Biomedical subjects

Francis Eustache

Publications and source records attributed to Francis Eustache.

35 records · Page 2Linked to original sources

PubMed2005

Semantic memory disorders in Alzheimer's disease: clues from semantic priming effects.

Semantic memory deficits are a common landmark in Alzheimer's disease, but the nature of these impairments remains to be clarified. The tests used to explore this memory system are not specific and involve cognitive processes often disturbed in Alzheimer's disease. A complementary way to investigate semantic memory in neuropsychology is by using the semantic priming paradigm. Here, semantic priming refers specifically to the modification of a stimulus processing behind the presentation of a related stimulus; it is a short-lived phenomenon considered an implicit measure of semantic memory integrity. However, semantic priming studies have yielded contradictory results in Alzheimer's disease, with authors reporting normal priming, less-than-normal priming, or increased priming effects (hyperpriming). The aim of this paper is to review the literature investigating semantic priming in Alzheimer's disease, and to discuss the contradictory results in the context of current models of semantic processing. For a clear comprehension of the semantic priming patterns in this pathology, we will precise the methodology used and the characteristics of the Alzheimer's disease patients examined. Besides, the surprising hyperpriming phenomenon - often observed in Alzheimer's disease at the early stage of dementia--will also be explained in detail. These results from semantic priming represent invaluable clues to widen our knowledge and conceptions about deterioration of the semantic memory in Alzheimer's disease.

Alzheimer Disease↗

PubMed2004

Consolidation of strictly episodic memories mainly requires rapid eye movement sleep.

STUDY OBJECTIVES: The aim of this study is to examine the effects of sleep deprivation during the first or second half of the night on episodic memory consolidation. Episodic memory is defined as memory for events located in time and space. It is also characterized by autonoetic consciousness, which gives a subject the conscious sensation of traveling back in time to relive the original event and forward into the future. DESIGN: Consolidation of episodic information was tested after 4-hour retention intervals, which followed learning and occurred during either the early or late half night, respectively dominated by slow wave sleep (SWS) or rapid eye movement (REM) sleep, or corresponding periods of wakefulness. SETTING: Data collection occurred in the sleep laboratory. PARTICIPANTS: Forty-three young healthy subjects: 9 men and 34 women, age ranging from 18 to 26 years (mean 20.18 +/- 1.94 years) were included in this study. INTERVENTIONS: Waking after a 4-hour retention interval filled with early or late sleep, or 4-hour sleep deprivation, during early or late period of night. MEASUREMENTS AND RESULTS: The cognitive task, named the What-Where-When test, was specially designed to assess factual, spatial, and temporal components of episodic memory. This task was associated with the Remember/Know paradigm to assess autonoetic consciousness. We measured performance on immediate free recall, delayed free recall (after a 4-hour interval of wakefulness or sleep), and delayed recognition. We also calculated a forgetting rate for each feature (factual, spatial, and temporal) and, for the recognition task, scores of autonoetic consciousness (R responses). REM-sleep deprivation was associated with significantly lower recall of spatial information compared to SWS deprivation (P < .01) or late sleep (P < .05) conditions. REM-sleep deprivation was also associated with a higher forgetting rate of temporal information as compared to the early sleep condition (P< .01). Finally, REM-sleep deprivation led subjects to give significantly fewer R responses, indicative of true memories, as compared to SWS deprivation (P < .05). CONCLUSIONS: These results suggest that consolidation of truly episodic memories mainly involves REM sleep.

Adolescent↗

PubMed2004

'In the course of time': a PET study of the cerebral substrates of autobiographical amnesia in Alzheimer's disease.

