Borderline Personality disorder (BPD) is a serious psychiatric disorder and the most prominent features are emotional instability, interpersonal disturbances, chronic emptiness and chronic suicidal tendencies (Linehan et al., 1993). BPD patients have a pattern of high psychiatric service use. The debate regarding the neurobiological mechanisms underlying BPD is still ongoing, and therefore identification of biomarkers would be a major step toward improving diagnostic accuracy and identifying therapeutic targets (Stanley and Siever, 2010). A common way to study the emotional instability of BPD is the measurement of responses after presentation of emotional stimuli. Faces convey information that is essential for interpersonal interactions and emotional expressions play a central role, since they are crucial for inferring the observed person's feelings and intentions. A substantial number of behavioral studies have investigated emotional face recognition in patients with BPD, but they demonstrated heterogeneous results. So far, researchers used static images, i.e. Ekman faces and in these studies, BPD patients were able to correctly identify emotional expressions at times more accurately than healthy controls (Domes et al., 2008, Lynch et al., 2006 and Vuilleumier and Pourtois, 2007). However, when facial emotion recognition tasks present more complex situations, by setting time limits for recognizing emotions in faces (Dyck et al., 2009), or with additional prosodic information (Minzenberg et al., 2006), patients with BPD showed increased error rates. The study by Lynch et al. (2006) used a morphing affect recognition paradigm with several emotion intensities and showed a “hyper-responsiveness” for patients with BPD especially towards fearful faces (Lynch et al., 2006). Imaging studies in BPD have shown fusiform gyrus, as well as amygdala, inferior and middle temporal cortical areas hyperactivity during emotional face expression tasks (Guitart-Masip et al., 2009 and Herpertz et al., 2001).
To date, the temporal dynamics of brain responses to emotional faces in BPD still remain unclear (Vuilleumier and Pourtois, 2007). Electrophysiological investigations in the primary visual or extra-striate cortex concerning the fundamental, visual-perceptive process of patients with BPD are sparse. An opportunity to measure the distinctive temporal electrophysiological responses towards face processing in vivo and non-invasively exists in the form of magnetoencephalography (MEG), a technique known for its excellent temporal resolution. A face-specific, event-related magnetic field (ERF) peaking at 170 ms (M170) post stimulus and recorded at posterior sensors corresponds to the right inferior occipito-temporal cortex (Deffke et al., 2007 and Halgren et al., 2000). An even faster cortical response to the coarse recognition of faces in healthy subjects has been found as early as 100 ms (M100) (Liu et al., 2002). The “fusiform face area” (FFA) has been defined as an extrastriate module for face perception (Kanwisher et al., 1997). Posterior to the FFA, the “occipital face area” (OFA) (Gauthier et al., 2000), has been observed to respond preferably to faces than objects. The rOFA has been shown to be mandatory for recognition of face parts and emotional expressions after temporary lesions were produced in this area by applying repetitive transcranial magnetic stimulation (rTMS) (Pitcher et al., 2008).
Thus, the purpose of our study was to investigate if BPD patients, compared with healthy controls, show electrophysiological differences in the early visual processing pathways, represented as M170 in the occipito-temporal visual cortices areas while processing faces and other stimuli. The study is focused on the early visually evoked fields as they are known to yield stable MEG responses. The perception of facial expression implicates a large neural network (Adolphs et al., 2003) and the investigation of the ventral visual pathway in patients with BPD contributes to the understanding of an affect-sensitive network, which has not been assessed so far by MEG.
The current study implemented two visual processing tasks using different kinds of response formats. In the first task, subjects had to silently watch three stimulus categories: faces, houses and animals. With this simple task, we investigated electrophysiological responses to basic visual stimuli. The second task was an emotion-specific task in which subjects had to judge emotions within a distinct time limit. On the electrophysiological level, we expected differences between the two groups but had a non-directional differential hypothesis due to lacking prior MEG data with BPD patients. As BPD patients seem to have problems predominantly with the perception of the emotions fear and anger (Koenigsberg et al., 2002 and Levine et al., 1997), we hypothesized differences in the perception of those negative emotions in patients with BPD compared to healthy controls in the behavioral task. Further, to address the issue of patients with BPD being a heterogeneous diagnostic group, we controlled for comorbid diagnoses, especially for comorbid post-traumatic stress disorder (PTSD) and major depression. Finally, we controlled for dissociation by implementing a dissociation rating during the MEG measures.
