Recent studies indicate that medial-temporal lobe (MTL) damage, either from focal lesions or neurodegenerative disease (e.g., semantic dementia), impairs perception as well as long-term declarative memory. Notably, however, these two patient groups show different performance for meaningful versus unfamiliar stimuli. In amnesics with nonprogressive MTL lesions, the use of meaningful stimuli, compared with unfamiliar items, boosted discrimination performance. In semantic dementia, a condition characterized by progressive deterioration of conceptual knowledge in the context of anterolateral temporal lobe damage, performance for meaningful stimuli was equivalent to that for unfamiliar items. To further investigate these findings, we scanned healthy volunteers while they performed odd-one-out discriminations involving familiar (i.e., meaningful/famous) and unfamiliar (i.e., novel) objects and faces and a baseline task of size oddity. Outside the scanner, volunteers' recognition memory was assessed. We found above baseline activity in the perirhinal cortex and hippocampus for all object and face discriminations and above baseline activity in the temporal pole for all face discriminations. The comparison of meaningful, relative to novel, faces and objects, revealed increased activity in the perirhinal cortex and hippocampus. In the temporal pole, we also found activity related to meaningfulness for faces but not for objects. Importantly, these meaningfulness effects were evident even for discriminations that were not subsequently well remembered, suggesting that the difference between meaningful and novel stimuli reflects perceptual or conceptual processes rather than solely incidental encoding into long-term memory. The results provide further evidence that the MTL is recruited during complex perceptual discrimination and additionally suggest that these structures are recruited in semantic processing of objects and faces.

Face processing in the human brain recruits a widespread cortical network based mainly in the ventral and lateral temporal and occipital lobes. However, the extent to which activity within this network is driven by different face properties versus being determined by the manner in which faces are processed (as determined by task requirements) remains unclear. We combined a functional magnetic resonance adaptation paradigm with three target detection tasks, where participants had to detect a specific identity, emotional expression, or direction of gaze, while the task-irrelevant face properties varied independently. Our analysis focused on differentiating the influence of task demands and the processing of stimulus changes within the neural network underlying face processing. Results indicated that the fusiform and inferior occipital gyrus do not respond as a function of stimulus change (such as identity), but rather their activity depends on the task demands. Specifically, we hypothesize that, whether the task encourages a configural- or a featural-processing strategy determines activation. Our results for the superior temporal sulcus were even more specific in that we only found greater responses to stimulus changes that may engage featural processing. These results contribute to our understanding of the functional anatomy of face processing and provide insights into possible compensatory mechanisms in face processing.

Reality monitoring refers to the process of discriminating between internally and externally generated information. Two different tasks have often been used to assess this ability: (a) memory for perceived versus imagined stimuli; and (b) memory for participant- versus experimenter-performed operations. However, it is not known whether these two reality monitoring tasks share neural substrates. The present study involved use of a within-subjects functional magnetic resonance imaging design to examine common and distinct brain mechanisms associated with the two reality monitoring conditions. The sole difference between the two lay in greater activation in the medial anterior prefrontal cortex when recollecting whether the participant or the experimenter had carried out an operation during prior encoding as compared to recollecting whether an item had been perceived or imagined. This region has previously been linked with attending to mental states. Task differences were also reflected in the nature of functional connectivity relationships between the medial anterior and right lateral prefrontal cortex: There was a stronger correlation in activity between the two regions during recollection of self/experimenter context. This indicates a role for the medial anterior prefrontal cortex in the monitoring of retrieved information relating to internal or external aspects of context. Finally, given the importance of reality monitoring to understanding psychotic symptoms, brain activity was related to measures of proneness to psychosis and schizotypal traits. The observation of significant correlations between reduced medial anterior prefrontal signal and scores on such measures corroborates these theoretical links.

Based on an event-related potential study by Rugg et al. [Dissociation of the neural correlates of implicit and explicit memory. Nature, 392, 595-598, 1998], we attempted to isolate the hemodynamic correlates of recollection, familiarity, and implicit memory within a single verbal recognition memory task using event-related fMRI. Words were randomly cued for either deep or shallow processing, and then intermixed with new words for yes/no recognition. The number of studied words was such that, whereas most were recognized (“hits”), an appreciable number of shallow-studied words were not (“misses”). Comparison of deep hits versus shallow hits at test revealed activations in regions including the left inferior parietal gyrus. Comparison of shallow hits versus shallow misses revealed activations in regions including the bilateral intraparietal sulci, the left posterior middle frontal gyrus, and the left frontopolar cortex. Comparison of hits versus correct rejections revealed a relative deactivation in an anterior left medial-temporal region (most likely the perirhinal cortex). Comparison of shallow misses versus correct rejections did not reveal response decreases in any regions expected on the basis of previous imaging studies of priming. Given these and previous data, we associate the left inferior parietal activation with recollection, the left anterior medial-temporal deactivation with familiarity, and the intraparietal and prefrontal responses with target detection. The absence of differences between shallow misses and correct rejections means that the hemodynamic correlates of implicit memory remain unclear.