Neuroimaging studies in healthy subjects have yielded controversial results about the neural substrates of autobiographical memory. Moreover, the neural networks responsible for autobiographical amnesia remain poorly understood. Since autobiographical memory is frequently altered in Alzheimer's disease (AD), we used this degenerative disorder as a model and applied a correlative approach between resting cerebral glucose utilization (CMRGlc) and temporally graded memory scores to identify the cerebral structures whose synaptic dysfunction subserves the impairment in autobiographical memory. To this end, we studied a group of 17 AD patients with mild to moderate dementia in whom autobiographical memory was assessed using a specially designed task from three broad time periods [the previous 5 years (period A); middle age (period B); and teenage and childhood (period C)], and measures of resting CMRGlc were obtained with PET. The patients performed less well than a control group for all three time periods and showed the expected temporal gradient, with the most remote period being best preserved (Ribot's gradient). Qualitative analysis showed that remote memories concerned generic (i.e. semantic) rather than specific (i.e. episodic) events. We found a significant positive correlation between autobiographical scores and the metabolism of the right hippocampus (extending to the lingual gyrus), restricted to period A. In addition, period A scores were significantly correlated with the right middle and inferior frontal gyri and the right middle temporal gyrus. Period B scores correlated chiefly with the prefrontal cortex bilaterally (bilateral superior, bilateral middle and right inferior gyri). Metabolic correlations with period C scores were restricted to the left middle frontal gyrus. These findings show striking differences in metabolic correlations with the autobiographical time period, in agreement with prevalent theories of normal functioning of human memory. Thus, in accordance with theories of long-term memory consolidation, we find the expected implication of the hippocampal region in the recall of recent memories, and a disengagement of this structure when the retention interval is beyond 5 years. Moreover, according to the hemispheric encoding/retrieval asymmetry model based on activation studies in healthy subjects, the fact that recent memories preferentially involved the right prefrontal cortex whereas remote memories involved the left prefrontal cortex supports the notion of semanticization of memories with time interval, such that preserved remote memories in AD have a predominantly semantic character.

Aged↗

PubMed2004

Semantic acquisition in childhood amnesic syndrome: a prospective study.

Amnesic patients can acquire new semantic knowledge despite a profound deficit of episodic memory. Although retrospective studies have been carried out on adults and children, prospective studies have been restricted to adults. The aim of the present work was to assess the acquisition of new semantic knowledge in amnesic children. The semantic protocol, composed of short, illustrated texts, was based on an original methodology which included an assessment of episodic memory on two occasions. Two amnesic children acquired new concepts despite major episodic disturbance, illustrated notably by a lack of recollection in episodic tasks. Our findings lend weight to the assumption that forming new semantic knowledge does not necessarily involve episodic memory, and provide methodological pointers for children's neuropsychological rehabilitation.

Amnesia↗

PubMed2004

Re-experiencing old memories via hippocampus: a PET study of autobiographical memory.

The time-scale of medial temporal lobe (MTL) involvement in storage and retrieval of episodic memory is keenly debated. To test competitive theories of long-term memory consolidation, the present work aimed at characterizing which cerebral regions are involved during retrieval of recent and remote strictly episodic autobiographical memory. Using positron emission tomography (PET), we examined mental retrieval of recent (0-1 year) and remote (5-10 years) autobiographical memories, controlling for the nature of the autobiographical memories (i.e., specificity, state of consciousness, vividness of mental visual imagery, emotion) retrieved during scanning by behavioral measures assessed at debriefing for each event recalled. Cognitive results showed that specificity and emotion did not change with time interval although both autonoetic consciousness and mental image quality were significantly higher for recent memories, suggesting an underlying shift in the phenomenal experience of remembering with the passage of time. The SPM analysis revealed common activations during the recollection of recent and remote memories that involved a widespread but mainly left-sided cerebral network, consistent with previous studies. Subtraction analysis demonstrated that the retrieval of recent (relative to remote) autobiographical memories principally activated the left dorsolateral prefrontal cortex whereas the retrieval of remote (relative to recent) autobiographical memories activated the inferior parietal cortex bilaterally. ROIs analysis revealed more hippocampal activity for remote memories than for recent ones and a preferentially right-sided involvement of the hippocampal responses whatever the remoteness of autobiographical memories. New insights based on higher hippocampal response to the remoteness of episodic autobiographical memories challenge the standard model and are less discrepant with the multiple trace theory.

