On cognitive, emotional and clinical aspects of source-monitoring: Functional MRI findings.
Source monitoring refers to the process of identifying the origin of information in memory or thought. Central to this process is the combination of separate pieces of information into relational representations, referred to as relational memory. The current project investigated the neural and behavioral correlates of source monitoring and relational memory using functional Magnetic Resonance Imaging (fMRI).
Long-term relational memory is one suggested functional role of the hippocampus within the medial temporal lobe (MTL). Recent research suggests that the hippocampus also play a functional role with respect to short-term relational memory. However, it is not clear whether the role during short retention intervals is because the hippocampus serves a specific binding function or whether its involvement is related to capacity issues. Whether hippocampus serves a specific binding function was studied by varying the levels of cognitive workload in a short-term relational memory fMRI paradigm. The findings indicate that the functional role of hippocampus is associated with high cognitive workload, and not short-term relational memory per se. Short-term relational memory was to a larger extent associated with a region within the MTL (parahippocampal gyrus). This suggests that the hippocampus may be involved if organizational processing of short-term retention of relational representations is insufficient.
Emotional arousal seems to facilitate memory in general. This effect has partially been explained by engagement of the amygdala, which may in turn modulate other regions, such as hippocampus, to facilitate memory processes. However, it is debated whether arousal facilitates or impedes relational memory and monitoring processes, and which aspects of an event may be facilitated by arousal. By using subjective levels of arousal during a short-term relational memory fMRI paradigm the neural and behavioral effects of emotional arousal on processing of relational representations were investigated. The findings indicate that arousal facilitates short-term relational memory, and may do so by enhancing distinctiveness during encoding. The fMRI results further indicate that arousal modulates higher-order visual areas, amygdala and hippocampus in a dose-dependent manner. This suggests that short-term relational memory may be facilitated by subjective emotional arousal, and that this is accompanied by a dose-dependent response in neural regions central to memory performance.
Psychotic symptoms indicate an underlying impairment with respect to differentiating internally (i.e. self-generated information such as thoughts, beliefs or imaginations) from externally (i.e. information generated outside the individual) generated information, a process referred to as reality monitoring. It has been suggested that correct monitoring of the origin of information depends, in part, on relational memory, and failure may lead to misattribution of the origin of the information, and consequently leading to psychotic symptoms. Results from our study showed that patients with schizophrenia spectrum disorder display a specific, weakened identification of internally generated information, which was negatively correlated with severity of delusions. The reduced identification of internally generated information was accompanied by hypoactivity in fronto-temporal brain regions, and neural activity in the left hippocampus was negatively associated with severity of delusions. The findings suggest that impaired monitoring processes may be one component in the development and maintenance of delusions, and that this impairment may be mediated by abnormal relational memory.