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Christina Schmidt
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2013) 25 (11): 2003–2014.
Published: 01 November 2013
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Behavioral studies have cast doubts about the role that posttraining sleep may play in the consolidation of implicit sequence learning. Here, we used event-related fMRI to test the hypothesis that sleep-dependent functional reorganization would take place in the underlying neural circuits even in the possible absence of obvious behavioral changes. Twenty-four healthy human adults were scanned at Day 1 and then at Day 4 during an implicit probabilistic serial RT task. They either slept normally (RS) or were sleep-deprived (SD) on the first posttraining night. Unknown to them, the sequential structure of the material was based on a probabilistic finite-state grammar, with 15% chance on each trial of replacing the rules-based grammatical (G) stimulus with a nongrammatical (NG) one. Results indicated a gradual differentiation across sessions between RTs (faster RTs for G than NG), together with NG-related BOLD responses reflecting sequence learning. Similar behavioral patterns were observed in RS and SD participants at Day 4, indicating time- but not sleep-dependent consolidation of performance. Notwithstanding, we observed at Day 4 in the RS group a diminished differentiation between G- and NG-related neurophysiological responses in a set of cortical and subcortical areas previously identified as being part of the network involved in implicit sequence learning and its offline processing during sleep, indicating a sleep-dependent processing of both regular and deviant stimuli. Our results suggest the sleep-dependent development of distinct neurophysiological processes subtending consolidation of implicit motor sequence learning, even in the absence of overt behavioral differences.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2011) 23 (1): 26–40.
Published: 01 January 2011
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Memory is constructive in nature so that it may sometimes lead to the retrieval of distorted or illusory information. Sleep facilitates accurate declarative memory consolidation but might also promote such memory distortions. We examined the influence of sleep and lack of sleep on the cerebral correlates of accurate and false recollections using fMRI. After encoding lists of semantically related word associates, half of the participants were allowed to sleep, whereas the others were totally sleep deprived on the first postencoding night. During a subsequent retest fMRI session taking place 3 days later, participants made recognition memory judgments about the previously studied associates, critical theme words (which had not been previously presented during encoding), and new words unrelated to the studied items. Sleep, relative to sleep deprivation, enhanced accurate and false recollections. No significant difference was observed in brain responses to false or illusory recollection between sleep and sleep deprivation conditions. However, after sleep but not after sleep deprivation (exclusive masking), accurate and illusory recollections were both associated with responses in the hippocampus and retrosplenial cortex. The data suggest that sleep does not selectively enhance illusory memories but rather tends to promote systems-level consolidation in hippocampo-neocortical circuits of memories subsequently associated with both accurate and illusory recollections. We further observed that during encoding, hippocampal responses were selectively larger for items subsequently accurately retrieved than for material leading to illusory memories. The data indicate that the early organization of memory during encoding is a major factor influencing subsequent production of accurate or false memories.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2007) 19 (4): 671–683.
Published: 01 April 2007
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We aimed at investigating social disability and its cerebral correlates in frontotemporal dementia (FTD). To do so, we contrasted answers of patients with early-stage FTD and of their relatives on personality trait judgment and on behavior prediction in social and emotional situations. Such contrasts were compared to control contrasts calculated with answers of matched controls tested with their relatives. In addition, brain metabolism was measured in patients with positron emission tomography and the [ 18 F]fluorodeoxyglucose method. Patients turned out to be as accurate as controls in describing their relative's personality, but they failed to predict their relative's behavior in social and emotional circumstances. Concerning the self, patients were impaired both in current personality assessment and in prediction of their own behavior. Those two self-evaluation measures did not correlate. Only patients' anosognosia for social behavioral disability was found to be related to decreased metabolic activity in the left temporal pole. Such results suggest that anosognosia for social disability in FTD originates in impaired processing of emotional autobiographical information, leading to a self-representation that does not match current behavior. Moreover, we propose that perspective-taking disability participates in anosognosia, preventing patients from correcting their inaccurate self-representation based on their relative's perspective.