Adult↗

PubMed2004

[Semantic memory in Alzheimer's disease: contributions of semantic priming].

Patients with Alzheimer's disease can be affected by semantic memory disorders from the onset of the dementia. Knowing precisely these disorders is important to improve the early diagnosis of Alzheimer's disease. Classical tests of semantic memory, such as naming and verbal fluency, highlight the existence of semantic disorders in the first stages of the disease. However, these tasks are not specific and involve cognitive processes (working memory, attentional resources), which are often disturbed in Alzheimer's disease. Therefore, they cannot attest the origin of the semantic disorders, which can be related either to a deficit of access to stored information in a preserved semantic network, or to the deterioration of the semantic memory network. Semantic priming paradigms, by minimizing the intervention of processes other than semantic, constitute relevant tools to study the integrity of the semantic network. However, the results of the studies devoted to the semantic priming effects in patients suffering from Alzheimer's disease are heterogeneous. This could be imputed, in part, to differences in experimental procedures. Nevertheless, some studies, conducted with a very controlled methodology, showed that semantic relationships used in the semantic paradigm as well as the semantic deficit severity have a serious impact on semantic priming effects. Taking into account these parameters, the results of semantic priming studies are more in accordance with the assumption of a storage degradation than with an access deficit. Moreover, these studies, and especially the observation of an hyperpriming effect, allow a better understanding of how semantic memory is degraded. The progressive deterioration begins at the level of the concept attributes, and further involves the concepts themselves.

Aged↗

PubMed2003

Working memory and executive functions in transient global amnesia.

Transient global amnesia (TGA) is usually considered to produce a profound impairment of long-term episodic memory, while at the same time sparing working memory. However, this neuropsychological dissociation has rarely been examined in detail. While a few studies have assessed some components of working memory in TGA, the results that have been obtained are far from conclusive. To clarify this issue, we carried out a comprehensive investigation of working memory in 10 patients during a TGA attack. In the first study, we report the results from three patients examined with a battery of neuropsychological tests designed to assess each of the three subcomponents of Baddeley's model of working memory. In a second study, seven different patients underwent neuropsychological investigations that focused specifically on the central executive system, using a protocol derived from a study by Miyake and colleagues. Our findings showed that subcomponents of working memory, such as the phonological loop and visuo-spatial sketch pad, were spared in TGA patients. Specific executive functions that entailed inhibitory control, dual task performance, updating and shifting mechanisms were also found to be normal. However, we found significantly impaired performance for the Brown-Peterson test, and that TGA patients were significantly impaired in the recollection of their episodic memories. They also made reduced numbers of 'remember' compared with 'know' judgments in the episodic memory test several days after TGA. On the basis of our findings, it would appear that the episodic memory deficit during TGA is not related to elementary aspects of executive functioning. Our data also highlight the nature of the cognitive mechanisms involved in the Brown-Peterson task, which may well depend on long-term memory (such as the process of semantic encoding). Lastly, the selective deficit in recollective episodic memories observed in TGA may be principally related to medial temporal lobe abnormalities that have been reported in this syndrome.

Aged↗

PubMed2003

Dissociating atrophy and hypometabolism impact on episodic memory in mild cognitive impairment.

