., in motivational processes), cognitive functions (e.g., intuition), cerebral activation and lateralization, and humoral processes (e.g., cortisol), are seldom aim of psychological research. The Personality Systems Interaction (PSI) theory (Kuhl, 2000, 2001) provides a theoretical framework, which tries to incorporate the above-mentioned aspects. On the background of PSI theory, the aim of the present work was to investigate differences in motivational processing and how they are related to hemispherical asymmetries, cognitive processing, and humoral reactivity. Each of the three research articles presented throughout the present work tackles different aspects of this general research question. For this, a variety of different methodological techniques were used (e.g., questionnaires, implicit measures, electroencephalography, etc.) to approach the aforementioned goal. The first research paper presented in the current work examines the relationship between the implicit affiliation motive and intuition, as a form cognitive processing. Previous research already demonstrated that affiliation-laden primes facilitate intuitive thought (Kuhl & Kazén, 2008). Therefore, it could be expected that trait affiliation motive would also be correlated with intuition. Intuition in turn is thought to be a function of right hemispheric processes. An association between trait affiliation and intuition could therefore indirectly indicate a lateralization to the right side for affiliation. With the first study of the present work, the author tested this association. Thirty-nine students filled in the Operant Motive Test for the assessment of implicit affiliation, a variant of the Thematic Apperception Test. Then, 9 months later, participants engaged in a Remote Associates Test in which they intuitively had to indicate whether three words are semantically related. As expected, the implicit affiliation motive significantly predicted the accuracy of identifying related word triads. No other implicit or explicit measure, nor state or trait positive affect was associated with intuition. With the second research article, the aforementioned indirect association between affiliation and lateralized processing was investigated more directly. Previous research on relationships between personality and EEG resting state frontal asymmetries mainly focused on individual differences with respect to motivational direction (i.e., approach vs. withdrawal). By contrast, the second article investigated frontal asymmetries as a function of individual differences in implicit affiliation motive. The goal was not only to contribute to the validation of PSI theory and to the investigation of the laterality of the affiliation motive, but also to disentangle the contribution of different social motives to frontal EEG asymmetries. The consideration of social motives, such as the affiliation motive, seemed to be necessary, because a recent meta-analysis showed that the association between approach motivation and frontal asymmetries is negligible or that unidentified moderators drive this association. From previous research and the results from the first paper presented in the current work, an association between affiliation motive and right frontal activity was predicted. Additionally, to control for possible associations with motivational direction, trait behavioral inhibition, behavioral activation, and anger were assessed and correlated with frontal asymmetries. Seventy-two right-handed students were tested. As expected and in accordance with the findings from the first paper, the author found that relative right frontal activity (indicated by low alpha frequency power) was associated with the affiliation motive. To explore brain regions responsible for this association at scalp sites, a source localization algorithm was applied. Intracranial distribution of primary current densities for the alpha band spectrum in source space was estimated and correlated with implicit affiliation scores. A significantly correlating area could be identified in the right ventromedial prefrontal cortex (Brodmann Area 10). No other associations at scalp sites or in source space could be found for motivational direction. The third research article presented in the current work highlights motivational differences slightly different from those presented above. It deals with dynamic motivational processes, such as action orientation, and how they moderate the association between cerebral asymmetries and the physiological stress reaction. Hypothalamus pituitary adrenocortical (HPA) system activity and frontal brain asymmetries have both been linked to stress and emotion but their relationship remains unclear, especially when additionally considering individual differences. Therefore, participants were exposed to public speaking stress while salivary cortisol levels (as a marker of HPA activity) and resting frontal EEG alpha asymmetries were assessed before and after stress induction. The results indicate that higher post stressor cortisol levels were associated with higher relative left frontal activity. State oriented participants showed a stronger association between cortisol response and left frontal activity than action oriented participants. The above-mentioned findings are discussed referring to PSI theory and their possible implications. Additionally, shortcomings of the present research and possible remedies will be presented.

