Clinical features of Borderline Personality Disorder (BPD) as an unstable and dysregulated control over behavior, emotion, and cognition as well as clinical descriptions of temporary disturbances of perception and cognition led to the question of neuropsychological deficits. Although neuropsychological investigations of BPD did not provide a consistent constellation of findings, some evidence is available for a non-domain-specific impairment in multiple domains of memory, attention, visuo-spatial abilities and executive functioning (Fertuck et al., 2006). The clinical features of BPD and neuropsychological findings have been repeatedly discussed as reflecting prefrontal and temporo-limbic dysfunctions. Neuroimaging research provides support for alterations within these brain areas with respect to structure and function (Schmahl & Bremner, 2006). Although often reported neuropsychological outcomes have been repeatedly interpreted as reflecting prefrontal and temporo-limbic brain dysfunctions, these interpretations have to be preliminary since little is known about neurophysiological correlates of basic neuropsychological functions in BPD. With regard to the current state of research, it was considered that further neuropsychological research could benefit by considering three major principles: (i) The investigation of basic neuropsychological functions by the use of brain imaging methods, (ii) the inclusion of neuropsychological tasks with regard to emotional relevant stimuli and affect-laden processing, and (iii) the use of neuropsychological test that consider everyday demands. With regard to these considerations, the studies presented in this thesis aimed at the comprehensive investigation of verbal memory functioning in BPD.

The first study examined the neural correlates of verbal memory retrieval in BPD compared with non-psychiatric control subjects. Some prior neuropsychological findings argued for verbal memory malfunctioning in BPD. Furthermore, brain-imaging findings support alterations in prefrontal and limbic brain areas of BPD patients. Since these brain areas have been suggested to be crucial in both, episodic (memory for events and the surrounding context) and semantic memory (memory for facts / knowledge) retrieval (Cabeza & Nyberg, 2000; Markowitsch, 2005), these brain alterations may indicate general deteriorations in memory-related brain circuits. In an fMRI experiment, regional blood oxygenation level dependent (BOLD) signals were assessed during two experimental conditions of interest (episodic retrieval: 24-hour delayed recall of a wordlist; semantic retrieval: completing a lexical fluency task) and a low level baseline (listening to MRI noise) in 18 female right-handed BPD patients and 18 non-psychiatric control subjects matched with respect to sex, age, and education. It was hypothesized that BPD patients would show increased regional BOLD responses in prefrontal and limbic brain areas during both memory retrieval conditions. Although BPD patients and control subjects showed comparable performances in verbal episodic and semantic retrieval, important group differences in regional brain activation became evident. During the retrieval of episodic information, BPD patients showed patterns of increased task-specific regional BOLD responses as compared to controls in the posterior cingulate cortex (BA 23, 31) bilaterally, in the left middle (BA 21) and superior temporal (BA 22) gyri, in the right inferior frontal gyrus (BA 45) and in the right angular gyrus (BA 39). Further, control subjects compared with BPD patients did not show areas with increased BOLD responses. During the retrieval of semantic information, BPD patients as compared with control subjects showed areas of task-specific BOLD responses with respect to the right posterior cingulate cortex (BA 31), right fusiform gyrus (BA 37), left postcentral gyrus (BA 1,2,3) and the left anterior cingulate cortex (BA 24). Again, no areas of increased task-specific BOLD responses of control subjects compared with BPD patients could be found. Despite similar neuropsychological performances of BPD patients and control subjects in episodic and semantic memory tasks the day prior to scanning, the BPD patients showed, as hypothesized, patterns of increased brain activation. However, against the hypotheses, increased regional brain activation was not only evident in prefrontal and limbic brain areas but included further parietal areas. The increased regional brain suggests that BPD patients need to recruit additional cortical resources in order to successfully retrieve information. Thus, increased activation of BPD patients during retrieval might serve as compensation ("cognitive reserve capacity") to perform on a high level comparable to controls. Therefore, increased activation might indicate additional networks for adequate retrieval needed by BPD patients, i.e. increased effort, attention, working memory, or emotional control. However, it has to be noted that the results of the brain imaging study are limited to female patients with BPD since no male were included.

Study II examined the neuropsychology of verbal memory functioning in BPD. Most neuropsychological tests used neutral stimulus material to analyze verbal memory functioning whereas everyday requirements often include a variety of emotional relevant stimuli. Further, only few studies used verbal working memory tasks, which demand the control, and inhibition of interference as required in everyday demands. Limited evidence is available suggesting that BPD patients might show a reduced inhibition of emotionally relevant interference during memory tasks (Korfine & Hooley, 2000). For a closer investigation of the impact of interference on memory performance of BPD patients, a verbal learning/interference task was developed (Beblo, Mensebach et al., 2006). This task includes besides a learning condition without interference, conditions which utilize the presentation of additional stimuli of neutral and negative valence for interference purposes. With respect to the verbal/learning interference task, an interaction effect of learning condition (without interference, neutral valenced interference, negative valenced interference) and group (BPD patients, control subjects) on memory performance was expected. BPD patients were expected to show a decreased memory performance compared with control subjects if learning includes the control and inhibition of emotional negative interference, whereas their memory performance was expected to be comparable with control subjects regarding the learning conditions with neutral valenced interference and without interference. Besides the experimental verbal learning/interference task additional standard verbal memory tests covering verbal working memory, delayed memory and semantic memory were applied to control for possible impairment of the BPD patients with regard to standard conditions. 32 (21 females, 11 male) patients with BPD and 35 (23 females, 12 males) non-psychiatric control subjects matched with respect to sex, age, and intelligence took part. The results showed the hypothesized constellation of findings. Whereas memory performance of BPD patients were comparable with the control subjects regarding the learning conditions without interference and with neutral interference, BPD patients showed a significant decrease of memory performance as compared to control subjects in the condition with interference of negative valence. No group differences were found in the further neuropsychological tests, which were applied covering verbal working, delayed and semantic memory performance. These results suggest no general impairment of verbal memory functions in BPD. However, BPD may be characterized by a selective impairment of interference control and inhibition in BPD regarding emotional negative stimuli during learning.

The investigation of memory functioning with brain imaging method as well the inclusion of conditions, which require interference control and inhibition, can be characterized as helpful in the understanding of neuropsychological functions in BPD. The present findings may lead to the conclusion that verbal memory functioning is less severe than once thought. Furthermore, the efforts of the present studies made an important contribution to a more concrete determination of possible mechanisms that are impaired during the processing of memory tasks in BPD.

In sum, the present studies yielded three major findings: Verbal memory dysfunctions of BPD patients may be less severe impaired than once thought. The use of standard neuropsychological tests suggested no general impaired verbal memory functioning in BPD. However, BPD patients may use additional brain resources during the retrieval of verbal memory contents to perform on a level comparable to control subjects. Further, BPD patients show a reduced control for interference and inhibition during learning. More specifically, the reduced interference control and inhibition during verbal learning was restricted to emotionally relevant stimuli.