The present study aims to unravel, in the same study, both morphological and functional specific substrates of encoding versus retrieval deficits in patients with amnestic mild cognitive impairment (MCI). For this purpose, 21 highly screened MCI patients with isolated memory impairment, who attended a memory clinic and fulfilled operational criteria for MCI, underwent (i) two episodic memory subtests designed to assess preferentially either incidental encoding or retrieval capacity; (ii) a high-resolution T1-weighted volume MRI scan; and (iii) a resting state [18F]fluoro-2-deoxy-D-glucose PET study. Using statistical parametric mapping, positive correlations between memory scores on one hand, and grey matter density and normalized partial volume effect-corrected brain glucose utilization (ncCMRglc) on the other hand, were computed. Deficits in both encoding and retrieval were correlated with declines in hippocampal region grey matter density. The encoding subtest also correlated with hippocampal ncCMRglc, whereas the retrieval subtest correlated with the posterior cingulate area ncCMRglc only. The present findings highlight a distinction in the neural substrates of encoding and retrieval deficits in MCI. Furthermore, they unravel a partial dissociation between metabolic and structural correlates, suggesting distinct interpretations. Hippocampal atrophy was related to both encoding and retrieval deficits, possibly reflecting a direct effect on hippocampal functioning, as well as an indirect effect, through remote functional disruption, on posterior cingulate region synaptic function, respectively.

Aged↗

PubMed2003

Autobiographical memory and autonoetic consciousness: triple dissociation in neurodegenerative diseases.

Few studies have investigated autobiographical amnesia in neurodegenerative diseases and yet these pathologies are particularly relevant when addressing the issue of theories of long-term memory consolidation. According to the standard model, the medial temporal lobe (MTL) is involved in the storage and retrieval of episodic and semantic memories during a limited period of years. An alternative model, the multiple trace theory (MTT), suggests that the capacity of the MTL to recollect episodic memories is of a more permanent nature. In order to test these models, we studied three groups of patients with a neurodegenerative disease predominantly affecting different cerebral structures namely the MTL (13 patients in the early stages of Alzheimer's disease) and the neocortex involving either the anterior temporal lobe (10 patients with semantic dementia) or the frontal lobe (15 patients with the frontal variant of frontotemporal dementia, fv-FTD). We compared these groups of patients with control subjects using an original and reliable autobiographical memory task designed specially to assess strictly episodic memory over the entire lifespan. This task, developed on the basis of the most up-to-date definition of episodic memory, takes into account the ability to mentally travel back in time and re-experience the source of acquisition (remembering, i.e. autonoetic consciousness) via the remember/know paradigm. All three groups of patients produced strongly contrasting profiles of autobiographical amnesia (regardless of the nature of the memories), which also differed markedly from that of the control group: temporally graded memory loss in Alzheimer's disease, showing that remote memories are better preserved than recent ones; memory loss with a reversed gradient in semantic dementia; and memory loss without any clear gradient in fv-FTD. Most strictly episodic memories (i.e. unique, specific in time and space, and detailed) were impaired, whatever the time interval considered in the three groups, though the memory loss was ungraded in Alzheimer's disease and fv-FTD, and temporally graded in semantic dementia, sparing the most recent period. A deficit of autonoetic consciousness emerged in Alzheimer's disease and fv-FTD, but not in semantic dementia, though beyond the most recent 12-month period, the latter group could not justify their subjective sense of remembering to the same extent as the controls, in terms of the actual contextual information retrieved-phenomenological, spatial or temporal details. Our results demonstrate that autobiographical amnesia varies according to the nature of the memories under consideration and the locus of cerebral dysfunction. They are discussed in the light of the two competing models of long-term memory consolidation and recent conceptions of autobiographical recollection: new insights based on current concepts of episodic memories challenge the standard model and tend to support the MTT instead.

Aged↗

PubMed2003

Semantic and episodic memory of music are subserved by distinct neural networks.

