PUB - Publikationen an der Universität Bielefeld

This study was primarily concerned with the functional neuroanatomy underlying autobiographical memory. Functional magnetic resonance imaging (fMRI) was used to assess differences in the distributed networks of brain structures involved in the retrieval of old and new autobiographical memories with differential emotional valence. Additionally, a content analysis was accomplished to assess the thematic structure of emotional autobiographical memory in male and female healthy human subjects. Significant changes in neural activity related to autobiographical memory retrieval were observed bilaterally in medial and lateral temporal, temporal-occipital, posterior cingulate, and frontal cortices. Recent (relative to remote) memories were associated with differentially increased neural activity bilaterally in the retrosplenial cortex and the hippocampal region whereas remote (relative to recent) memories did not show any statistically significant differential neural activations. Positive (relative to negative) memories bilaterally activated the orbitofrontal cortex, the temporal pole, as well as medial temporal areas with the activation peak being in the entorhinal region. By contrast, negative (relative to positive) memories differentially increased neural activity in the right middle temporal gyrus only. No differences in behavioral performance were observed across experimental conditions. Analyses of gender specificities in the neural substrates of emotional autobiographical memory retrieval demonstrated that there were no overall differences in the autobiographical memory network in males and females, respectively. Also, there were no gender differences in behavioral performance. Analyses of gender differences associated with the main effect of TIME and EMOTION remained at a highly speculative level. The content analysis data showed significant differences in memory contents depending on both the age and the emotional valence of recollections. The neuroimaging data suggest differential functional roles for temporal, prefrontal and retrosplenial regions during autobiographical memory retrieval depending on the remoteness and the emotional valence of the memories retrieved. In particular, our findings support the "classic" model of long-term memory processing which suggests a time-limited differential involvement of the hippocampus in memory consolidation. Interestingly, the observation of such a time-dependent involvement of the hippocampal region in memory consolidation corresponds to the course of retrograde amnesia observed in demented patients, with the loss of recent memories appearing during early stages of the disease when conspicuous neurofibrillary changes are restricted mainly to the hippocampal and parahippocampal regions. Only during later stages, as the neurofibrillary changes spread out to neocortical association areas, remote memories become impaired, too. With regard to the effect of differential emotional valence of the memories retrieved, our data suggest that the entorhinal cortex and adjacent medial temporal areas (including the amygdala) are relatively more engaged in the processing of positive compared to negative emotion. Interestingly, this finding is in good accordance with recent research on emotion processing in patients with Alzheimer's disease (AD) indicating that early brain pathology within the entorhinal region specifically yields a deficit in the processing of positive information. Moreover, our results indicate that the neural substrates supporting emotional autobiographical memory retrieval are highly similar in males and females. This finding is consistent with the observation that there were not any significant gender differences in memory task performance. The content analysis data show differences as well as similarities in autobiographical memory contents across the experimental memory conditions suggesting that the topics referred to in autobiographical recollections vary with differential age and emotional valence of memories. However, this finding also demonstrates that some topics may play an overall significant role across an individual's whole life history.