UittrekselHarm avoidance (HA) is a personality trait describing one’s tendency to inhibit ac-tions due to expected risks for a negative outcome or personal harm. This trait is closely related to one’s vulnerability for mood and anxiety disorders (e.g. depres-sion). In this thesis, we tested the hypothesis that HA is related to how the brain processes emotional stimuli and to brain morphology. In particular, we expected to find increasing neural responses to negative stimuli in the amygdalae (key centers in processing emotional, and in particular anxious, stimuli and in initiating negative, avoidant reactions) and that the size of the amygdalae is increased in individuals scoring high on HA. Additionally, we tested the robustness of the found increased activity for variations in used functional MRI (fMRI) task. Likewise, the repeatability of the found correlations between brain morphology and HA were tested despite var-iations in chosen processing settings (voxel-based morphology (VBM) or region-of-interest (ROI) labeling, smoothing filter, regression model, brain atlas and multiple comparisons correction method). To limit confounding effects of age and gender, all studies were performed on healthy, young females only.
First, we performed three functional magnetic resonance imaging (fMRI) studies. In the first fMRI study we used a passive viewing task. In the second study we used a passive viewing task while focusing on the own emotions. In the last fMRI study, we asked the participants to rate the emotional valence of the presented stimuli explicit-ly. Secondly, we performed two similar VBM studies. Additionally, in the second VBM study, we repeatedly analyzed the data while changing the processing settings and the VBM results were compared to those from ROI labeling.
Our studies revealed that individual differences in neural processing and brain mor-phology in the prefrontal, limbic, temporal and visual cortices could be related to dif-ferences in HA. Moreover, our fMRI studies revealed that the emotional responses to negative stimuli in the amygdala relate to HA, but that this effect is task dependent. A relation between HA and regional volumetry, was not observed. Moreover, our se-cond morphology study showed that the outcome of this kind of VBM studies largely depends on the used analysis settings. In particular, the included or excluded pa-rameters in the regression model seems to affect the final study outcome. From our VBM studies, it seems worth to include at least all other personality traits from Clon-inger’s psychobiological model of personality (NS, RD, P, SD, CO and ST) in the re-gression model optimization.
We concluded that individual differences in brain morphology and emotional pro-cessing could partly be related to HA, but that we failed to show such a relation with HA consistently in the amygdalae. Partially, this inconsistency seems to come from task dependent interactions between the amygdala and other areas in the brain dur-ing the fMRI studies and from the effects of many other factors, such as the other personality traits, on brain morphology.
|Datum Prijs||21 apr 2016|
|Begeleider||Chris Baeken (Promotor), Johan De Mey (Promotor), Mark De Ridder (Jury), Mieke Cannie (Jury), Nico Buls (Jury), Hubert Raeymaekers (Jury), U. Dannlowski (Jury) & R Peeters (Jury)|