Numerous functional imaging studies have shown that retrieval from semantic and episodic memory is subserved by distinct neural networks. However, these results were essentially obtained with verbal and visuospatial material. The aim of this work was to determine the neural substrates underlying the semantic and episodic components of music using familiar and nonfamiliar melodic tunes. To study musical semantic memory, we designed a task in which the instruction was to judge whether or not the musical extract was felt as "familiar." To study musical episodic memory, we constructed two delayed recognition tasks, one containing only familiar and the other only nonfamiliar items. For each recognition task, half of the extracts (targets) were presented in the prior semantic task. The episodic and semantic tasks were to be contrasted by a comparison to two perceptive control tasks and to one another. Cerebral blood flow was assessed by means of the oxygen-15-labeled water injection method, using high-resolution PET. Distinct patterns of activations were found. First, regarding the episodic memory condition, bilateral activations of the middle and superior frontal gyri and precuneus (more prominent on the right side) were observed. Second, the semantic memory condition disclosed extensive activations in the medial and orbital frontal cortex bilaterally, the left angular gyrus, and predominantly the left anterior part of the middle temporal gyri. The findings from this study are discussed in light of the available neuropsychological data obtained in brain-damaged subjects and functional neuroimaging studies.

Adult↗

PubMed2003

The hyperpriming phenomenon in normal aging: a consequence of cognitive slowing?

Increased semantic priming effects (hyperpriming) are sometimes observed in Alzheimer's disease (AD) and in normal aging. Whereas the processes underlying this phenomenon are now well understood in AD, the interpretation is much more woolly in normal aging. To explore semantic priming, the authors used a lexical decision task in which the influence of attention and cognitive slowing was controlled. To explore the semantic organization, the words had coordinate (tiger-lion) or attribute relations (zebra-stripes). Priming scores of 21 older and 20 young participants were equivalent in the 2 conditions. These results reflect the integrity of semantic memory with normal aging and call into question some investigations showing hyperpriming for older participants; this may instead be an artifact of a general slowing effect.

Adult↗

PubMed2002

Mapping gray matter loss with voxel-based morphometry in mild cognitive impairment.

We used voxel-based morphometry to comprehensively and objectively map gray matter loss in 22 patients with amnestic mild cognitive impairment, defined as progressive isolated episodic memory decline. Compared with 22 age-matched healthy controls, patients had highly significant gray matter loss predominantly affecting the hippocampal region and cingulate gyri (posterior and subcallosal part of the anterior), and extending into the temporal neocortex. Compared with 16 age-matched patients with mild Alzheimer's disease, gray matter density was significantly preserved in mild cognitive impairment in the posterior association cortex. This pattern of gray matter loss in mild cognitive impairment agrees with but considerably expands upon previous region-of-interest based MRI studies, and is highly consistent with the course of neurofibrillary tangles across aging and Alzheimer's disease.

Aged↗

PubMed2002

The neural basis of intrusions in free recall and cued recall: a PET study in Alzheimer's disease.

This study was designed to map in Alzheimer's disease patients the correlations between resting-state brain glucose utilization measured by PET and the number of intrusions obtained by means of a specially designed episodic memory test separately in free recall and in cued recall. SPM revealed significant negative correlations between the number of intrusions in free recall and the metabolism of the right superior frontal gyrus. For the intrusions in cued recall, the negative correlations concerned the left rhinal cortex. Our findings suggest that intrusions in free recall reflect perturbations in strategic processes and that intrusions in cued recall are triggered by the cue in a relatively automatic manner. Frontal dysfunction would be responsible for the former and rhinal dysfunction for the latter.

Aged↗

PubMed2002

Episodic and semantic remote autobiographical memory in ageing.

Many laboratory studies have demonstrated an age effect on episodic memory which is in contrast with the preservation of semantic memory. The aim of this study was the assessment of age effects on autobiographical memory according to the length of the retention interval, taking into account the episodic and semantic components. A total of 52 subjects, aged between 40 and 79, were divided into four age groups. They were tested with a sophisticated autobiographical questionnaire consisting of two tasks, one involving the recall of semantic information and another the recall of episodic events. Results revealed that episodic recall deteriorated more with age and retention interval than semantic recall. These data, gathered using an ecological test, confirm age differences demonstrated by laboratory tests on the episodic-semantic distinction. Furthermore, the profile of results obtained for the recall of specific detailed events, and analysed according to age of encoding, confirms the distribution of episodic memories across the lifespan, as modelled by Rubin, Wetzler, and Nebes (1986) with the cue-word technique.