Trotz zahlreicher Untersuchungen lässt sich bei der Zwangsstörung noch kein einheitliches, alle Befunde integrierendes Krankheitsmodell formulieren. Die Verarbeitung von emotionalen Reizen könnte bei Personen mit Zwangsstörungen verändert sein. Dies trägt möglicherweise zur Entwicklung und Aufrechterhaltung der Störung bei. Das Ziel der vorliegenden Arbeit war es, spezifische Komponenten dieser Verarbeitung zu untersuchen. Zuerst wurde in zwei unterschiedlichen Studien überprüft, ob die Orientierung der Aufmerksamkeit zu neuen Reizen bei Patienten mit Zwangsstörungen verstärkt ist. Zu diesem Zweck wurden durch neue Reize evozierte Potentiale im Elektroenzephalogramms (EEG) gemessen. Anschließend wurde in einer Studie überprüft, ob das Verhältnis der Aktivierungen von dem Vermeidungs- zum Annäherungssystem bei den Betroffenen verändert ist. Dies lässt sich an Hand der Ermittlung der hemisphärischen Verteilung von Alpha-Wellen in frontalen Hirnregionen feststellen. Die Ergebnisse der ersten beiden Studien ergaben, dass Patienten unabhängig vom emotionalen Kontext eine stärkere Aufmerksamkeitshinwendung zu neuen Reizen zeigen (Studie 1), was allerdings nicht beobachtet wurde, wenn die neuen Reize innerhalb des Aufmerksamkeitsfokus lagen (Studie 2). Dieses Ergebnis wurde als überaktives Gefahrenerkennungssystem bei Patienten interpretiert. Weiterhin ließ sich feststellen, dass Patienten im Vergleich zu gesunden Kontrollen in frontalen Hirnregionen eine Verlagerung der Alpha Asymmetrie zur linken Gehirnhemisphäre aufwiesen (Studie 3). Dieser Befund wurde unabhängig von einer Stimulierung durch emotionale Reize gemacht. Er lässt sich als stärkere Aktivierung des Vermeidungs- im Verhältnis zum Annäherungssystem deuten. Zusammengefasst zeigte sich bei Patienten mit Zwangsstörungen eine veränderte Verarbeitung von emotionalen Reizen. Aus diesen Befunden können spezifische Empfehlungen für die Behandlung der Störung abgeleitet werden. / It is so not possible to formulate a disease model of obsessive-compulsive disorder (OCD) that integrates all the results of the many studies carried out. The neural processing of emotional stimuli might be altered in people with OCD. This might play an important role in the development and maintenance of OCD. The present work aimed to investigate specific components of the neural processing of emotional stimuli. The first two studies examined if the orienting of attention towards novel stimuli is enhanced in patients with OCD. For this purpose the event-related brain potentials evocated by novel stimuli in the electroencephalogram were recorded. The third study tested if the relationship between the withdrawal-avoidance mode and the approach mode of the motivational brain system is altered in OCD patients. This can be assessed by the hemispheric distribution of alpha power in frontal brain regions. The results of the first two studies showed that the orienting of attention towards novel stimuli is enhanced in patients with OCD independently of the emotional context condition (study 1), which could not be observed if the novel stimuli were listened to in active attentional mode (study 2). This was interpreted as a hypersensitive threat detection system. Further, it was found that patients showed a shift of frontal alpha activity to the left hemisphere compared to healthy control subjects (study 3). This result was independent of the viewing of emotional stimuli. It can be concluded that the avoidance mode is relatively increased in patients with OCD. Taken together, patients showed an altered neural processing of emotional stimuli. Specific recommendations for he treatment of the disorder can be drawn out of them.

Severe motor vehicle accidents (MVAs) represent one of the most often occurring psychological traumas, and are a leading cause of Posttraumatic Stress Disorder (PTSD). However, not all persons develop PTSD after traumatic events and a great proportion of patients who show symptoms initially recover over time. This has stimulated research of psychological and biological factors that explain development and maintenance of the disorder. Fortunately, this highly distressing condition can be effectively treated, e.g. via cognitive behavioral therapy (CBT). However, brain mechanisms underlying changes due to psychological therapy in PTSD are almost unknown (Roffman, Marci, Glick, Dougherty, & Rauch, 2005). On the other hand there are observations of positive changes following trauma called Posttraumatic Growth (PTG), which have stimulated research of associated psychological processes and factors. However, there is a lack of research about the relation of biological variables (e.g. measures of brain function) and PTG. Theories of brain asymmetry and emotion (Davidson, 1998b, 2004b; Heller, Koven, & Miller, 2003) propose that asymmetries of brain activation are related to certain features of human emotion (e.g. valence, approach or withdrawal tendencies, arousal). Whereas an enormous increase in the understanding of structural and functional abnormalities in PTSD could be achieved in the last decades due to neuroimaging research, there are still numerous unanswered questions. Especially, there