Adult↗

PubMed2002

The neural substrates of episodic memory impairment in Alzheimer's disease as revealed by FDG-PET: relationship to degree of deterioration.

In a previous investigation, we raised the hypothesis that in Alzheimer's disease the cerebral structures implicated in episodic memory deficits may differ according to the severity of cognitive impairment. To test this hypothesis, Story Recall test scores and PET measurements of resting cerebral glucose utilization, a measure of synaptic integrity, were obtained in 40 patients. Using SPM96 (statistical parametric mapping 1996), positive correlations between the two sets of data were calculated on a voxel basis, first in the whole patient sample and then separately in the two subgroups of 20 patients differing in Mini-Mental State Examination score, i.e. those with least impaired and those with most impaired performance ('less severe' and 'more severe' subgroups, respectively). In the whole sample, significant correlations (P < 0.05, corrected for multiple tests) involved bilaterally not only several limbic structures (the hippocampal/rhinal cortex regions, posterior cingulate gyrus and retrosplenial cortex) but also, and less expectedly, some temporo-occipital association areas. However, the subgroup analysis disclosed that, in the less severe subgroup, all significant correlations (P < 0.005, uncorrected) were restricted to the parahippocampal gyrus and retrosplenial cortex, in accordance with both the distribution of changes in tau in early Alzheimer's disease and the known involvement of this network in normal and impaired memory function, while in the more severe subgroup they mainly involved the left temporal neocortex, which is known to be implicated in semantic memory. These findings suggest that, when episodic memory is mildly impaired, limbic functions are still sufficient to subserve the remaining performance, whereas with more severe memory deficit resulting from accumulated pathology the neocortical areas that are normally involved in semantic memory are recruited, perhaps as a form of (inadequate) compensatory mechanism.

Aged↗

PubMed2002

The dynamic time course of semantic memory impairment in Alzheimer's disease: clues from hyperpriming and hypopriming effects.

The nature of semantic memory deficit in Alzheimer's disease is still a matter of controversy. To clarify this issue, we examined the evolution of semantic memory impairment in 24 Alzheimer's disease patients by means of a longitudinal study. We used two semantic tasks, one explicit and the other implicit, to evaluate the integrity of the same concepts. The explicit task was a semantic knowledge task composed of naming and questions, involving superordinate and attribute knowledge of concepts. The implicit task, a lexical decision task, assessed semantic priming and allowed a very pure measurement of semantic memory. In this task, related pairs of words had coordinate (e.g. "tiger-lion") or attribute ("tiger-stripe") relationships. In the coordinate relation between two words, the semantic priming performances were at first paradoxical: they increased abnormally (hyperpriming) before falling down, whereas in the attribute condition, the priming effects were first normal and then started to decrease in the final sessions (hypopriming). Compared with the semantic knowledge performance, these apparently disconcerting results reflect a coherent pattern of semantic memory degradation in Alzheimer's disease that is a progressive deterioration starting with specific attribute information. The data reveal in an astonishing yet striking manner the dynamic semantic memory degradation in Alzheimer's disease through the apparently paradoxical semantic priming effects.

Aged↗

PubMedDate not supplied

Executive functioning and judgment-of-learning versus feeling-of-knowing in older adults.

Feeling-of-knowing (FOK) accuracy and judgment-of-learning (JOL) accuracy were compared on separate, identical, episodic-memory tasks. The results indicated that these two measures were not correlated, suggesting that they do not tap the same metacognitive ability. We also looked at whether FOK and JOL accuracies were related differently to higher order executive functioning. In order to take advantage of within-subject variability in cognitive performance, older adults were selected as participants. They were administered the standard neuropsychological tests used to assess executive functioning. A correlational analysis clearly showed that only FOK accuracy was correlated with the executive measures, suggesting that executive control is not equally implicated in FOK and JOL.

Aged↗