is only little research explicitly examining activation asymmetries in PTSD. Furthermore, as mentioned, research is sparse investigating alterations of brain function that are associated with successful psychological treatment of PTSD. Finally, there is no published study examining how measures of brain function are related to PTG. This thesis presents 3 studies investigating electroencephalographic (EEG) asymmetries in survivors of severe motor vehicle accidents. The first part of the thesis (chapter 2) is devoted to a literature review about description (chapter 2.1), epidemiology (chapter 2.2 and 2.3), risk factors (chapter 2.4), psychological theories (chapter 2.5), biological mechanisms particularly neuroimaging findings (chapter 2.6), and treatment of PTSD (chapter 2.7.). Chapter 2.8 gives a short review on definition and research of Posttraumatic Growth. Chapter 2.9 provides an overview of models and research regarding brain asymmetry and emotion. In chapter 3.1, a study is presented that investigated hemispheric asymmetries (EEG alpha) among MVA survivors with PTSD, with subsyndromal PTSD, and without PTSD as well as non-exposed healthy controls during a baseline condition and in response to neutral, positive, negative, and trauma-related pictures (study I). Next, the findings of study II are presented (chapter 3.2). This study examined the effect of cognitive behavioral therapy on measures of EEG activity. Therefore, EEG activity before and after CBT in comparison to an assessment only Wait-list condition was measured. In chapter 3.3 a correlational study (study III) is presented that examined the relationship between frontal brain asymmetry and selfreported posttraumatic growth after severe MVAs. Finally, in chapter 4 the findings are summarized and discussed with respect to (1) the state/trait debate in frontal asymmetry research and (2) current psychological theories of PTSD and PTG. In addition, the use of neuroscientific research for psychotherapy is discussed. Suggestions are presented for future goals for “brain” research of PTSD and treatment of PTSD. / Schwere Verkehrsunfälle stellen eines der am häufigsten vorkommenden psychologischen Traumata dar, und sind eine Hauptursache der Posttraumatischen Belastungsstörung (PTBS). Jedoch entwickeln nicht alle Personen nach traumatischen Ereignissen eine PTBS und bei einem Großteil remittieren anfängliche PTBS-Symptome. Dies stimulierte die Erforschung von psychologischen und biologischen Faktoren, die die Entstehung und Aufrechterhaltung der PTBS erklären. Glücklicherweise kann die PTBS effektiv, z.B über die kognitive Verhaltenstherapie (KVT), behandelt werden. Jedoch sind Gehirnmechanismen, die mit klinischen Änderungen aufgrund der psychologischen Therapie in PTSD einhergehen, nahezu unbekannt (Roffman, Marci, Glick, Dougherty, Rauch, 2005). Auf der anderen Seite gibt es Berichte von positiven Änderungen nach traumatischen Ereignissen, die als Posttraumatische Reifung (PTR) bezeichent werden. Dies hat in kürzerer Vergangenheit die Forschung von verbundenen psychologischen Prozessen und Faktoren stimuliert. Jedoch gibt es kaum Untersuchungen über die Beziehung von biologischen Variablen (z.B Messungen der Gehirnfunktion) und PTR. Diese Arbeit präsentiert 3 Studien, die electroenzephalographische (EEG) Asymmetrien bei Opfern schwerer Verkehrsunfälle untersuchten. Der erste Teil der Arbeit (Kapitel 2) widmet sich einer Literaturrezension über: die Beschreibung (Kapitel 2.1), Epidemiologie (Kapitel 2.2 und 2.3), Risikofaktoren (Kapitel 2.4), psychologische Theorien (Kapitel 2.5), biologische Mechanismen besonders Neuroimaging Ergebnisse (Kapitel 2.6), und Behandlung der PTBS (Kapitel 2.7.). Kapitel 2.8 gibt einen kurzen Überblick über die Definition und Forschung zur Posttraumatischen Reifung. Kapitel 2.9 gibt eine Übersicht zu aktuellen Modellen und empirischen Befunden bezüglich Gehirnasymmetrien und Emotionen. Kapitel 3.1 präsentiert eine Studie, in der hemisphärische Asymmetrien (im EEG-Alpha Band) bei Unfallopfern mit PTBS, subsyndromaler PTBS, und ohne PTBS sowie gesunden Kontrollpersonen ohne Unfall untersucht wurden: während einer Ruhemessung und einer Emotionsinduktions-bedingung (neutrale, positive, negative und trauma-spezifische Bilder) (Studie I). Danach werden die Ergebnisse der Studie II (Kapitel 3.2) präsentiert. Hier wurde die Wirkung der kognitiven Verhaltenstherapie auf Messungen der EEG-Aktivität untersucht. Deshalb wurde EEG-Aktivität vor und nach einer KVT im Vergleich mit einer Warten-Gruppe gemessen. Kapitel 3.3 präsentiert eine Korellationsanalyse (Studie III), bei der die Beziehung zwischen der frontalen Gehirnasymmetrie und posttraumatischer Reifung untersucht wurde. Am Ende der Arbeit (Kapitel 4) werden die Ergebnisse zusammengefasst und in Bezug auf (1) die state/trait-Debatte im Rahmen der Asymmetrie-Forschung diskutiert sowie (2) ein Bezug zu aktuellen psychologische Theorien von PTSD und PTG hergestellt. Außerdem wird der Nutzen von neurobiologischer Forschung für die Psychotherapie besprochen. Dabei werden Vorschläge für zukünftige Projekte für die "Gehirn"-Forschung im Zusammenhang mit der PTBS, deren Behandlung und PTG gemacht.